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On the human face, the lips are one of the most important anatomical elements, both morphologically and functionally. Morphologically, they have a significant impact on aesthetics, and abnormal lip morphology causes sociopsychological problems. Functionally, they play a crucial role in breathing, articulation, feeding, and swallowing. An apparatus that can accurately and easily measure the elastic modulus of perioral tissues in clinical tests was developed, and its measurement sensitivity was evaluated. The apparatus is basically a uniaxial compression apparatus consisting of a force sensor and a displacement sensor. The displacement sensor works by enhancing the restoring force due to the deformation of soft materials. Using the apparatus, the force and the displacement were measured for polyurethane elastomers with various levels of softness, which are a model material of human tissues. The stress measured by the developed apparatus increased in proportion to Young’s modulus, and was measured by the compression apparatus at the whole region of Young’s modulus, indicating that the relation can be used for calibration. Clinical tests using the developed apparatus revealed that Young’s moduli for upper lip, left cheek, and right cheek were evaluated to be 45, 4.0, and 9.9 kPa, respectively. In this paper, the advantages of this apparatus and the interpretation of the data obtained are discussed from the perspective of orthodontics.

The adenosine A2A receptor antagonist/inverse agonist, KW-6356 has been shown to be effective in Parkinson's disease (PD) patients as monotherapy and as an adjunct therapy to L-3,4-dihydroxyphenylalanine (L-DOPA)/decarboxylase inhibitor. However, the effects of KW-6356 combined with L-DOPA on anti-parkinsonian activity and established dyskinesia has not been investigated in preclinical experiments. We examined the effects of combination of KW-6356 with L-DOPA in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated common marmosets. Oral administration of KW-6356 (1 mg/kg) enhanced the anti-parkinsonian activities of various doses of L-DOPA (2.5–10 mg/kg). In MPTP-treated common marmosets primed with L-DOPA to show dyskinesia, KW-6356 (1 mg/kg) also enhanced the anti-parkinsonian activities of various doses of L-DOPA (1.25–10 mg/kg) but not dyskinesia. Chronic co-administration of KW-6356 (1 mg/kg) with a low dose of L-DOPA (2.5 mg/kg) for 21 days increased the degree of dyskinesia induced by the low dose of L-DOPA, but the amplitude of dyskinesia induced by combined administration of KW-6356 (1 mg/kg) with L-DOPA (2.5 mg/kg) was lower than that induced by an optimal dose of L-DOPA (10 mg/kg). These results suggest that KW-6356 can be used to potentiate the effects of a wide range of L-DOPA doses with a low risk of dyskinesia for the treatment of PD.

The effects of water absorption on the electric resistivity and dielectric constant of polyimide (PI) and poly(ethylene terephthalate) (PET) were investigated, and the mechanism of deterioration in electrical insulation properties was discussed. The polyimides are poly(oxydianiline pyromellitimide) (PMDA–ODA) and poly(para-phenylene diamine biphenyltetracarboxydiimide) (BPDA–PDA). These polymer films were immersed in pure water for various immersion times at room temperature, and the water absorption ratio was evaluated. The electric resistance for these films was measured at room temperature using a high-resistance meter, and the dielectric constant at room temperature was measured using an LCR meter in a frequency range of 200 kHz to 2 MHz. The absorption ratios at equilibrium absorption for PMDA–ODA, BPDA–PDA, and PET were 2.7, 2.5, and 0.5%, respectively. The critical volume fraction of the percolation threshold of electric conductivity due to water absorption was 0.034 for both PMDA–ODA and BPDA–PDA. On the other hand, PET did not show a significant decrease in the resistivity. For both PIs and PET, the dielectric constant observed could be explained by a series model of the respective capacitances of pure water and polymer. Actually, the resistivity of samples cut from the edges of the film after water absorption was almost the same value as that in the dry state. These results suggest that the absorbed water molecules are not uniformly dispersed in the film but are localized at the edges of the film even after the absorption equilibrium has been reached.

The mechanical properties for paper sheets composited with glucose (Glc), methyl cellulose (MC), and carboxymethyl cellulose (CMC) were investigated. The paper composites were prepared by immersing paper sheets in aqueous solutions of these materials and drying at 100 °C for 30 min. The stress–strain curves for these paper composites were measured by a uniaxial tensile apparatus with a stretching speed of 2 mm/min. The breaking stress and strain for untreated paper were 24 MPa and 0.016, respectively. The paper composites demonstrated stress–strain curves similar to the untreated paper; however, the breaking point largely differed for these composites. The breaking strain and breaking stress for the Glc composite slightly decreased and those for the MC composite gradually increased with the concentration of materials composited. Significant increases in the mechanical properties were observed for the CMC composite. The breaking stress, breaking strain, and breaking energy for the 3 wt.% CMC composite were 2.0-, 3.9-, and 8.0-fold higher than those for untreated paper, respectively. SEM photographs indicated that the CMC penetrated into the inner part of the paper. These results strongly suggest that the mechanical improvement for CMC composites can be understood as an enhancement of the bond strength between the paper fibrils by CMC, which acts as a bonding agent. It was also revealed that the breaking strain, breaking stress, and breaking energy for the CMC composites were at maximum at the first cycle and decreased gradually as the immersion cycles increased.

