Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Biopolyimides poly(ATA-CBDA) made from of 4,4'-diamino-alpha-truxillic acid dimethyl ester (ATA) and 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) were synthesized and its electric volume resistivity measured at various electric voltages at 10-60 degrees C. The volume resistivity for Kapton and biopolyimide films showed a sudden decrease at a critical electric field of 2.6 x 10(7) and 1.0 x 10(7) V/m, respectively. The activation energy at low electric field for Kapton and biopolyimide was 68 and 90 kJ/mol, respectively, meanwhile at high electric field for Kapton and biopolyimide was 45 and 74 kJ/mol, respectively. These results indicate that the carriers for electric conduction for biopolyimide weakly interact with the polymer chain and the biopolyimide contains many conductive carriers than Kapton.

DOI： 10.1246/cl.200232

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier B.V.  

It is of great significance to use cheaper macro-porous supports for NaA membranes. Herein, a chitosan modified strategy was designed to weaken the accurate matching between defective supports and seeds. Two types of defective α-alumina tubes were used as macro-porous supports. In order to further reduce the fabricating cost, non-uniform NaA seeds (0.3–3.2 μm) were prepared without the expensive structure-directing agent. By one simple dip coating process, the chitosan layer was coated on the surface of defective supports before applying seeds. Moreover, the binding strength of adsorbed crystals was qualitatively investigated by the ultrasonic treatment (35 kHz, 5 min). NaA membranes were subsequently prepared by the secondary crystallization process. The results indicated that the addition of a thin chitosan buffer layer really overcame the limitation of obvious defects (&gt
10 μm). Meanwhile, as for the obvious cracks of 1.5% chitosan modified NaA membranes, the unbalanced hydrophilic swelling was offered as a feasible explanation. The optimized separation factor was 4000 with the flux of 1.32 kg m−2 h−1 (70 °C, 0.03 Pa). Overall, this efficient method can be treated as one potential strategy to prepare low-cost NaA membranes.

DOI： 10.1016/j.micromeso.2019.109648

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

The effect of a magnetic field on the water contact angle for magnetic elastomers with various plasticizer contents was investigated. At a plasticizer content below 60 wt %, there was no change in contact angle when a magnetic field of 370 mT was applied. For magnetic elastomers with a plasticizer content above 65 wt %, a change in contact angle of approximately 8.0 degrees was observed (e.g. 38 degrees at 0 mT and 46 degrees at 370 mT for 65 wt % plasticizer content). Dynamic viscoelastic measurements showed that magnetic elastomers with a plasticizer content below 60 wt % demonstrate the magnetorheological (MR) effect with changes in storage modulus higher than similar to 1 MPa. Atomic force microscopy for magnetic elastomer with a plasticizer content of 50 wt % revealed that the averaged Young's modulus was 233 +/- 52.1 kPa at 370 mT and 83 +/- 5.4 kPa at 0 mT, indicating that the MR effect is caused not only on a bulk but also on a mesoscopic scale. Magnetic elastomers specialized for cell culture were obtained by optimizing the plasticizer content, that exhibit the MR effect with changes in storage modulus from 1.3 x 10(4) Pa to 9.4 x 10(5) without changing the surface properties.

DOI： 10.1246/cl.190929

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

The magnetic response of the storage modulus for bimodal magnetic elastomers containing magnetic particles with a diameter of 7.0 μm and plastic beads with a diameter of 200 m were investigated by varying the volume fraction of plastic beads up to 0.60 while keeping the volume fraction of the magnetic particles at 0.10. The storage modulus at 0 mT for monomodal magnetic elastomers was 1.4 x 104 Pa, and it slightly increased with the volume fraction of plastic beads up to 0.6. The storage modulus at 500 mT for bimodal magnetic elastomers at volume fractions below 0.25 was constant, which was equal to that for the monomodal one (=7.9 x 104 Pa). At volume fractions of 0.25-0.40, the storage modulus significantly increased with the volume fraction, showing a percolation behavior. At volume fractions of 0.40-0.60, the storage modulus was constant at 2.0 x 105 Pa, independently of the volume fraction. These results indicate that the enhanced increase in the storage modulus was caused by the chain formation of the magnetic particles in vacancies made of plastic beads.

DOI： 10.3390/polym12020290

Scopus

researchmap

Publishing type：Research paper (scientific journal)   Publisher：{MDPI} {AG}  

DOI： 10.3390/biom10010155

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI Multidisciplinary Digital Publishing Institute  

A magnetic-responsive elastomer consisting of magnetic elastomer and zinc oxide with a tetrapod shape and long arms was fabricated mimetic to the tissue of sea cucumber in which collagen fibrils are dispersed. Only the part of magnetic elastomer is active to magnetic fields, zinc oxide plays a role of reinforcement for the chain structure of magnetic particles formed under magnetic fields. The magnetic response of storage modulus for bimodal magnetic elastomers was measured when the magnetic particle was substituted to a nonmagnetic one, while keeping the total volume fraction of both particles. The change in storage modulus obeyed basically a mixing rule. However, a remarkable enhancement was observed at around the substitution ratio of 0.20. In addition, the bimodal magnetic elastomers with tetrapods exhibited apparent change in storage modulus even at regions with a high substitution ratio where monomodal magnetic elastomers consist of only magnetic particles with less response to the magnetic field. This strongly indicates that discontinuous chains of small amounts of magnetic particles were bridged by the nonmagnetic tetrapods. On the contrary, the change in storage modulus for bimodal magnetic elastomers with zinc oxide with irregular shape showed a mixing rule with a substitution ratio below 0.30. However, it decreased significantly at the substitution ratio above it. The structures of bimodal magnetic elastomers with tetrapods and the tissue of sea cucumber with collagen fibrils are discussed.

DOI： 10.3390/biomimetics4040068

Scopus

researchmap

Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Biopolyimides poly(ATA-CBDA), made from of 4,4′-diamino-α-truxillic acid dimethyl ester (ATA) and 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), is synthesized and measured its electric volume resistivity at various experimental conditions. The effects of film size, thickness, drying time, and the electric field strength on electric resistivity are investigated and compared with polyimide (Kapton). The electric resistivity for all polyimide and biopolyimide are distributed in the range of 1015–1016 Ωcm, which shows that biopolyimide has high electrical insulation as well as polyimide. The electric resistivity strongly depends on film thickness, which suggests that electric resistivity is a function of electric field strength. The critical electric field for polyimide and biopolyimide films are determined to be 5.8 × 107 V/m and 3.2 × 107 V/m, respectively. Humidity was found to strongly affect the electric resistivity; ~1016 Ωcm at 34% RH and ~1013 Ωcm at 60% RH for both polyimide and biopolyimide films.

DOI： 10.3390/polym11101552

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI Multidisciplinary Digital Publishing Institute  

The relation between the number of magnetic particles and the change in storage modulus induced by a magnetic field was investigated for weak hydrogels containing carbonyl iron, iron oxide, and barium ferrite particles with different diameters in primary particles while maintaining the magnetization of magnetic particles. The change in storage modulus exhibited a power dependency against the number of magnetic particles, which was nearly independent of the magnetic particles. The change in storage modulus was successfully scaled by the reduced number of magnetic particles using the diameter of secondary particles. Microphotographs revealed that iron oxide and barium ferrite particles form aggregations while carbonyl iron particles are well dispersed in carrageenan gels. The diameter of secondary particles determined by a relation between the change in storage modulus and the reduced number of magnetic particles showed similar values with those observed in microphotographs.

DOI： 10.3390/gels5030039

Scopus

researchmap

Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.dib.2019.104114

researchmap

DOI： 10.1016/j.jcis.2019.03.062

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

The morphology of magnetic particles with a size of 7.0 _m was observed for magnetic elastomers with a concentration of magnetic particles of 70 wt% using an X-ray microscope remolded into high resolution. Computed tomography images revealed that magnetic particles were distributed isotopically in the absence of a magnetic field, but they formed a chain structure in the polyurethane network under a magnetic field of 270 mT. It was also established, by image analysis, that magnetic elastomers had an anisotropic structure under the magnetic field.

DOI： 10.3390/ijms20122879

Scopus

PubMed

researchmap

DOI： 10.1016/j.polymdegradstab.2019.01.036

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

Magnetorheological elastomers (MREs) are stimulus-responsive soft materials that consist of polymeric matrices and magnetic particles. In this study, large-strain response of MREs with 5 vol % of carbonyl iron (CI) particles is experimentally characterized for two different conditions: (1) shear deformation in a uniform magnetic field; and (2), compression in a heterogeneous uniaxial magnetic field. For condition (1), dynamic viscoelastic measurements were performed using a rheometer with a rotor disc and an electric magnet that generated a uniform magnetic field on disc-like material samples. For condition (2), on the other hand, three permanent magnets with different surface flux densities were used to generate a heterogeneous uniaxial magnetic field under cylindrical material samples. The experimental results were mathematically modeled, and the relationship between them was investigated. We also used finite-element method (FEM) software to estimate the uniaxial distributions of the magnetic field in the analyzed MREs for condition (2), and developed mathematical models to describe these phenomena. By using these practicable techniques, we established a simple macroscale model of the elastic properties of MREs under simple compression. We estimated the elastic properties of MREs in the small-strain regime (neo⁻Hookean model) and in the large-strain regime (Mooney⁻Rivlin model). The small-strain model explains the experimental results for strains under 5%. On the other hand, the large-strain model explains the experimental results for strains above 10%.

DOI： 10.3390/ijms19103045

Web of Science

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier B.V.  

We measured the sound velocity for magnetic soft composites consisting of a polymeric matrix of polyurethane and a magnetic particle of carbonyl iron or barium ferrite, and investigated the effect of the particle dispersibility on the sound velocity at 10 MHz for the composites. Morphological observations and dynamic viscoelastic measurements at 1 Hz were also carried out, and the results revealed that the carbonyl iron was dispersive particle and the barium ferrite was aggregative particle in the polyurethane matrix. The sound velocity for polyurethane elastomer without magnetic particles was 1444 ± 12 m/s and it decreased with the volume fraction of magnetic particles. The sound velocity of magnetic composites with barium ferrite obeyed the Reuss model at whole volume fractions, however, magnetic composites with carbonyl iron exhibited an under deviation from the Reuss model at volume fractions above ~0.053. It was also found that the longitudinal modulus was insensitive to the creation of the particle network and sensitive to the aggregation of magnetic particles. The threshold seen in the longitudinal modulus was different from that in the nonlinear parameter of viscoelasticity, indicating that the ultrasound of 10 MHz detects microscopic heterogeneity of particle dispersion.

