Ryoichi Kishi

Fast responsive poly(N-sopropylacrylamide) hydrogels prepared by γ-ray irradiation

Abstract γ-ray irradiation of N-isopropylacrylamide (NIPAAm) monomer. solution resulted in the formation of the opaque poly (N-isopropylacrylamide) (PNIPAAm) gel having a microporous structure. The thermo-responsive properties of the microporous gel were the same as that of a homogeneous gel prepared by conventional methods. The gel swelled below and shrunk above the lower critical solution temperature (LCST) (33 °C). The rapid and reversible volume change was observed by changing temperature.

Separation of organic substances with thermoresponsive polymer hydrogel

Abstract Thermo-responsive polymer gel, poly(vinyl methyl ether) porous gel, was applied to the separation of organic substances in aqueous solution. Non-ionic surfactants were thermo-reversibly separated by the change of hydrophilic/hydrophobic balance of the gel. The separation technology may contribute to energy saving, environmental protection, etc.

Electrorheological Properties of Liquid-Crystalline Materials

Abstract Electrorheological properties of binary mixtures of liquid-crystalline polymer and low molecular weight liquid crystal were investigated. The viscosity of the liquid-crystalline mixture increased by application of DC electric field and recovered its original viscosity after the electric field was turned off. The effect appears above a field strength of 1.0 kV/mm, and the viscosity increases with the electric field strength. For shear rate 2 s−1 the viscosity was increased by approximately 5 times when 5.0 kV/mm was applied. Above nematic-isotropic transition temperature, electrorheological effect disappeared.

Electrorheological properties of liquid-crystalline materials containing liquid-crystalline polymer of various molecular weights and spacer lengths

Abstract Polymers with cyanobiphenyl groups (PCBAn) in their side-chains with different spacer lengths (n=2, 6, 11) and different molecular weights (Mw), were prepared. The phase behavior of the polymers and that of liquid-crystalline mixtures (LCMn) consisting of PCBAn and low-molecular weight liquid crystal, were observed. LCM2 and LCM6 showed liquid-crystalline property of nematic phase, while LCM11 showed liquid-crystalline property of smectic phase. The electrorheological properties of LCMn were investigated. The viscosity of LCMn increased upon application of a DC electric field, and the degree of increase was characteristic to each n value. LCM6 of different Mw showed nearly the same electrorheological behavior except for the LCM6 of lowest Mw, which displayed a large increase in viscosity upon application of the electric field.

NMR and DSC Observation of Thermotropic Nematic Liquid-Crystalline Polymer with Cyanobiphenyl Group in The Side Chain

Abstract The proton NMR spectra and DSC thermograms were observed with raising temperature for side chain type thermotropic liquid-crystalline polymer, poly(6-(4′-cyanobiphenyl-4-yloxy) hexylacrylate (PCBA). A pronounced variation was found for the NMR spectra and DSC heating curve depending on the thermal history applied on PCBA before the measurements. In the case of gradual cooling from the isotropic state to the solid state, DSC heating curve showed endothermic peak at the glass transition temperature. The line widths was taken as the parameter characterizing the NMR spectra and their temperature dependence was discussed. A qualitative interpretation on the observed NMR spectra was given in relation to the orientation of mesogenic group. The obtained endothermic peak was considered to come from the change in orientational behavior caused by the gradual cooling to the solid state.

Thermo-Responsive Polymer Gels

Polymer gels consist of a three-dimensional network of crosslinked polymers swollen in a liquid medium. Polymer gels are a kind of biomimetic material where solids coexist with liquids, like a living body. Recently, stimuli-responsive polymer gels have been attracting many researchers and been applied to a variety of fields, such as micro-machines, reversible separation, drug delivery systems, agriculture, etc. The gels reversibly change their shape and/or properties depending on several external physicochemical factors, such as photo-irradiation, temperature change, solvent composition, pH change, etc.

Order Formation Dynamics in the Early Stage of Melt Crystallization of Polymer Systems

Order formations dynamics during the crystallization processes of chain molecules have been studied by means of coarse-grained molecular dynamics simulations, mainly focusing on the early nucleation processes. In order to examine the nucleation and fluctuation dynamics in the early regime, we prepared dense melts of flexible chains which contained rigid extended chains as nucleating agents. A long induction time of the melt crystallization was observed for samples with a low nuclei concentration. For both each individual process and for the ensemble average, we present a precise analysis of the time evolution of the orientation order and crystallinity. A stretched exponential form expresses the time evolution curves for low nuclei concentration region. It was found that for the crystallization of chain molecules, the rigid extended chains play a significant role in the ordering dynamics.