The effect of the cooling rate on magnetorheological response was investigated for magnetic hydrogels consisting of carrageenan and carbonyl iron particles with a concentration of 50 wt.%. For magnetic gels prepared via natural cooling, the storage moduli at 0 and 50 mT were 3.7 × 104 Pa and 5.6 × 104 Pa, respectively, and the change in the modulus was 1.9 × 104 Pa. For magnetic gels prepared via rapid cooling, the storage moduli at 0 and 50 mT were 1.2 × 104 Pa and 1.8 × 104 Pa, respectively, and the change in the modulus was 6.2 × 103 Pa, which was 1/3 of that for the magnetic gel prepared by natural cooling. The critical strains, where G′ is equal to G″ on the strain dependence of the storage modulus, for magnetic gels prepared by natural cooling and rapid cooling, were 0.023 and 0.034, respectively, indicating that the magnetic gel prepared by rapid cooling has a hard structure compared to that prepared by natural cooling. Opposite to this, the change in the storage modulus at 500 mT for the magnetic gel prepared by rapid cooling was 1.6 × 105 Pa, which was 2.5 times higher than that prepared by natural cooling. SEM images revealed that many small aggregations of the carrageenan network were found in the magnetic gel prepared by natural cooling, and continuous phases of carrageenan network with large sizes were found in the magnetic gel prepared by rapid cooling. It was revealed that magnetic particles in the magnetic gel prepared by rapid cooling can move and form a chain structure at high magnetic fields by breaking the restriction from the continuous phases of carrageenan.

During the storage of celluloid pictures for animation films over half a century, an interleave paper adhered to acrylic paint. The purpose of this study is to establish a methodology to cleanly remove the paper from the paint. A layered film, a replica of the celluloid pictures, adhered with paper was prepared and immersed in water or ethanol. The effect of these solvents on the peeling behavior was investigated using a peel test. The maximum peel force for the dry layered film in was distributed at ~0.5 N, independently of the peel speed. The peel force was significantly reduced after the layered film was immersed in pure water or ethanol. A morphological observation revealed that the dry paper was peeled off via the cohesive failure of the paper. After the layered film was immersed in pure water, the paper was also peeled off via cohesive failure. The layered film immersed in ethanol was peeled off at the paper/paint interface. To clear the effect of the volume change in the paint on peel behavior, the relative volume was determined via image analysis. The relative volume of paint was 1.56 in pure water and 1.37 in ethanol. It can be considered that the large difference in the volume of paint induces a large shear stress at the paint/paper interface.

The effect of carrageenan concentration on the magneto-rheological effect of magnetic gels with a magnetic particle concentration of 50 wt.% was investigated under a magnetic field of 50 mT by dynamic viscoelastic measurements. The change in the storage modulus for magnetic gels due to the magnetic field was 3.0 × 103 Pa at a carrageenan concentration of 1.0 wt.% and increased with the concentration. The modulus change showed a maximum of 2.3 × 104 Pa at ~2.0 wt.% and became lower at higher concentrations. This is an interesting phenomenon, which was first observed in this study. The critical strain, the strain where the storage modulus intersects the loss modulus in the strain dependence of the modulus, was much higher than that for carrageenan gels, indicating a strong interaction between the magnetic particles and carrageenan. At 0 mT, the critical strain for the magnetic gels increased remarkably with decreasing the concentration, indicating that magnetic gels have a structure that does not flow easily at concentrations below 1.75 wt.%. It is considered that the structure hardly flows, hindering the movement of particles. At high concentrations, the SEM photographs showed both a particle network of magnetic particles and a dense carrageenan network. It can be considered that the movement of magnetic particles was hindered due to these factors at high concentrations.