DOI： 10.1016/j.reactfunctpolym.2018.05.011

Web of Science

Scopus

researchmap

DOI： 10.1246/cl.180511

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

The effect of a weak magnetic field on vibration transmissibility was investigated for magnetic elastomers with various volume fractions of magnetic particles. Polyurethane elastomers without magnetic particles exhibited a natural frequency at 53 Hz and were insensitive to a magnetic field of 60 mT. The natural frequency for magnetic elastomers with a volume fraction of 0.23 was 115 Hz at 0 mT, and increased to 134 Hz at 60 mT. The vibration transmissibility was independent of the magnetic field. A linear relation between the natural frequency and (G/m)1/2 was observed (G: storage modulus, m: mass), indicating that the observed vibration is basically described by a simple harmonic oscillation.

DOI： 10.3390/polym10010104

Web of Science

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

Polymers, derived from bio-derived resources, have gained considerable momentum because of a lower dependence over conventional fossil-based resources without compromising the materials' thermo-mechanical properties. Unique characteristics of organic and inorganic materials can be incorporated by a combination of both to obtain hybrid materials. We have recently developed a series of transparent biopolyimides (BPI) from a biologically derived exotic amino acid, 4-aminocinnamic acid (4ACA) to yield 4-amino truxillic ester (4ATA ester) derivatives. In the present research, the polyimide-precursor was subjected to sol-gel polycondensation reactions with silicon-alkoxide followed by annealing under vacuo to yield a biopolyimide-silica hybrid. The biopolyimide structures (4ATA acid/ester) and their silica hybrids thermo-mechanical, electrical and optical performance were evaluated. It was found that the biopolyimide with 4ATA(ester) yields thermo-mechanically robust films with very high electrical stability as well as optical transparency, plausibly due to the uniform dispersion of the silica particles in the biopolyimide matrix.

DOI： 10.1039/c8ra01965g

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIMS Press  

The effect of plasticizer content on the vibration absorbing properties for polyurethane elastomers was investigated. A natural frequency appeared on the frequency spectra at around 100 Hz. The natural frequency linearly decreased, and the transmissibility also decreased with the plasticizer content. Magnetic elastomers containing carbonyl iron particles with a dimeter of 7.0 μm also showed a natural frequency at ~260 Hz, and the natural frequency significantly decreased with the plasticizer content. The decrease in the transmissibility with the plasticizer content was larger than that for polyurethane elastomers. The natural frequency for magnetic elastomers increased by several ten Hz by a magnetic field of 60 mT although the transmissibility was independently of the plasticizer content. The effect of load on the natural frequency for these elastomers was also investigated, and it was found that the natural frequency is proportional to the storage modulus, G, with different two slopes depending on the mass of the system, m. The linear relation between the natural frequency and (G'/m)1/2 revealed that the observed vibration can be basically described by a simple harmonic oscillation.

DOI： 10.3934/matersci.2018.1.44

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

A device consisting of a phase of magnetic elastomer, a phase of polyurethane foam (PUF), and permanent magnet was fabricated and the stress-strain curves for the two-phase magnetic elastomer were measured by a uniaxial compression measurement. A disk of magnetic elastomer was adhered on a disk of PUF by an adhesive agent. The PUF thickness was varied from 1 mm to 5 mm while the thickness of magnetic elastomers was constant at 5 mm. The stress at a strain of 0.15 for the two-phase magnetic elastomers was evaluated in the absence and in the presence of a magnetic field of 410 mT. The stress at 0 mT decreased remarkably with the PUF thickness due to the deformation of the PUF phase. On the other hand, the stress at 410 mT slightly decreased with the thickness; however, it kept high values even at high thickness. When the PUF thickness was 5 mm, the maximum stress increment with 45 times to the off-field stress was observed. An experiment using ping-pong balls demonstrated that the coefficient of restitution for the two-phase magnetic elastomers can be dramatically altered by the magnetic field.

DOI： 10.1088/2053-1591/aa9d51

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

The relationship between magnetic-field sensitivity and the volume fraction of magnetic particles for magnetic elastomers was investigated. The magnetic-field dependence of the storage modulus for magnetic elastomers was measured by dynamic viscoelastic measurements under magnetic fields with a constant sweep rate of 3.7 mT s(-1). The magnetic-field sensitivity was determined by the initial slope of the storage modulus using an exponential function. It was revealed that the maximum magnetic-field sensitivity was 1.8 x 10(-2) mT(-1) at the maximum volume fraction of magnetic particles.

DOI： 10.1246/cl.170735

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We studied the size effect of disk-shaped magnetic elastomers, which were placed on a permanent magnet, on their magnetomechanical response for the permanent magnet. The diameter of the magnetic elastomers varied from 14 to 40 mm, whereas the diameter of the permanent magnet was constant at 30 or 35 nun. The smallest magnetic elastomer did not exhibit magnetomechanical response for both 30- and 35-mm-diameter permanent magnets; however, a clear response was observed when the diameter of the magnetic elastomer equaled that of the permanent magnet. Magnetic field distribution revealed a steep gradient of magnetic fields at the fringe of permanent magnets. Image analyses indicated that the bottom of magnetic elastomers was restricted to deform along the horizontal direction under compression. In the vertical direction, the magnetostriction due to the magnetic attractive force from permanent magnets was negligibly small. Therefore, the size-dependent behavior of magnetomechanical response is considered a pinning effect wherein the bottom of magnetic elastomers was restricted by the magnetic field gradient in the horizontal direction. We also analyzed the magnetomechanical response of magnetic elastomers when magnetic fields were applied by square-or ring-shaped permanent magnets.

DOI： 10.1016/j.reactfunctpolym.2017.05.009

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

We studied the effects of magnetic field strength and sample size on the magnetomechanical response for disk-shaped magnetic elastomers placed on a permanent magnet. The diameter of magnetic elastomer was varied between 14-40 mm, whereas the height was constant at 5 mm. The stress was measured with a unidirectional compression apparatus. It was found that the smallest magnetic elastomer with 14mm diameter did not exhibit magnetomechanical response, on the other hand, clear response was observed for magnetic elastomers with 35mm diameter. This sample size effect was observed at both 310 and 420mT.

DOI： 10.1246/cl.161182

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Sound velocity of magnetic elastomers containing carbonyl iron and barium ferrite particles has been investigated by using an ultrasound pulse-echo method at 10 MHz. The sound velocity for magnetic elastomers containing barium ferrite was independent of the sample thickness, and the mean sound velocity was determined to be 1187 +/- 5 ms(-1). The sound velocity for magnetic elastomers containing carbonyl iron linearly decreased with the sample thickness, and the values (954-1031 ms(-1)) were lower than those of barium ferrite. Microphotographs revealed that carbonyl iron particles were randomly dispersed and barium ferrite particles were heterogeneously dispersed in the polyurethane matrix. The relationship between the sound velocity and the particle dispersibility is discussed.

DOI： 10.1246/cl.161080

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

We have investigated the transition from linear viscoelasticity to nonlinear viscoelasticity for bimodal magnetic elastomers under a magnetic field. For bimodal magnetic elastomers, the transition strain increased remarkably with the volume fraction of nonmagnetic particles. For monomodal magnetic elastomers, the transition strain also increased with the volume fraction of magnetic particles; however, the increment was not significant. A possible mechanism of the widening of the linear viscoelastic plateau by nonmagnetic particles is discussed.

DOI： 10.1246/cl.161079

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The electric-voltage dependence of the electric conductivity for cross-linked and un-cross-linked magnetic elastomers was measured at various magnetic fields, and the effect of cross-linking on the electric conductivity and the dielectric-breakdown behavior was investigated. The electric conductivity for uncross-linked elastomers at low voltages was independent of magnetic fields and the volume fraction of magnetic particles, indicating the electric conduction in the polyurethane matrix. At high voltages, the electric conductivity increased with the magnetic field, showing the electric conduction via chains of magnetic particles. On the other hand, the electric conductivity at low voltages for cross-linked elastomers with volume fractions below 0.06 was independent of the magnetic field, suggesting the electric conduction in the polyurethane matrix. At volume fractions above 0.14, the electric conductivity increased with the magnetic field, suggesting the electric conduction via chains of magnetic particles. At high voltages, the electric conductivity for cross-linked elastomers with a volume fraction of 0.02 was independent of the magnetic field, indicating the electric conduction through the polyurethane matrix. At volume fractions above 0.06, the electric conductivity suddenly increased at a critical voltage, exhibiting the dielectric breakdown at the bound layer of magnetic particles and/or the discontinuous part between chains.

DOI： 10.1021/acs.jpcb.6b12875

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：HINDAWI PUBLISHING CORP  

The size effect of magnetomechanical response of chemically cross-linked disk shaped magnetic elastomers placed on a permanent magnet has been investigated by unidirectional compression tests. A cylindrical permanent magnet with a size of 35 mm in diameter and 15 mm in height was used to create the magnetic field. The magnetic field strength was approximately 420 mT at the center of the upper surface of the magnet. The diameter of the magnetoelastic polymer disks was varied from 14 mm to 35 mm, whereas the height was kept constant (5 mm) in the undeformed state. We have studied the influence of the disk diameter on the stress-strain behavior of the magnetoelastic in the presence and in the lack of magnetic field. It was found that the smallest magnetic elastomer with 14 mm diameter did not exhibit measurable magnetomechanical response due to magnetic field. On the opposite, the magnetic elastomers with diameters larger than 30 mm contracted in the direction parallel to the mechanical stress and largely elongated in the perpendicular direction. An explanation is put forward to interpret this size-dependent behavior by taking into account the nonuniform field distribution of magnetic field produced by the permanent magnet.

DOI： 10.1155/2017/8605413

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The magnetic-field dependence of the storage modulus for bimodal magnetic elastomers consisting of carbonyl iron with a diameter of 2.8 mu m (magnetic) and aluminum hydroxide with a diameter of 1.4 mu m (nonmagnetic) was measured, and the effect of nonmagnetic particles on the magnetic-field sensitivity of the storage modulus was investigated. The coefficient of the magnetic-field sensitivity for the monomodal magnetic elastomer increased from 0.018 to 0.026 mT(-1) for the bimodal one by embedding nonmagnetic particles of 6.6 vol %. At volume fractions above 5.4 vol %, the bimodal magnetic elastomer exhibited significant nonlinear viscoelasticity at 0 mT and a high storage modulus, at 500 mT, simultaneously, the coefficient of the magnetic-field sensitivity demonstrated high values. This strongly indicates that both the particles form a particle network at the off-field, and they make a well-developed chain structure under magnetic fields. The time profiles of the storage modulus for bimodal magnetic elastomers can be fitted by a linear combination of two exponential functions with two characteristic times showing the alignment of magnetic particles. The alignment time for the fast and slow processes was distributed around 3.3 +/- 0.3 and 176 +/- 12 s, respectively. The alignment time was independent of the volume fraction of the nonmagnetic particles; however, the increment in the storage modulus for the fast process significantly increased at volume fractions above 5.4 vol %. It was also revealed that the coefficient of the magnetic-field sensitivity can be scaled by a power function of the inclement in the storage modulus divided by the off-field modulus, Delta G'/G(0)', not only for the bimodal magnetic elastomers but also for the monomodal ones.

