Masatoshi Kidowaki

Pressure‐Responsive Polymer Membranes of Slide‐Ring Gels with Movable Cross‐Links

Polymer membranes comprising slide-ring gels with movable cross-links exhibit a nonlinear pressure-dependence in the fluidic flow rate. The proportional constant between the flow rate and pressure significantly changes at a critical pressure. The slide-ring gels are promising polymer membrane materials, which would allow for the on-off control of fluid permeability using an imposed pressure.

Thermal amplification of photoinduced optical anisotropy of p-cyanoazobenzene polymer films monitored by temperature scanning ellipsometry

The in situ observation of thermal alteration of photoinduced optical anisotropy of ultrathin films of polymethacrylates having p-cyanoazobenzene side chains exhibiting amorphous, crystalline, and liquid-crystalline phases was performed by means of temperature scanning ellipsometry. Whereas photogenerated optical anisotropy of amorphous polymer films disappeared above glass transition temperature, the photoinduced anisotropy of films of liquid crystalline and crystalline polymer films was significantly amplified by heat treatment. In case of crystalline polymers, amplified optical anisotropy was maintained even at 300 °C.

Fabrication of mechanically improved hydrogels using a movable cross-linker based on vinyl modified polyrotaxane

This manuscript describes the preparation of new slide-ring gels by using a polyrotaxane as a cross-linker.

Orientational motions in mesogenic polyrotaxane and local mode relaxations of polymer segments in solid state polyrotaxane

In this study, we have investigated molecular fluctuations in a liquid crystalline polyrotaxane (CB5PR) consisting of poly(ethylene glycol) (PEG) and α-cyclodextrins (CDs) chemically modified with mesogenic cyanobiphenyl groups in solid state by dielectric spectroscopy. The results were compared with a hydroxypropylated polyrotaxane (HyPR) without mesogens. CB5PR showed a high-frequency relaxation mode, δ-relaxation due to the rotation of mesogenic groups at high temperature, whereas such a mode was not observed for HyPR. It was found that the activation energy of the rotational mode of mesogenic groups in CB5PR was considerably less than that in conventional side chain liquid crystalline polymers (LCPs). This indicated that the mesogenic groups around the polymer backbone in a solid-state PR rotated more easily than those in conventional LCPs, because mesogens bonded to cyclic CD in CB5PR can rotate independently of the rotational motion of the axis PEG. On the other hand, both CB5PR and HyPR exhibited broader relaxation processes at a much lower temperature around the glass transition of PEG, which was ascribable to the local molecular fluctuation of PEG. Our experimental results suggested that the local fluctuation of PEG in a PR was barely affected by the interaction between PEG and cyclic molecules, independently of the side chains around CD. This decoupling behavior is consistent with the low activation energy of the δ-relaxation in CB5PR.

Applicability of a particularly simple model to nonlinear elasticity of slide-ring gels with movable cross-links as revealed by unequal biaxial deformation

The strain energy density function (F) of the polyrotaxane-based slide-ring (SR) gels with movable cross-links along the network strands is characterized by unequal biaxial stretching which can achieve various types of deformation. The SR gels as prepared without any post-preparation complication exhibit considerably smaller values of the ratio of the stresses (σy/σx) in the stretched (x) and constrained (y) directions in planar extension than classical chemical gels with heterogeneous and nearly homogeneous network structures do. This feature of the SR gels leads to the peculiar characteristic that the strain energy density function (F) has no explicit cross term of strains in different directions, which is in contrast to F with explicit strain cross terms for most chemical gels and elastomers. The biaxial stress-strain data of the SR gels are successfully described by F of the Gent model with only two parameters (small-strain shear modulus and a parameter representing ultimate elongation), which introduces the finite extensibility effect into the neo-Hookean model with no explicit cross term of strain. The biaxial data of the deswollen SR gels examined in previous study, which underwent a considerable reduction in volume from the preparation state, are also well described by the Gent model, which is in contrast to the case of the classical chemical gels that the stress-strain relations before and after large deswelling are not described by a common type of F due to a significant degree of collapse of the network strands in the deswollen state. These intriguing features of nonlinear elasticity of the SR gels originate from a novel function of the slidable cross-links that can maximize the arrangement entropy of cross-linked and non-cross-linked cyclic molecules in the deformed networks.