BACKGROUND:Elevated parathyroid hormone (PTH) levels in secondary hyperparathyroidism (SHPT) lead to vascular calcification, which is associated with cardiovascular events and mortality. Increased PTH production is caused by the excessive proliferation of parathyroid gland cells, which is accelerated by abnormal mineral homeostasis. Evocalcet, an oral calcimimetic agent, inhibits the secretion of PTH from parathyroid gland cells and has been used for the management of SHPT in dialysis patients. We observed the effects of evocalcet on ectopic calcification and parathyroid hyperplasia using chronic kidney disease (CKD) rats with SHPT. METHODS:CKD rats with SHPT induced by adenine received evocalcet orally for 5 weeks. The calcium and inorganic phosphorus content in the aorta, heart and kidney was measured. Ectopic calcified tissues were also assessed histologically. To observe the effects on the proliferation of parathyroid gland cells, parathyroid glands were histologically assessed in CKD rats with SHPT induced by 5/6 nephrectomy (Nx) after receiving evocalcet orally for 4 weeks. RESULTS:Evocalcet prevented the increase in calcium and inorganic phosphorus content in the ectopic tissues and suppressed calcification of the aorta, heart and kidney in CKD rats with SHPT by reducing the serum PTH and calcium levels. Evocalcet suppressed the parathyroid gland cell proliferation and reduced the sizes of parathyroid cells in CKD rats with SHPT. CONCLUSIONS:These findings suggest that evocalcet would prevent ectopic calcification and suppress parathyroid hyperplasia in patients with SHPT.

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 mm 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.

The relationship between rheological features in the absence of a magnetic field and magnetic response was investigated for κ-carrageenan magnetic hydrogels containing carbonyl iron particles. The concentration of carrageenan was varied from 1.0 to 5.0 wt%, while the concentration of carbonyl iron was kept at 70 wt%. The magnetic response revealed that the change in storage modulus ΔG′ decreased inversely proportional to the carrageenan concentration. A characteristic strain γ1 where G′ equals to G″ was seen in a strain range of 10−3. It was found that ΔG′ was inversely proportional to the characteristic stress at γ1. Another characteristic strain γ2 where the loss tangent significantly increased was also analyzed. Similar to the behavior of γ1, ΔG′ was inversely proportional to γ2. The characteristic stresses at γ1 and γ2 were distributed at 80–720 Pa and 40–310 Pa, respectively. It was revealed that a giant magnetorheology higher than 1 MPa can be observed when the characteristic stresses at γ1 and γ2 are below approximately 240 Pa and 110 Pa, respectively.

The magnetorheological response for magnetic elastomers containing carbonyl iron (CI) particles with a diameter of 6.7 μm coated with poly(methyl methacrylate) (PMMA) was investigated to estimate the diameter of secondary particles from the amplitude of magnetorheological response. Fourier-transformed infrared spectroscopy revealed that the CI particles were coated with PMMA, and the thickness of the PMMA layer was determined to be 71 nm by density measurement. The change in the storage modulus for magnetic elastomers decreased by coating and it was scaled by the number density of CI particles as ΔG~N2.8. The diameter of secondary particle of CI particles coated with PMMA was calculated to be 8.4 μm. SEM images revealed that the CI particles coated with PMMA aggregated in the polyurethane matrix.

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 μm 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 × 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 × 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 × 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.

The rheopectic behavior of sacran aqueous solutions, a natural giant molecular polysaccharide with a molecular weight of 1.6 × 107 g/mol, was investigated. When a low shear was applied to 1.0 wt.% sacran solution, the shear viscosity increased from 7.2 to 34 Pa·s. The increment in the viscosity was enhanced as the shear rate decreased. The shear viscosity was independent of the time at a shear rate of 0.8 s−1; simultaneously, thixotropic behavior was observed at shear rates higher than 1.0 s−1. A crossover was observed at 0.15 wt.% for the concentration dependence of both the viscosity increase and zeta potential, which was the vicinity of the helix transition concentration or gelation concentration. It was clear that the molecular mechanism for the rheopexy was different at lower and higher regions of the crossover concentration.

In order to improve the running performance of a railway vehicle, the authors developed the axle box suspension with the magnetic elastomer. The magnetic elastomer is composed of magnetic particles and the elastomer such as synthetic rubber. This material is characterized by its hardness variation depending on the magnetic field. In this paper, the authors synthesized the bimodal magnetic elastomer containing nonmagnetic particles. In a characteristic test, the authors confirmed that Young's modulus of the magnetic elastomer changed in the range of about 2.2 times depending on the magnetic field. Moreover, the authors carried out a running test on a test line of the MIHARA Test Center. The authors confirmed that the axle box suspension with the magnetic elastomer were able to secure the running stability at 70 km/h without causing an unstable state. In addition, the authors carried out a running test on a test line of the Railway Technical Research Institute. The authors confirmed that the axle box suspension with the magnetic elastomer were able to reduce the outer lateral force of a leading wheelset.

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.