DOI： 10.1021/acs.jpcb.6b08622

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

We have investigated the mechanical loss factor for bimodal magnetic elastomers containing magnetic and nonmagnetic particles. The bimodal magnetic elastomer exhibited amphoteric response of loss factor by magnetic fields depending on the strain amplitude; i.e. negative response at low strains and significant positive response at high strains. The mechanism of amphoteric response seen in bimodal magnetic elastomers is discussed.

DOI： 10.1246/cl.160327

Web of Science

researchmap

Publishing type：Research paper (scientific journal)  

A study was conducted to fabricate a microstructure on a poly(dimethylsiloxane) (PDMS) surface using a porous silicon wafer as a mold. The microstructured PDMS surfaces were deposited with gold and imaged using scanning electron microscopy (SEM). The average height and width of the microrods measured using scanning electron microscopy imaging were 10 and 8 μm. The results show that the water contact angle was 103° on the flat surface and 131° on the microstructured surface, resulting in the microstructure increased hydrophobicity.

DOI： 10.1038/pj.2016.34

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

The effect of plasticizer content on the magnetic-field sensitivity for magnetic elastomers has been investigated while maintaining the concentration of magnetic particles at 70 wt %. The magnetic-field dependence of the storage modulus for magnetic elastomers was measured by dynamic viscoelastic measurements under magnetic fields with a sweep rate of 3.7 mTs(-1). The magnetic-field sensitivity, determined by the initial slope of the storage modulus using an exponential function, increased from 1.0 x 10(-3) to 1.8 x 10(-2) mT(-1) with increasing plasticizer content.

DOI： 10.1246/cl.160363

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Adhering hydrogel systems are important particularly in the medical field because they can be used as adhesives cross linking between living tissues. In this research, hydrogels including cationic substituents prepared via free-radical polymerization were brought into contact after applying an aqueous dispersion of the layered inorganic compound Micromica to their surfaces. As a result, the hydrogels adhered to each other due to the intercalation of cationic substituents included in the gel networks into the interlayers of Micromica. As the water content ratio of hydrogels decreased, the adhesive strength came to be higher, and finally the adhesively bonded joint supported a tensile load of 10 kg. Moreover, it was confirmed that the adhered hydrogels have high tolerance toward various environments, such as high or low temperatures and solvents.

DOI： 10.1021/acsmacrolett.6b00337

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

In this work, cationic and anionic microgels which are mainly formed from thermal responsive polymer, poly(N-isopropylacrylamide), are prepared and mixed in water. These microgels interact with each other due to the electrostatic interaction, and aggregate voluntarily. By applying the microgel aggregating system, photo-responsive aggregating system is constructed by using o-nitrobenzaldehyde (NBA), which reacts and releases hydrogen triggered by photo stimuli. The microgel aggregates in an aqueous solution of NBA re-disperse depending on the irradiation time of UV light. In addition, by masking the UV irradiated area, the resultant shapes of microgel aggregates are controlled. The aggregated microgel shows rapid and drastic volume changes in response to heat. (C) 2015 Wiley Periodicals, Inc.

DOI： 10.1002/pola.27985

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Physically crosslinked sacran gels were prepared, and the degree of swelling in pure water and in 0.9 wt % NaCl solution was measured. The sacran gel showed anomalous swelling with a degree of swelling of 6100 in pure water and 530 in the saline solution. The degree of swelling varied remarkably by the pH of the pre-gel solution. This high swelling ratio might originate from the large mesh consisting of extremely long chains of sacran.

DOI： 10.1246/cl.151125

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

C-60 fullerene derivatives, which are formed by grafting polymer chains on a C-60 fullerene, can improve the solubility of C-60 in solvents. These derivatives are able to composite with various functional polymers to form interpenetrating network gel structures. In this study, a composite gel composed of the C-60 fullerene derivatives and poly(3,4-ethylenedioxythiophene)(PEDOT) was prepared using a low-temperature organic-solvent process, and its photoelectric properties were evaluated. Furthermore, the poly(ethylene glycol) (PEG) radicals were successfully trapped in the fullerene (C-60), which worked as a cross-linking point to yield the C-60-PEG gel. Then, PEDOT was composited with the gel using chemical oxidative polymerization to form the C-60-PEG/PEDOT gel. The structure of the film prepared using this composite material was identified. The C-60-PEG/PEDOT film had an amorphous network structure and the UV response was much higher than that of the C-60-PEG gel. In addition, it was estimated that PEDOT was synthesized inside the C-60-PEG gel and formed nanoscale junctions between C-60 and PEDOT, which was beneficial for the movement of electrons and holes. The photocurrent was observed by irradiating the C-60-PEG/PEDOT gel electrode with UV or simulated sunlight. The power conversion efficiency (PCE) was calculated as 1.2 x 10(-3)%. Therefore, it is expected that the C-60-PEG/PEDOT material is applicable for the photoelectric field, such as solar cells.

DOI： 10.1038/pj.2015.65

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

In order to create more flexible and robust soft actuators, organic/inorganic hybrid actuating fibers were prepared by coating gold fibers in polypyrrole using electropolymerization. The linear, coiled, and helical hybrid fibers were prepared by deforming gold fibers in advance. The obtained fibers exhibit various actuating motions, such as bending, stretching, and rotating motions, due to shrinking and expanding of polypyrrole by doping and de-doping of lithium cations. Merit of the actuating fibers prepared in this research is that the fibers are thin and can be easily combined. Hence, the actuating forces of the fibers caused by doping and de-doping can be amplified by combining the fibers. As a result, heavier weights could be lifted, proportional to the number of fibers combined.

DOI： 10.1246/cl.150851

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

DOI： 10.1038/pj.2015.47

Web of Science

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)  

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Porous poly(pyrrole) (PPy) films are prepared by utilizing agar particles (APs) of various average diameters as templates. The size of the APs can be regulated by the concentration of agar during preparation, and these APs can be removed easily from PPy films by heating up to 90 degrees C after formation of the films by electropolymerization because agar shows a thermally reversible sol-gel transition. The pores in the surface of PPy films can be controlled by the size of APs utilized as templates. The porous PPy films have higher mechanical strength and exhibit the more dynamic actuating behavior than the flat PPy films. Moreover, spring-like actuating motion is induced by the presence of pores in the surface of helically shaped PPy films.

DOI： 10.1002/mame.201500047

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The elastic modulus for bimodal magnetic elastomers has been investigated by compression measurements under large deformation. The bimodal magnetic elastomers consist of carbonyl iron magnetic particles and zinc oxide nonmagnetic particles. The Young's modulus for monomodal magnetic elastomers was 8.94 x 10(4) Pa at 0 mT and 1.65 x 10(5) Pa at 320 mT, respectively. The relative change in the Young's modulus for monomodal magnetic elastomer was 1.8, and it was raised to 5.8 only by mixing with the nonmagnetic particles of 9.6 vol. %. It is considered that the modulus enhancement originates from the stress transfer by the additional chains of magnetic particles via nonmagnetic particles. The electric resistivity analysis revealed that 27% of magnetic particles in a strand of chains were replaced by nonmagnetic particles. It was shown in the present study that the bimodal magnetic elastomers endured against a compression load of 30 N. (c) 2015 AIP Publishing LLC.

DOI： 10.1063/1.4926646

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Magnetic polyurethane elastomers containing various plasticizers were synthesized, and the effect of plasticizers on the magnetoelastic behavior has been investigated. The storage modulus for magnetic elastomers at 0 mT decreased with plasticizer content, whereas the storage modulus at 500 mT dramatically increased. The increment in the storage modulus by magnetic fields increased with plasticizer content indicating a well-developed chain structure of magnetic particles. It was found that the on-field storage modulus can be scaled by the off-field modulus independently of the kind of plasticizers.

DOI： 10.1246/cl.140932

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

Sacran is a supergiant cyanobacterial polysaccharide with an extremely high absolute molecular weight that exceeds 107 g mol-1 (molecular length: over 30 μm). Sacran forms milli-scaled orientation domains in aqueous liquid crystalline (LC) state, even in trace concentrations i.e. 0.3 wt%. Aqueous sacran films that are cast from a LC state and annealed between 70-140 °C form self-standing sheets composed of oriented hydrogels. When sacran films swell, they experience changes in size that are 70 fold higher in relation to thickness than those that occur in relation to width. Either an increase in film thickness or a decrease in sacran chain length reduces swelling anisotropy, demonstrating that stress that occurs during drying can be effectively used to propagate the cooperative alignment of LC chains on a micrometer sized scale comparable with the thickness of self-standing films.

DOI： 10.1039/c5ra18585h

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

We synthesized layered magnetic elastomers with polymer films and investigated the magnetoelastic behavior using dynamic viscoelastic measurements. The storage modulus at 0 mT was nearly independent of the sheets of films, while the storage modulus at 500 mT dramatically increased. The storage modulus at 500 mT for magnetic elastomers with 4 films was 2.1 MPa, which was 1.3 MPa higher than that of magnetic elastomers without layered structure. It can be considered that the stress transfer among imperfect short chains of magnetic particles is enhanced by inserting polymer films.

DOI： 10.1246/cl.140723

Web of Science

researchmap

Language：English   Publishing type：Part of collection (book)   Publisher：Springer Japan  

Magnetic soft materials containing solid state magnetic particles demonstrate various motions and magnetorheological behavior in response to magnetic fields. When a rotational magnetic field is applied to magnetic gels containing with magnetized particles, the magnetic gels exhibit rotational motion. When a non-uniform magnetic field is applied to magnetic gels, the elongation of magnetic gels is observed. The rotational motion of magnetic gels can be applied to a fluid pump that delivers water in straight and spiral tubes. A bead of magnetic gels loaded with drugs undergoes accelerated drug release depending on the rotation rates. The elongational motion of magnetic gels can be applied to an elongation-contraction actuator or a microvalve. Under uniform magnetic fields, the magnetic gels show variable viscoelastic behavior depending on the field-strength, which is called the magnetorheological effect. The dynamic modulus of magnetic hydrogels increases by two orders of magnitude synchronized with magnetic fields. The magnetorheological effect of magnetic gels can be applied to haptic devices or intelligent dampers. Actuators and magnetorheological effects of magnetic soft materials consisting of solid state magnetic particles are described.