Surface-Assisted Orientational Control of Discotic Liquid Crystals by Light

Abstract This paper reports photoalignment control of discotic liquid crystal (DLC), a pentakis-(phenylethynyl)benzene derivative, using a thin film of an azobenzene-containing polymer. The polymer films was irradiated with non-polarized light obliquely, subsequently annealed at 240°C and coated with a DLC solution to give a mono-domain texture of DLC films with excellent optical quality. Photopatterning of DLC films was achieved by imagewise irradiation of the polymer film at an oblique incident.

Static and dynamic light scattering studies on dilute polyrotaxane solutions

Static and dynamic light scattering measurements were performed for dilute polyrotaxane solutions in different types of solvent systems, i.e. dimethylacetamide (DMAc) or dimethylformamide (DMF) containing 1-6 wt% lithium chloride (LiCl), 1 M aqueous sodium hydroxide (NaOH) and dimethylsulfoxide (DMSO). No aggregation of the polyrotaxane in DMF/LiCl was confirmed in the present study. Radius of gyration of the dissolved polyrotaxane was largest in NaOHaq., followed by values in amide solvents/LiCl and that in DMSO, and was probably dominated not by Coulombic repulsion but by the mutual affinity between solvent and polyrotaxane. Ratio of radius of gyration to hydrodynamic radius suggested the flexible random-coiled conformation in DMSO and relatively more extended, semi-flexible ones in amide solvents/LiCl and NaOHaq. The obtained values of second virial coefficient and weight average molecular weight seemed to be affected by a potential change in differential refractive index increments, caused by selective macrocationization or ionization.

Thermal Properties and Microstructures of Methylated Polyrotaxane Solutions

Aqueous solutions of polyrotaxanes consisting of poly(ethylene glycol) and methylated alpha-cyclodextrins (alpha-CD) were studied by means of differential scanning calorimetry (DSC), dynamic light scattering, and X-ray diffraction in order to investigate the effect of the degree of methylation on thermoresponsive behavior. Polyrotaxanes with a degree of methylation higher than 50% had a lower critical solution temperature (LCST) and showed reversible associations and dissociations in water. In the transmittance measurements, the cloud point of methylated polyrotaxanes (MePR) shifted to a lower temperature with an increase in the degree of methylation. The heating curve obtained by DSC for the nearly permethylated polyrotaxane showed one broad endothermic peak that was associated with the microcrystallization of methylated CDs by hydrophobic interactions. On the other hand, the DSC profiles for partially methylated polyrotaxanes had several endothermic peaks, indicating multiple phase transitions of the MePR solutions. The results imply that the thermal properties of the MePR-water system are significantly affected by not only the methyl groups on alpha-CDs but also by the remaining hydroxyl groups.

Synthesis and Langmuir-Blodgett (LB) film properties of functional α,ω-diamine amphiphilic materials

We have investigated the synthesis and ultrathin film forming properties of α,ω-diamine derivatives. The amphiphiles were synthesized as precursors to the formation of ionene polymers. Two materials were investigated: oligothiophene and azobenzene functional groups. These type of materials are of great interest for the preparation of ultrathin film layers with applications for photochemical regulation of liquid crystal (LC) orientation, optical storage media, and electroluminescent displays. Azobenzene and its derivatives are well known photochemical systems exhibiting the reversible cis-trans photoisomerization. Conjugated oligothiophene derivatives, exhibit interesting optical and electronic properties for applications such as light emitting diodes (LED)s, Schottky diodes, and thin film field-effect transistors (TFT). The two amphiphiles behaved very differently as Langmuir monolayers and LB films. Dye aggregation was observed with the azobenzene derivatives compared with the oligothiophenes.

In-Situ Observation of Thermal Amplification of Photogenerated Optical Anisotropy of Films of Azobenzene Polymers

Thin films of polymers containing p -cyanoazobenzene side chains were studied to reveal its applicability for optical storage media, surface grating optics and aligning films for liquid crystal (LC) display devices. We followed the generation of optical anisotropy of LPLirradiated films of three polymethacrylates with azobenzene side chains exhibiting amorphous, crystalline and liquid-crystalline natures during heat treatment by mean of an ellipsometry and polarized UV-visible spectroscopy. Whereas photogenerated optical anisotropy of amorphous polymer films disappeared above glass transition temperature, the photo-induced anisotropy of films of liquid crystalline and crystalline polymer films was significantly amplified by heat treatment. In case of crystalline polymers amplified optical anisotropy was maintained even at 300°C whereas partial decomposition was observed.