The adenosine A2A-receptor antagonist istradefylline decreases OFF time in patients with Parkinson’s disease who are already treated with optimal doses of dopaminergic medication but can cause an increase in non-troublesome dyskinesia. Preclinical experiments have shown that A2A antagonists are most effective in potentiating motor function when combined with submaximal doses of l-DOPA. However, the effects of combining istradefylline with sub-optimal l-DOPA treatment on established dyskinesia have not been studied. We now examine the effects of acute and repeated administration of istradefylline on dyskinesia in MPTP-treated common marmosets previously primed to exhibit involuntary movements by prior exposure to l-DOPA. In these animals, single dose acute oral administration of istradefylline (10 mg/kg) enhanced and prolonged the anti-parkinsonian effects of a sub-optimal dose of l-DOPA (2.5 mg/kg). The chronic co-administration of istradefylline (10 mg/kg) with l-DOPA (2.5 mg/kg) for 21 days did not worsen the severity of existing dyskinesia. Rather, the severity of dyskinesia tended to be reduced over the 21-day treatment period. These results suggest that istradefylline can be used to potentiate the effects of sub-optimal doses of l-DOPA in the treatment of Parkinson’s disease without causing or worsening dyskinesia. Keywords:: anti-parkinsonian, adenosine A2A-receptor antagonist, l-DOPA, dyskinesia, MPTP

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.

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.

The morphology of magnetic particles with a size of 7.0 μm 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.

We fabricated a mono-link using bimodal magnetic elastomers that demonstrate drastic changes in the elastic modulus by magnetic fields. The magnetic elastomer is bimodal consisting of large magnetic particles and nonmagnetic fine particles. The storage modulus for bimodal magnetic elastomers was altered from 2.2 × 105 to 1.7 × 106 Pa by a magnetic field of 500 mT. Compression tests up to a strain of 20% also revealed that the on-field stress for the bimodal magnetic elastomer was 1.24 times higher than the off-field stress. The bimodal magnetic elastomer was synthesized for the mono-link and was mounted on the bogie of a railway vehicle. A running test exhibited that the wheel lateral force was reduced by 20% by applying a magnetic field of 390 mT.

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%.

The effect of sonication time on the storage modulus and particle morphology for magnetic elastomers was investigated by dynamic viscoelastic measurements and morphological studies. An ultrasonic wave using a homogenizer was irradiated to magnetic liquids containing 70 wt % carbonyl iron, for up to 30 min before cure. SEM photographs revealed that magnetic particles were randomly dispersed in the polyurethane matrix for magnetic elastomers with sonication. A parameter showing nonlinear viscoelasticity for magnetic elastomers with sonication decreased from 0.75 to 0.4, indicating that the aggregations of magnetic particles had been destroyed by the sonication. The storage modulus at 500 mT at the linear viscoelastic regime significantly increased with the irradiation time, reaching saturation after 10 min; this suggests an increase in the number of chains of magnetic particles by sonication, due to the random dispersion of magnetic particles. At high strains, the storage modulus at 500 mT increased by 8.9 kPa by sonication, indicating the number of chains of magnetic particles which were not destroyed by increased sonication. It was also found that the storage modulus for polyurethane elastomers without magnetic particles was not varied by sonication, suggesting that the polyurethane network was not broken. The effect of sonication time on the viscoelastic properties, and on the magnetorheological response for magnetic elastomers, is discussed.

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.

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 8.94×104Pa at 0mT and 1.65×105Pa 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. [ABSTRACT FROM AUTHOR]

The rheopectic behavior of sacran aqueous solutions, a natural giant molecular polysaccharide with a molecular weight of 1.6 × 107 g/mol, was investigated. When a low shear was applied to 1.0 wt.% sacran solution, the shear viscosity increased from 7.2 to 34 Pa·s. The increment in the viscosity was enhanced as the shear rate decreased. The shear viscosity was independent of the time at a shear rate of 0.8 s-1; simultaneously, thixotropic behavior was observed at shear rates higher than 1.0 s-1. A crossover was observed at 0.15 wt.% for the concentration dependence of both the viscosity increase and zeta potential, which was the vicinity of the helix transition concentration or gelation concentration. It was clear that the molecular mechanism for the rheopexy was different at lower and higher regions of the crossover concentration. [ABSTRACT FROM AUTHOR]

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 3.7mTs-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 10-2mT-1 at the maximum volume fraction of magnetic particles. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The effect of plasticizer content on the magnetic-field sensitivity for magnetic elastomers has been investigated while maintaining the concentration of magnetic particles at 70wt %. 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 3.7mTs-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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 0mT decreased with plasticizer content, whereas the storage modulus at 500mT 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. [ABSTRACT FROM AUTHOR]

Magnetic elastomers containing magnetic particles with a diameter of 235 μm 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 500mT. 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 μm). It was also revealed that the magnetic elastomer exhibited wide-range modulation of loss tangent by varying magnetic fields. [ABSTRACT FROM AUTHOR]

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 500mT. 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. [ABSTRACT FROM AUTHOR]