DOI： 10.1007/978-4-431-54767-9_20

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Additions of single-walled carbon nanotubes (SWCNTs) to kappa-carrageenan gels weaken thixotropy. The minimum volume fraction of SWCNT to kappa-carrageenan necessary to affect thixotropy is about 10(-4). Confocal Raman microscopy reveals that SWCNTs are preferentially located close to the hole perimeter native to the gel network. This suggests that the destruction of network initiates at the hole perimeter. By locating at the critical region, only a small amount of SWCNTs is sufficient to resist initiating destruction.

DOI： 10.1246/cl.140205

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

We have investigated the electric conductivity, dielectric relaxation behavior, and viscosity for the aqueous solution of cyanobacterial megamolecules, molecular weight =1.6×107 g/mol, named sacran. Sacran is an anionic polyelectrolyte which has carboxylate and sulfate groups on the saccharide chain. The electric conductivity and the zero shear viscosity demonstrated three crossover concentrations at 0.004, 0.02, and 0.1 wt%. The viscosity was found to be scaled as ∼c1.5, ∼c0.5, ∼c1.5, and ∼c3.0 with increasing the sacran concentration. At 0.1 wt%, the sacran chain formed a weak gel which exhibits macroscopic liquid crystal domains including Schlieren texture. Therefore, these crossover concentrations are considered to be the overlap concentration, entanglement concentration, and gelation concentration (or critical polyelectrolyte concentration), respectively. Dielectric relaxation analysis exhibited the fact that sacran has two types of counterions with different counterion-polyion interaction, i.e., strongly bound and loosely bound counterions. The dielectric parameters such as relaxation time or relaxation strength are sensitive to both the entanglement concentration and the gelation concentration, but not the overlap concentration. The number density of bound counterions calculated from the relaxation strength revealed that the counterion is condensed on the sacran chain with raising the sacran concentrations. The decrease in the charge density of the sacran chain reduces the repulsive force between the chains and this would cause the helix transformation or gelation behavior. The chain conformation of sacran in pure water and the gelation mechanism are discussed in relation with the behavior of polyelectrolytes and liquid crystals. © 2013 American Physical Society.

DOI： 10.1103/PhysRevE.87.042607

Web of Science

Scopus

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Magnetic elastomers containing magnetic particles with a diameter of 235 mu m have been synthesized, and the magnetic response of the elasticity was investigated. The storage modulus for the magnetic elastomer with a volume fraction of 0.18 increased from 12.5 kPa to 2.43 MPa by applying a magnetic field of 500 mT. The relative change in the storage modulus was 194 times, which is higher than that of magnetic elastomers containing small iron particles (ca. 58 times at 2.5 mu m). It was also revealed that the magnetic elastomer exhibited wide-range modulation of loss tangent by varying magnetic fields.

DOI： 10.1246/cl.2013.253

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

Multi-walled carbon nanotubes (MWCNTs) were well dispersed in an aqueous solution of the cyanobacterial polysaccharide, sacran, with an ultra-high molecular weight >10 million g/mol. MWCNTs powder was put into aqueous solutions of various polysaccharides including sacran and was dispersed under sonication. As a result of the turbidity measurement of the supernatant, it was found that sacran showed the highest MWCNT-dispersion efficiency of all the polysaccharides used here. Cryogenic transmission electron microscopic (Cryo-TEM) studies directly demonstrated the existence of MWCNTs in the supernatant, and high-resolution TEM observation revealed that MWCNTs covered by sacran chains made their efficient dispersion in water. Raman spectroscopy demonstrated the existence of MWCNT in dried sample from supernatant and the interaction between MWCNT and sacran. The ?-potential measurement of the dispersion indicated the negative surface charges of the sacran/MWCNT complexes. Then the MWCNT complexes were able to fabricate by ionic interaction; electrophoresis of the anionic complex formed the sacran/MWCNT gels on the anode while the droplet of sacran/MWCNT dispersion formed gel beads in the presence of the lanthanoid cations. (c) 2012 Wiley Periodicals, Inc.

DOI： 10.1002/bip.22129

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Bimodal magnetic hydrogels consisting of magnetic and nonmagnetic particles were synthesized, and the magnetic response to the dynamic modulus of the gels was investigated. The change in the storage modulus for magnetic gels containing only magnetic particles exhibited 0.9 MPa by applying a magnetic field of 500 mT. The change in the storage modulus kept a high value although the magnetic particles were replaced with nonmagnetic particles by 34%. It can be considered that the magnetic interaction extends to the length of 4 to 6 microns via 2 or 3 nonmagnetic particles.

DOI： 10.1246/cl.2013.50

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Magnetism, dynamic viscoelasticity, mechanical property, and durability of magnetic elastomers consisting of polyurethane and carbonyl iron particles were investigated. Magnetic measurements revealed that the magnetic permeability of the magnetic elastomers can be explained by the linear combination of the magnetic permeability of magnetic particles and polyurethane. Dynamic viscoelastic measurements showed that the magnetic particles are randomly dispersed in the elastomer. On applying a magnetic field of 500 mT, the magnetic elastomers demonstrated a drastic change in the dynamic modulus; the storage modulus increased from 6.5 kPa to 1.6 MPa, and the loss modulus increased from 3.6 kPa to 0.16 MPa. This drastic change in the dynamic modulus was observed at all frequencies from 0.01 Hz to 3 Hz. The critical volume fraction showing the transition from a random dispersion to a chain structure decreased significantly with the magnetic field. Compression tests revealed that the magnetic elastomers exhibited high mechanical toughness with high breaking strain exceeding 0.8. Durability tests showed the magnetoviscoelastic behavior of the magnetic elastomers was maintained for 1.5 years after the synthesis without degradation.

DOI： 10.1039/c2sm26717a

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Physics Publishing  

Walking is one of the most popular activities and a healthy aerobic exercise for the elderly. However, if they have physical and / or cognitive disabilities, sometimes it is challenging to go somewhere they don't know well. The final goal of this study is to develop a virtual reality walking system that allows users to walk in virtual worlds fabricated with computer graphics. We focus on a haptic device that can perform various plantar pressures on users' soles of feet as an additional sense in the virtual reality walking. In this study, we discuss a use of a magnetic field sensitive elastomer (MSE) as a working material for the haptic interface on the sole. The first prototype with MSE was developed and evaluated in this work. According to the measurement of planter pressures, it was found that this device can perform different pressures on the sole of a light-weight user by applying magnetic field on the MSE. The result also implied necessities of the improvement of the magnetic circuit and the basic structure of the mechanism of the device. © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1742-6596/412/1/012036

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

The magnetoelastic behavior of bimodal magnetic elastomers consisting of magnetic particles, carbonyl iron, and nonmagnetic particles, zinc oxide, has been investigated by dynamic viscoelastic measurements. The storage modulus of bimodal magnetic elastomers increased under a magnetic field of 500 mT. The change in the storage modulus was enhanced by adding nonmagnetic particles at volume fractions above a certain volume fraction of 0.02, indicating the occurrence of stress transfer by a chain structure of magnetic particles via nonmagnetic particles. The critical volume fraction at 500 mT determined by percolation analysis was nearly independent of the diameter of nonmagnetic particles. However, at low magnetic fields below 160 mT, the critical volume fraction was found to decrease with the particle diameter. Substituting magnetic particles with nonmagnetic ones, the change in the storage modulus of bimodal magnetic elastomers monotonically decreased with the substitution ratio of magnetic particles. The mechanism of the enhanced magnetoelastic response for bimodal magnetic elastomers is discussed.

DOI： 10.1039/c3sm51836a

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The giant anionic polysaccharide "sacran", which is composed of 6-deoxyhexoses, pentoses, uronic acids as well as hexoses, showed hydrophobization and insolubilization phenomena in response to ultraviolet light irradiation. The sacran solution became turbid, and microparticles were formed by photoirradiation. To visualize the results of this photoreaction, anionic polysaccharide gels cross-linked by metal cations were used. As a result, we observed that sacrangels with trivalent metal ions gradually contracted depending on the photoirradiation energy. In contrast, alginate gels used as a comparison degraded instead of contracting. This photoshrinkage of the sacran gels may be attributed to the hydrophobization of uronic acid based on photodecarboxylation. We propose that sacran-metal ion gels can function as effective, photoresponsive gels.

DOI： 10.1021/bm301440e

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A new class of magnetoelastic gel that demonstrates drastic and reversible changes in storage modulus without using strong magnetic fields was obtained. The magnetic gel consists of carrageenan and carbonyl iron particles. The magnetic gel with a volume fraction of magnetic particles of 0.30 exhibited a reversible increase by a factor of 1400 of the storage modulus upon a magnetic field of 500 mT, which is the highest value in the past for magnetorheological soft materials. It is considered that the giant magnetoelastic behavior is caused by both high dispersibility and high mobility of magnetic particles in the carrageenan gel. The off-field storage modulus of the magnetic gel at volume fractions below 0.30 obeyed the Krieger-Dougherty equation, indicating random dispersion of magnetic particles. At 500 mT, the storage modulus was higher than 4.0 MPa, which is equal to that of magnetic fluids, indicating that the magnetic particles move and form a chain structure by magnetic fields. Morphological study revealed the evidence that the magnetic particles embedded in the gel were aligned in the direction of magnetic fields, accompanied by stretching of the gel network. We conclude that the giant magnetoelastic phenomenon originates from the chain structure consisting of magnetic particles similar to magnetic fluids.

DOI： 10.1021/jp3049372

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Anionic polysaccharide (PS) was extracted from Aphanothece stagnina biomaterials where trivalent metal ions were remarkably condensed from environmental water. Structural analyses indicated that the PS was considered to be a kind of sulfated rhamnoglucan-containing uronic acid at a composition of 23 mol% and that the total composition of anionic groups such as sulfate and carboxylate was 31 mol% to the monosaccharide residues. Since the PS was found to be a huge macromolecule with an ultra-high molecular weight (3.14x10(7) g/mol), the simple calculation indicated that about 9.5x10(4) anions exist on one chain of the PS. The electric conductivity of the highly anionic PS solutions indicated that the metal ions such as Ga(3+), La(3+), and Ca(2+) complexed ionically with PS chains. The PS formed the gels as a result of trivalent metal complexation, but the gelation behavior of the PS was different from that of the representative metal-complexable polysaccharide, alginate, in terms of the minimum gel formation concentration and the average molecular weight between cross-linking points.

DOI： 10.1007/s00396-011-2528-3

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Walking is a popular recreation activity. In addition, it is a mild and healthy exercise for the elderly. However, people suffering from physical and / or cognitive disorders have a difficulty in going out and walking in real environments. Therefore we have proposed a virtual walking system with a haptic device on feet. This system consists of visual, sound, and haptic devices to present various kinds of ambient information for users. The development of the haptic interface for feet soles is a main topic of this paper. We discuss a use of magnetic field sensitive elastomers (MSEs) as working materials for the device. In the previous report, we developed an electromagnet as a testbed of MSE and evaluated it performance. According to the measurement of planter pressures, this device can perform different pressures on soles by applying magnetic field. The result also implied necessities of the improvement of the magnetic circuit and basic structure for more feasible device. In this paper, we propose a new structure to control a frictional resistance force that is generated on the surface of the MSE and a metal pin. In addition, we propose to use this device as a single unit for the haptic device on feet. According to the compressive test of the unit, the maximum force that can be controlled with the unit is insufficient yet. However, it appears that we can control frictional force with the proposed structure. We also conducted a simulation to estimate required values of the performance for the unit. It is much higher than the current state of the unit. We have to improve the performance of the unit in the future.

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

A magnetic field sensitive elastomer (MSE) is a compound of magnetic particles and non-magnetic elastomers. This is a functional material whose elasticity can be adjusted with an external magnetic field. The final goal of this study is to develop a virtual walking system using a haptic device on soles of feet with the MSE. First, we measured the difference of planter pressures when subjects (3 young healthy students) stepped on two different types of floor (dot-type braille block and flat floor). The differences of the normalized pressures were about 2 similar to 4, and these values are one of the development goal of the device. Next, we designed an electromagnet and evaluate the difference of plantar pressure with / without magnetic field on the MSE. According to the results, the difference of the normalized pressure depended on the weight of subjects. The difference of the normalized pressure was 2.3 for a light subject. However, there were not clear differences for heavier subjects. We should consider the basic elasticity of the MSE to develop a practical device.

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

A magnetic field sensitive elastomer (MSE) is a compound of magnetic particles and non-magnetic elastomers. This is a functional material whose elasticity can be adjusted with an external magnetic field. The final goal of this study is to develop a virtual walking system using a haptic device on soles of feet with the MSE. First, we measured the difference of planter pressures when subjects (3 young healthy students) stepped on two different types of floor (dot-type braille block and flat floor). The differences of the normalized pressures were about 24, and these values are one of the development goal of the device. Next, we designed an electromagnet and evaluate the difference of plantar pressure with/without magnetic field on the MSE. According to the results, the difference of the normalized pressure depended on the weight of subjects. The difference of the normalized pressure was 2.3 for a light subject. However, there were not clear differences for heavier subjects. We should consider the basic elasticity of the MSE to develop a practical device. © 2012 IEEE.

DOI： 10.1109/BioRob.2012.6290673

Scopus

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Walking and traveling are popular recreation for the elderly in Japan. These activities are also mild activities exercises and have good effects for their health. However, people suffering from physical and / or cognitive disorders have a difficulty in going out and walking in real environments. Therefore we have proposed a virtual walking system with a haptic device on feet. This system consists of visual, sound, and haptic devices to present various kinds of ambient information for users. Especially, development of the haptic interface for feet soles is a new challenge. In this paper, we discuss a use of magnetic field sensitive elastomers (MSEs) as working materials for the device. We developed an electromagnet as a testbed of MSE and evaluated it performance. According to the measurement of planter pressures, this device can perform different pressures on soles by applying magnetic field. The result also implied necessities of the improvement of the magnetic circuit and basic structure for more feasible device. According to the experimental results on a dot-type braille block, a target level of the maximum plantar pressure was clarified. On the basis of these results, we designed a unit for the haptic device on feet.

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The effect of magnetic fields on the viscoelastic properties, the magnetorheological effect, of carrageenan gel containing iron oxide particles has been investigated using dynamic viscoelastic measurements under magnetic fields. The carrageenan concentration was varied in order to prepare magnetic gels with various storage moduli. Significant change in the storage modulus was not observed when the carrageenan concentration was 2 wt%; however, the magnetorheological effect appeared on decreasing the concentration. The maximum change in the relative storage modulus was 24 when the carrageenan concentration was 0.6 wt%. The loss tangents of the magnetic gels also altered in response to the magnetic field as well as the storage moduli. The relationship between the magnetorheology and the elasticity of magnetic gel is discussed.

DOI： 10.1088/0964-1726/20/12/124003

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WALTER DE GRUYTER GMBH  

Magnetic field effect on the elasticity was investigated for magnetic carrageenan gel when a shear and compressional deformation was applied to the gel. The magnetic carrageenan gel consists of carrageenan of a polysaccharide, and carbonyl iron particles. The dynamic viscoelastic measurement with shear strain revealed that the storage shear modulus of the gel increased from 1.0x10(4) to 2.3x10(6) Pa by applying a magnetic field of 320 mT. On the other hand, the compression measurement showed that the Young's modulus increased from 6.2x10(4) to 5.9x10(5) Pa. The relative changes in the modulus with respect to the original modulus were 230 for shear strain and 9.5 for compressional strain, respectively. This strongly indicates that the magnetic field effect on viscoelasticity strongly depends on the geometry of directions of magnetic field and strain. The effect of vibration suppression of the present gel tuned by magnetic field is also presented.

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

A new magnetorheological elastomer that demonstrates drastic and reversible changes in dynamic modulus in air was obtained. The magnetic elastomer consists of polyurethane and carbonyl iron particles. The magnetic elastomer with a volume fraction of 0.29 exhibited a reversible increase by factors of 277 of the storage modulus and 96 of the loss modulus upon a magnetic field of 500 mT. The elastomer underwent high mechanical toughness with a braking strain exceeding 0.8, and demonstrates the giant magnetorheological behavior for half a year after the synthesis without degradation.

DOI： 10.1039/c1py00033k

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The self-organization behavior of an extracellular polysaccharide (sacran) extracted from the cyanobacterium Aphanothece sacrum in response to lanthanoid ion adsorption was investigated. Consequently, cryogenic TEM images revealed that sacran could be cross-linked by Nd(3+) trivalent ions and formed a fibrous nanostructural network containing water. Furthermore, sacran adsorbed trivalent metal ions at a 3: 1 ratio, which was the theoretical ionic adsorption and showed more efficient adsorption than alginate based on electric conductivity titration. The critical gelation concentrations. C(g), where sacran formed tough gels upon metal ion binding were estimated. The C(g) for trivalent metal ions was lower than that for divalent ions, and the C(g) for lanthanoid ions was particularly low at 10(-3) to 10(-4) M, changing every four elemental numbers. The extracellular matrix of Aphanothece sacrum, sacran, may adsorb metal ions to create fibrous nanostructures that reinforce the jelly matrix.

DOI： 10.1021/bm101012u

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The cyanobacterial polysaccharide sacran, which contains carboxylate and sulfate groups, was extracted from Aphanothece sacrum, and the metal sorption behavior of sacran was investigated. Heterogels, where the sacran chains were trapped by polyvinyl alcohol networks, were prepared and immersed in NdCl(3) solutions to shrink and cloud due to Nd binding. These heterogels had the ability to sorb excessive amounts of Nd ions, more than the stoichiometric ratio of 1:3 (sacran anion/Nd). Furthermore, the sacran-containing gels sorbed Nd ions under highly acidic conditions below pH 2 more efficiently than alginate-containing gels. We speculated that the strong Nd condensation effect of the sulfate groups in sacran under the acidic conditions may enhance the Nd sorption to the carboxylate groups.

DOI： 10.1021/bm100231q

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

A magnetic-field-sensitive gel that demonstrates both drastic changes in dynamic modulus and high mechanical toughness was obtained. The magnetic gel consists of cross-linked poly(vinyl alcohol) (PVA), iron oxide particles, and water. The storage and loss shear moduli of the magnetic gel remarkably increased by applying a magnetic field, similarly to magnetic carrageenan gels. Compression revealed high mechanical toughness of the magnetic PVA gel and the maximum strain of 0.64 was achieved without inducing permanent strain.

DOI： 10.1246/cl.2010.550

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

A new class of magnetorheological gel that demonstrates drastic and reversible changes in dynamic modulus without using strong magnetic fields was obtained. The magnetic gel consists of carrageenan of polysaccharides and carbonyl iron particles. The magnetic gel with a volume fraction of 0.34 exhibited a reversible increase by factors of 500 of the storage modulus and 1200 of the loss modulus upon a magnetic field of 500 mT. We Postulate that the particle structural change by magnetic fields leads to the drastic change in the dynamic modulus.

DOI： 10.1246/cl.2009.922

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

Magnetorheological gels and elastomers demonstrate the phenomenon that viscoelastic properties such as elastic modulus change in response to magnetic fields. The magnetorheological materials consist of polymeric matrices and magnetic particles. As the viscoelastic properties can be controlled by the magnetic field, the materials have been used for active dampers that are able to control the attenuation of vibration. The magnetic effect on the elastic modulus has been extensively improved for the last ten years. This review is a short survey of past investigations and patents on magnetorheological gels and elastomers, and presents feature problems of the materials. © 2009 Bentham Science Publishers Ltd.

DOI： 10.2174/1874478810902020159

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Liquid crystallization of structural megamolecules in plants is very significant in understanding of biopolymer self-orientation and developing plant-derived functional materials. Cyanobacterial megamolecules, sacrans (molecular weight: 1.6 x 10(7) g/mol), are polysaccharides derived from the extracellular matrix of Aphanothece sacrum, and are observed as self-orienting micro rods longer than 3 mu m in dilute solution at c = 0.01 wt % by optical microscopes. Sacran chains form double helixes at c > 0.09 wt % and form huge domains (centimeter scale) of liquid crystals at c > 0.5 wt % which is quite low when compared to conventional liquid crystalline polysaccharides. Mesogenic helical chains of sacrans have extremely high aspect ratios of 1600 for highly persistent lengths of 32 mu m.

DOI： 10.1021/ma802829x

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER-VERLAG BERLIN  

We investigated the giant reduction in the dynamic modulus of magnetic gels with aligned particles. The magnetic gel is consisting of a kappa-carrageenan gel loaded with gamma-Fe2O3 particles with an aspect ratio of similar to 8. The magnetic particles were aligned by a weak magnetic field of 50 mT during gelation. The gels with aligned particles demonstrated giant reductions in the storage Young's modulus on the order of 10(6) Pa due to magnetization; however, no reductions in the storage modulus were observed for the gels with random particles. The storage modulus of gels with aligned particles did not follow the Halpin-Tsai equation above volume fractions of 0.01, indicating the heterogeneous dispersion of the magnetic particles; however, the modulus of the gels with random particles satisfied the equation at all volume fractions, suggesting the random dispersion of the particles. It was noted that the gels with aligned particles demonstrated enhanced nonlinear viscoelasticity and a large value of the loss tangent, while the gels with random particles exhibited weak nonlinear viscoelasticity and a small value of the loss tangent. This indicates that the magnetic particles form a particle network in the gel with aligned particles. It was also found that the magnetic gel with aligned particles did not undergo a marked reduction in the storage modulus when the magnetic field was applied in parallel with the alignment of magnetic particles. This strongly indicates that the giant reduction in dynamic modulus is caused by breaking the particle network developed in the magnetic gel.

DOI： 10.1007/2882_2009_23

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The particle dispersibility of barium ferrite and iron oxide magnetic particles in carrageenan gels was investigated, and the influence of the dispersibility on the giant reduction in the dynamic modulus of the gels was discussed. The gels containing barium ferrite demonstrated giant reductions in the storage Young's modulus on the order of 10(5) Pa due to magnetization; however, small reductions in the storage modulus of less than 10(4) Pa were observed for the gels containing iron oxide. The storage modulus of gels with barium ferrite did not follow the Krieger-Dougherty equation above volume fractions of 0.06, indicating the heterogeneous dispersion of the magnetic particles; however, the modulus of the gels with iron oxide satisfied the equation at all volume fractions, suggesting the random dispersion of the particles. It was noted that the gels with barium ferrite demonstrated enhanced nonlinear viscoelasticity and a large value of the loss tangent, while the gels with iron oxide exhibited weak nonlinear viscoelasticity and a small value of the loss tangent. Magnetic measurements indicated high values of remanent magnetization for barium ferrite and low values for iron oxide. After magnetization at 1 T, the magnetic gels with barium ferrite became elongated parallel to the magnetic field and shrunk perpendicular to the field. In contrast, the magnetic gels with iron oxide did not undergo a marked deformation. These results strongly indicate that the giant reduction in the storage modulus requires both enhanced nonlinear viscoelasticity and magnetostriction which originate from the particle dispersibility. The relationship between the dispersibility of magnetic particles and the giant reduction in the storage modulus is discussed using theological and morphological data.

DOI： 10.1021/jp805955j

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOCIETY APPLIED PHYSICS  

The magnetic field-induced elongation of magnetic gels consisting of poly(vinyl alcohol) (PVA) and magnetic particles was analyzed. The elongation increased as the concentration of magnetic particles increased, and inversely it decreased as the cross-linking density increased. We propose a simple theoretical expression of the elongation taking into consideration the elastic modulus of magnetic gels. We have fabricated a high-power actuator made of magnetic gels consisting of a thin magnetic-gel phase and a thick PVA-gel phase. A maximum strain of 33% was achieved while sustaining a constant stress of 1.3 kPa using a magnetic field of 900 mT. The magnetic gel showed a maximum stress of 6.8 kPa and a strain of approximately 10%. Magnetic gels consisting of two gel phases have great potential for application in practical actuators that can be driven by a magnetic field.

DOI： 10.1143/JJAP.47.7257

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

We investigated the rheological properties of a composite gel consisting of poly(vinyl alcohol) and aluminum hydroxide particles, and discussed the relation among nonlinear viscoelasticity, percolation and particles dispersibility. The dynamic viscoelastic measurements revealed that the storage modulus at volume fractions phi < 0.04 satisfied with the Krieger-Dougherty equation representing random dispersion of particles. The storage modulus did not show any nonlinear viscoelastic response at 0 < 0.04. However, the storage modulus at phi > 0.06 took a value which is far larger than that expected by the equation, indicating heterogeneous distribution of particles. Additionally, the nonlinear viscoelastic response was recognized clearly at 0 > 0.06, suggesting a partial contact between particles. The storage modulus at phi > 0.18 showed a further increase satisfied with the percolation theory, therefore, the volume fraction is considered to be the percolation threshold of 3-dimension. Microscopic observations of the gel showed a clear network with a mesh size of few mu m that is considered to be a partial network of particles. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.eurpolymj.2008.06.009

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A physically crosslinked poly(vinyl alcohol) (PVA) gel was synthesized from mixed aqueous solutions of PVA and sodium silicate (SS) using freeze/thaw techniques. The infrared spectroscopy, swelling and viscoelastic properties of the resultant gel have been investigated. The infrared spectrum of the resultant gel was as in the spectrum of PVA gel without SS. The resultant gel showed that the absorbing band due to stretching of hydroxyl groups shifted to a lower wave number, indicating the enhancement of hydrogen bonding between hydroxyl groups in PVA. Dynamic viscoelastic measurements showed that the storage modulus of the resultant gel was 1 order of magnitude higher than that of PVA gel without SS. The degree of swelling Q varied with the SS concentration c(SS) as Q similar to c(SS)(-1) (0.12 < v < 0.37). The storage modulus at 1 Hz E' changed by the degree of swelling Q satisfying with a power low as E' similar to Q(-3.8). Microphotographs of the gels in a dry state showed that PVA network developed extensively as increasing the SS concentration. These results obtained strongly indicate that the resultant gel consists from only PVA, not composites of PVA and SS. It can be considered that SS hastens the aggregation or crosslinking of PVA chains; as a result physically crosslinked gels with close network and high elasticity were obtained. Reswelling experiment showed that the degree of swelling by the reswelling for the resultant gel was approximately 10, which was less than 1/6 of the original value of the degree of swelling. (C) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.reactfunctpolym.2007.10.003

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：MATERIALS RESEARCH SOCIETY JAPAN-MRS-J  

We have investigated the elongational motion of magnetic gels under gradient magnetic fields. The magnetic gel was made from fine particles of iron oxide and a network of poly(vinyl alcohol) crosslinked by glutaraldehyde. The elongation increased with increasing the magnetic field strength up to 1200 mT. The elongation increased as increasing the concentration of magnetic particles; oppositely, it decreased as increasing the crosslinking density. It was found that the elongation can be explained by a classical theory of magnetism that the elongation is proportional to the product of magnetization and the field gradient. The effect of load on the elongation has been also investigated. The coefficient of the conversion from magnetic energy to mechanical one was estimated to be 10(-4)%, which is nearly independent of the load.

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：MATERIALS RESEARCH SOCIETY JAPAN-MRS-J  

We have investigated the electric conductivity and dielectric constant of an aqueous solution of polysaccharide, Aphanothece sacrum, that is called sacran. The molar conductivity at high concentrations obeyed Kohlrausch's law. The equivalent conductivity at infinite dilution was in good agreement with that of Na(+) ion in an aqueous solution. The complex dielectric constant epsilon* of the aqueous solutions was measured from 42 Hz to 5 MHz by an ac two-terminals method. The dielectric spectra of the aqueous solutions after subtracting the electrode polarization effect could be fitted by two Debye type relaxations. The low frequency relaxation and high frequency one appeared at 100 Hz and 100 kHz, respectively. The low frequency relaxation time for the aqueous solution of 2.0x10(-3) wt.% was determined to be 2.1 x10(-3) s. The contour length of the sacran was estimated to be similar to 5.5 mu m using the diffusion constant of Na(+) ion in a free medium. This value was in the same magnitude with the length evaluated from transmission electron microscopy and static light scattering experiments.

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

Accelerated drug release has been achieved by means of the fast rotation of magnetic gel beads. The magnetic gel bead consists of sodium alginate crosslinked by calcium chlorides, which contains barium ferrite of ferrimagnetic particles, and ketoprofen as a drug. The bead underwent rotational motion in response to rotational magnetic fields. In the case of bead without rotation, the amount of drug release into a phosphate buffer solution obeyed non-Fickian diffusion. The spontaneous drug release reached a saturation value of 0.90 mg at 25 minutes, which corresponds to 92% of the perfect release. The drug release was accelerated with increasing the rotation speed. The shortest time achieving the perfect release was approximately 3 minutes, which corresponds to 1/8 of the case without rotation. Simultaneous with the fast release, the bead collapsed probably due to the strong water flow surrounding the bead. The beads with high elasticity were hard to collapse and the fast release was not observed. Hence, the fast release of ketoprofen is triggered by the collapse of beads. Photographs of the collapse of beads, time profiles of the drug release, and a pulsatile release modulated by magnetic fields were presented.

DOI： 10.1155/2008/671642

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：EUROPEAN POLYMER FEDERATION  

A flexible fluid pump made of magnetic composite gels has been developed. The magnetic composite gel was sodium alginate or poly(vinyl alcohol) gel in which barium ferrite particles were dispersed. The pump consisted of a magnetic gel- rotor and a driving magnet. The rotor demonstrated the rotational motion in response to a rotational magnetic field generated by the driving magnet. The gel- rotor had the shape of a screw so as to deliver water efficiently. The diameter of the rotor was varied from 3.8 to 5.5 mm and the diameter of the tube for delivering water was kept as 6 mm. Flow rates pumped by the rotor increased with increasing the diameter, length, and rotation speeds of the rotor. The maximum flow rate of 34 ml/min was achieved when the rotation speeds was 5000 rpm. The rotor with a diameter of 300 mu m was also successfully synthesized, however the rotor did not deliver water in a microtube with a diameter of 500 mu m. Processing of the gel- rotor, and the efficiency of the water delivery are presented.

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

Magnetization effects on the dynamic modulus of a magnetic elastomer consisting of polyurethane and barium ferrite have been investigated. The complex modulus was measured before and after magnetization by dynamic viscoelastic measurements with a compressional strain. Giant reductions in storage modulus of similar to 105 Pa and in loss modulus of similar to 104 Pa were observed after magnetizing the elastomer at 1 T. The magnetic elastomer also showed a deformation with a strain of similar to 10-4 caused by the magnetization. The observed giant reduction in dynamic modulus can be ascribed to the large nonlinear viscoelastic response of the magnetic elastomer and the magnetization-induced deformation. Nonlinear viscoelastic responses, morphologies of magnetic particles, and deformation for the magnetic elastomer are discussed.

DOI： 10.1143/JJAP.46.4220

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We have investigated the transparency for visible light of a poly(vinyl alcohol) (PVA) aqueous solution in the presence of sodium silicates (SS). The transparency of the aqueous solution dramatically changed by varying temperature despite that neither aqueous solutions of PVA nor SS is sensitive to temperature. The aqueous solution showed a lower critical solution temperature (LCST) around 30 degrees C. The LCST depended on both concentrations of PVA and sodium silicate. Below the LCST, the transmittance was thermally irreversible. By a further increase in the temperature, the solution was separated into two phases consisting of a phase rich in solvent and that in solute; that is a coacervation. In the region of coacervation, the transmittance was thermally reversible. Reversible change in the transmittance was realized corresponding to stepwise temperature changes between 10 and 40 degrees C. A PVA gel swollen by the solution demonstrated transparency change in response to temperature changes as well as the solution. (C) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.matlet.2006.12.051

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：EUROPEAN POLYMER FEDERATION  

We have investigated the viscoelastic properties of poly( vinyl alcohol) (PVA) gels loaded with a polyelectrolyte particle of poly(styrene-co-sodium styrene sulfonate) to find the effect of electric charges on the storage modulus of the gel. The storage modulus decreased with increasing volume fraction of particles, and it was independent of the strain, indicating linear viscoelasticity. The viscoelastic properties of PVA gels containing non-charged particles of aluminium hydroxides were also studied. While the degree of swelling kept a constant value, the storage modulus largely increased with the volume fraction. PVA gels containing non-charged particles underwent a large nonlinear viscoelastic response suggesting the particles connect each other in the gel. Viscoelastic properties of the PVA gel loaded with charged and non-charged particles have also been discussed.

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：MATERIALS RESEARCH SOCIETY JAPAN-MRS-J  

We have fabricated the fluid valve in a fluid tube of 800 pm in diameter using magnetic gels. The magnetic gel was made from a network of poly(vinyl alcohol) crosslinked by glutaraldehyde and fine particles of iron oxide. When a weak magnetic field was applied to the valve, the valve came into a microtube and, as a result, a flow of water stopped. The valve opened and closed in response to the magnetic field generated by a permanent magnet. The valve worked well under the pressures of water from 0.3 MPa to 1.6 MPa.

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：MATERIALS RESEARCH SOCIETY JAPAN-MRS-J  

Effects of matrix on the giant reduction in storage modulus of magnetic gels have been investigated using agar and carrageenan gels. The complex modulus was measured before and after magnetization of the gel by dynamic viscoelastic measurements with a compressional strain. The agar magnetic gels showed a large nonlinear viscoelastic response and magnetically-induced deformation. The giant reduction in the storage modulus of similar to 10(5) Pa, and also in the loss modulus of similar to 10(4) Pa was observed for agar magnetic gels, as well as carrageenan one. The deformation due to magnetization seen in agar magnetic gels was larger than that in carrageenan by more than twice. Rheological data, deformation due to magnetization, and morphologies of magnetic particles have been discussed.

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Effects of magnetization on the complex modulus of kappa-carrageenan magnetic gels have been investigated. The magnetic gel was made of a natural polymer, kappa-carrageenan, and a ferrimagnetic particle, barium ferrite. The complex modulus was measured before and after magnetization of the gel by dynamic viscoelastic measurements with a compressional strain. The gels showed a giant reduction in the storage modulus of similar to 10(7) Pa and also in the loss modulus of similar to 10(6) Pa due to magnetization. The reduction increased with increasing volume fraction of ferrite, and it was nearly independent of the frequency. It was also found that the change in the modulus was nearly independent of the magnetization direction and irradiation time of the magnetic fields to the gel. The magnetic gels demonstrating the giant reduction in the dynamic modulus showed a large nonlinear viscoelastic response. It was observed that the magnetic gel was deformed slightly due to magnetization. The observed giant complex modulus reduction could be attributed to the nonlinear viscoelasticity and deformation caused by magnetization. Magnetism, nonlinear viscoelasticity, and effects of magnetization on the morphological and shape changes were discussed.

DOI： 10.1021/jp063494g

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We derive the analytic expression of elastic modulus for a gel containing magnetic particles with a magnetic dipole moment. The obtained elastic modulus is anisotropic and the modulus increases and decreases with the density of magnetic particle when the direction of strain is perpendicular and parallel to the direction of magnetization, respectively. This behavior is qualitatively in good agreement with previous experimental data [T. Mitsumata, et al., Macromol. Rapid Commun. 23, (2002) 178]. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physa.2006.02.040

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Electric field was found to facilitate the destruction of layer stacking and separation of silicate layers in polypropylene (PP)/layered silicate nanocomposites, resulting in the penetration of polymer chains into silicate galleries. In this study, we describe the real-time microstructural evolution of PP/clay nanocomposites under electric field investigated by in situ synchrotron wide-angle X-ray scattering (WAXS) analysis. We were able to identify two distinctive mechanisms for the formation of nanocomposites depending on the type of electric field. We observed that the exfoliation process prevails in the AC field, while the alignment of silicates parallel to the electric field predominates in the DC field. Dielectric relaxation analysis showed that the different mechanisms originate from different charge distributions of bound ions attached to the clay surfaces due to the applied electric field. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymer.2006.06.029

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Irradiating weak microwave to a poly(propylene) composite containing a small amount of single-walled carbon nanotubes (SWCNTs) enhances the storage modulus but has no effect on the loss modulus. We postulate that local melting and recrystallization of the polymer in the close vicinity of the SWCNT surface lead to better wetting, and larger contact areas for the improved elastic response.

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

Magneto-rheological effects of K-carrageenan magnetic gels have been investigated. The magnetic gel was made of a natural polymer of K-carrageenan and a ferromagnetic particle of barium ferrite. The complex modulus of the magnetic gel was measured by dynamic viscoelastic measurements with a compressional strain. It was observed that the magnetic gels showed giant storage modulus reduction similar to 10MPa before and after magnetization. The reduction increased with increasing the volume fraction of the ferrite and it reached 14.9 MPa at maximum. No volume change was observed during magnetization. Strain and frequency dependences of the dynamic modulus and a possible mechanism of the modulus reduction have been discussed.

Web of Science

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

We have developed a fluid pump using magnetic hydrogels synthesized by ferromagnetic fine particles and natural polymers. The pump is mainly consisted of a rotor made of the magnetic gel and a driving magnet. The driving magnet drives the rotor in a fluid tube without any physical contact. The rotor of the fluid pump rotates corresponding to the rotation rates of the driving magnet. The shape of the rotor was a screw so as to deliver water easily. Diameters of the rotor and the tube for delivering water were approximately 5.5mm and 6mm, respectively. Flow rates pumped by the rotor increased with increasing diameter, length of the rotor, and rotation rates. The maximum flow rates of 34 ml/min was achieved when the rotation rates was 5000 rpm. Factors affecting the flow rate of water will be presented.

Web of Science

researchmap

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

We have investigated the orientation effect of particles on the giant magnetorheological effect of magnetic gels. The magnetic gel is consisting of a κ-carrageenan gel loaded with magnetic particles with high aspect ratio ∼8. The magnetic particles were oriented by the uniform magnetic field with 50 mT during gelation. The storage modulus of the gel with oriented particles was much higher than that of the gel with random. Moreover, the gel with oriented particles showed a large non-linear viscoelastic response. These results strongly indicate that the magnetic particles are connected each other due to the orientation. For the gel oriented particles with 10wt%, the storage modulus after magnetization decreased by 2×105Pa, corresponding to 17% of the modulus before magnetization. When isotropic particles were used, no change in the modulus was observed at such low concentration of magnetic particles. Non-linearity and volume fraction dependence of the modulus will be presented.

Scopus

researchmap

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

We have investigated the effect of magnetization on the viscoelastic properties of magnetic gels. Effects of magnetization on the viscoelastic properties of agar-magnetic gels have been investigated. The magnetic gel is consisting of agar gel and barium ferrite fine particles. Concentrations of the magnetic particles were varied up to 60wt%. The storage modulus increased with increasing volume fractions of the magnetic particles. Increments in the modulus did not obey the theory that particles were randomly dispersed in matrices. It was considered that the barium ferrite particles make clusters in agar gels. In a higher concentration of barium ferrite, the gel showed non-linear viscoelastic response at very small strains with 10-4. It is probable that barium ferrite particles connect each other with very weak forces. The modulus change before and after magnetization showed ∼1×105 Pa only at 10wt% of ferrite concentration, and it increased with increasing the concentration. Increments in the modulus change were lower than that of carrageenan-magnetic gels. However, agar-magnetic gels have a feature that the giant modulus reduction occurs in lower ferrite concentrations. The observed giant modulus reduction would be originated from another mechanism of carrageenan magnetic gels.

Scopus

researchmap

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

Swelling properties of physical gels consisting of poly(vinyl alcohol) (PVA) and sodium silicate have been investigated. The physical gels were synthesized by freeze-thawing methods. The degree of swelling strongly depends on the concentrations of PVA and sodium silicate. As increasing the PVA concentration, the degree of swelling decreased. Above the PVA concentration with 2 wt%, the degree of swelling was independent of the PVA concentration. However, the degree of swelling depends on the concentration of sodium silicate when the PVA concentration is 1 wt%. Obtained gels showed high swelling degree and high elasticity compared to sodium silicate gels.

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Effects of magnetization on the complex modulus of kappa-carrageenan magnetic gels have been investigated. The magnetic gel was made of a natural polymer, kappa-carrageenan, and a ferromagnetic particle, barium ferrite. The complex modulus of the magnetic gel was investigated by dynamic viscoelastic measurements with a compressional strain. It was first observed that the magnetic gels showed giant storage modulus reduction;approximate to 10(7) Pa before and after magnetization. The reduction was nearly independent of the frequency, and it increased with increasing the volume fraction of the ferrite. The maximum reduction in the storage modulus reached 14.9 MPa which corresponds to 76.5% of the modulus before magnetization. It was also found that the change in the modulus was nearly independent of a magnetization direction. Magnetism and morphology of the magnetic gels were also presented.

DOI： 10.1002/marc.200500405

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

In this work, we have prepared bioartificial polymer blends using hyahuronate (HA) as a biological component and poly(vinyl alcohol)borax association (PVAs) as a synthetic component, and investigated the rheological properties as well as morphology of the blends. When plotted against the blend composition. the rheological properties showed both positive and negative deviation from the linear additive mixing rule depending on thermal history. The blend showed enhanced viscosity at the composition of 20 wt% of HA and 80 wt% of PVAs, when PVA was dissolved at high temperature. The viscosity enhancement was caused by the network formation of HA aggregates in the micrometer scale. In addition. the network Structure of HA aggregates was found to be fractal with the fractal dimension of 1.7. As PVA system also forms a network Structure in the nanometer scale between hydroxyl groups of PVA and borate anions, the blend system is unique in that it has network Structures in both micrometer and nanometer scales in one material. On the contrary. HA formed aggregates but not any network structure in the blend of the same composition but of the negative deviation. In Conclusion, we showed that HA/PVAs blend system may have diverse morphology as well its very broad spectrum of rheological properties, and could suggest that the rheology and morphology of HA/PVAs blends can be designed not only by controlling composition but also by controlling thermal and deformation history of the components. (c) 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymer.2005.05.089

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

We have investigated the rheological properties of poly(vinyl alcohol) gels containing aluminum hydroxide particles with the mean diameter of ∼1.4 μm. To find out the filler effect of the particle, the dynamic modulus of composite gels with the particle volume fraction φf&lt
0.23 was measured by dynamic viscoelastic measurements with a compressional strain. The storage modulus of composite gels below φf&lt
0.05 could be explained by Einstein's equation, however, an anomalous increase was observed above the particle volume fraction. It was also found that the storage modulus of composite gels with various cross-linking densities could be scaled by the particle volume fraction. Scanning electron microphotographs revealed that the composite gel had a network structure made of aluminum hydroxide with few microns. The network made of aluminum hydroxide would contribute the large increase in the storage modulus.

Scopus

researchmap

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

We have investigated the effect of magnetization on the viscoelastic properties of magnetic gels. The magnetic gel is consisting of κ-carrageenan gels loaded with magnetic particles. It was found for the gels that the storage modulus dramatically increased with increasing the particle concentrations. Non-linear viscoelasticity was observed at very small strains of 10-5, indicating the gel has a very weak structure made of magnetic particles. The storage modulus after magnetization decreased by 2×107Pa, corresponding to 76% of the modulus before magnetization. The change in the modulus increased with increasing the volume fraction of magnetic particles and the irradiation time of the magnetic field. It was also found that the modulus change occurs only 1s after applying magnetic field. Effects of gel matrices will be also presented.

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

The effects of magnetization direction on the complex modulus of magnetic gels, which consist of magnetized barium ferrite and poly vinyl alcohol, have been investigated. The modulus after magnetization showed anisotropy depending on the geometry of magnetization and strain direction. It was also confirmed that the modulus change occurred without volume change. This strongly suggested that the modulus change of magnetic gels originates not from a decrease in the volume of the magnetic gels but from the magnetic dipole interactions between ferrites dispersed in the gels.

DOI： 10.1143/JJAP.43.8203

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

We have investigated storage moduli of silicone gels containing barium titanate in the presence of dc electric fields. The gels containing barium titanate swollen by silicone oil showed a storage modulus reduction, i.e. negative electrotheological effect. Contrary, no negative electrorheological effect was observed in the unswollen gels and silicon gels without barium titanate. Swollen silicone gels and most of silicone/BaTiO3 gels obeyed empirical quadratic dependence in electric field strength. Although an apparent phase separation was not observed in the swollen gel, microscopic phase separation may occur due to the difference in electric conductivity between particles (similar to10(-10) S/cm) and silicone oil (10(-9) S/cm), as a result, the negative electrotheological effect appears. The effects of frequency, degree of swelling, and the field strength have been discussed. (C) 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymer.2004.03.056

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

We observed the negative electrorheological phenomenon on swollen silicone gels containing barium titanate. Contrary,no negative electrorheological effect was observed in unswollen silicone gels containing barium titanate and silicon gels without barium titanate. The change in storage modulus increase with increasing DC electric field strength. The effects of frequency, degree of swelling, and the field strength have been investigated.

DOI： 10.1002/marc.200300278

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

We synthesized the polyelectrolyte complex hydrogel consisting of chitosan, κ-carrageenan, and carboxymethyl cellulose sodium salt (NaCMC) and investigated the swelling properties of the gel varying with carrageenan/NaCMC compositions. In a lower composition of carrageenan, heterogeneous gels were obtained indicating strong electrostatic interactions among these polyelectrolytes. Oppositely, in a higher composition of carrageenan, a gelation did not occur. It was cleared that a homogeneity of the gel strongly depended on the carrageenan/NaCMC composition. The degree of swelling at the equilibrium decreased proportional to the carrageenan composition. The gels showed a maximum degree of swelling in the range of pH 11 - 12. The maximum degree of swelling discontinuously decreased with increasing the NaCMC composition and was independent of the composition at a higher composition of NaCMC. Swelling properties in pure water and in alkaline solutions were also affected by salt concentrations of each polyelectrolyte aqueous solutions. © 2003 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymer.2003.09.001

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jp027531p

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The storage moduli, shear moduli and surface morphologies of poly(vinyl alcohol) (PVA) and alumina hybrid hydrogels were investigated. The storage moduli of hybrid hydrogels with higher alumina contents were found to be 1.5 times higher than those of PVA gels. This increase in modulus might be attributed to the cohesion of alumina to the PVA network.

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The effects of magnetization direction on the longitudinal modulus of magnetic gels, which consist of magnetized barium ferrite and poly(vinyl alcohol), have been investigated using 10 MHz ultrasonic waves. The modulus change due to magnetization depends on both the crosslinking density and magnetization direction. The modulus change increased and decreased when the strain direction was perpendicular and parallel to magnetization, respectively.

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：John Wiley and Sons Ltd  

Amphiphilic polymer gels which can swell in both organic fluid and water have been widely investigated. We have discovered that this class of gels shows two special characteristics, i.e. the shape memory function and the spontaneous motion. The principle of the shape memory is based on a reversible order-disorder transition associated with interactions between the alkyl side chains of the stearyl acrylate units. This effect is completely different from the one of shape memory alloys. When the swollen gel is heated, its Young's modulus decreases by about three orders of magnitude, from 107 dyn/cm2 at 25°C to 104 dyn/cm2 at 50°C. These drastic changes in the mechanical properties enable the gel to show the shape memory function. Another feature of these gels is the spontaneous motion. The mechanism of the motion originates from the difference of surface tension between water and organic solvent that is pumped out by osmotic and hydrostatic pressures from the gel. Recently, we have succeeded to change the random motion to a translational one with a velocity of 77 mm/sec or rotational one with a maximum speed of 400 rpm. Motivated by this, electric power generator called "solvent-driven chemical motor" has been constructed. The generator produced an electric power with a maximum electromotive force of 15 mV and electric power of 0.2 μW. Copyright © 2001 John Wiley &amp
Sons, Ltd.

DOI： 10.1002/1099-1581(200101/02)12:1/2<136::AID-PAT76>3.0.CO;2-G

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACS  

Attempts have been made to control the spontaneous random motion of a tetrahydrofuran-swollen amphiphilic polymer gel on a water surface. By allowing the ejection of tetrahydrofuran through spouting holes, the gel showed an improved translational motion with a velocity of 77 mm/s or rotation with a rotation rate of 394 rpm. The controlled rotation showed an energy efficiency of 4.5×10-3%, which was 10 times of that of random motion. On the basis of the improved rotational motion of the gel, a generator consisting of a gel rotor equipped with a pair of permanent magnets and a solenoid coil has been constructed. The generator rotor which was 40 mm long, 6 mm wide, and 2 mm thick, produced an alternative electric power with an instantaneous electromotive force as high as 15 mV for a period of over 30 min. Such behaviors as the controlled motion, the spreading rate of tetrahydrofuran on the water surface, the crystallization and texture of gel surfaces, and the power generated have been described.

DOI： 10.1021/la990483o

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics Inc.  

We have investigated the magnetism and have measured the compressive modulus of magnetic fluid containing gels, called ferrogels, in the presence of magnetic field. No hysteresis was shown in the magnetization curve of the ferrogel suggesting a super paramagnetic response. The equilibrium compressive modulus of the ferrogel was measured up to 4 kOe and the modulus with field was much higher than that without field. The mean change in modulus increased with increasing magnetic field, and it saturates above 2 kOe. The mean and maximum change in modulus at 4 kOe was 31 and 71 Pa which corresponds to 19% and 46% increases of that without field, respectively. The change in modulus has been analyzed theoretically and is well explained in terms of the magnetism of ferrogels. © 1999 American Institute of Physics.

DOI： 10.1063/1.370626

Scopus

CiNii Article

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

Magnetic and transport properties of Ce5Ge3 and La5Ge3 have been studied. The magnetic susceptibility of Ce5Ge3 above 90 K is fitted with a Curie-Weiss law with an effective paramagnetic moment of 2.66μB and a paramagnetic Curie temperature of - 30.9 K. Arrott plot shows that Ce5Ge3 has a spontaneous magnetization below 6.4 K. The magnetization curve shows large hysteresis with remanent magnetic moment of 0.24μB and coercive field of 1.2 kOe at 2.0 K. The magnetization at 1.9 K reaches 0.9μB/Ce at 145 kOe and saturation behavior is not found even at this high field. The temperature dependence of the magnetic resistivity indicates that Ce5Ge3 can be classified as a dense Kondo system. © 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(98)01041-2

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

A solvent-driven chemical motor using amphiphilic polymer gel has been fabricated. The driving force of the gel originates from the surface tension of spreading organic fluid which is pumped out by osmotic and hydrostatic pressures in the gel. A tetrahydrofurane-swollen gel equipped with a spouting hole made a controlled translational motion with a velocity of 77 mm/s or rotational motion with a maximum speed of 400 rpm and a torque of 10-9-10-7Nm on the water surface. A generator to produce an electric power with a maximum electromotive force of 15 mV and electric power of 0.2 μW has also been constructed. The successful fabrication of gel motor may produce a new era of soft machine systems which work without pollution and unnecessary intermediates. © 1998 American Institute of Physics.

DOI： 10.1063/1.122505

Scopus

researchmap

Applicant：東洋ゴム工業株式会社

Application no：特願2013-029199  Date applied：2013.2

Announcement no：特開2014-156563  Date announced：2014.8

Patent/Registration no：特許第6013220号  Date issued：2016.9

J-GLOBAL

researchmap

Applicant：東洋ゴム工業株式会社

Application no：特願2013-029199  Date applied：2013.2

Announcement no：特開2014-156563  Date announced：2014.8

J-GLOBAL

researchmap

Applicant：東洋ゴム工業株式会社

Application no：特願2012-106713  Date applied：2012.5

Announcement no：特開2013-234244  Date announced：2013.11

Patent/Registration no：特許第6153702号  Date issued：2017.6

J-GLOBAL

researchmap

Applicant：東洋ゴム工業株式会社

Application no：特願2012-106713  Date applied：2012.5

Announcement no：特開2013-234244  Date announced：2013.11

J-GLOBAL

researchmap

Applicant：パナソニック株式会社

Application no：JP2011068261  Date applied：2011.8

Announcement no：WO2012-026332  Date announced：2012.3

J-GLOBAL

researchmap