Electrical Actuation of Cholesteric Liquid Crystal Gels

We demonstrate that the cholesteric liquid crystal (CLC) gels with a global helical variation in their orientation exhibit the pronounced electro-optical and electromechanical effects under an unconstrained geometry. A sufficiently high electric field imposed along the helical axis drives a finite elongation exceeding 30% along the field axis, as well as a finite redshift of the selective reflection band which is opposite to the blueshift often observed for the conventional CLCs and the in situ polymer stabilized CLCs under an electric field

Strain-Driven Swelling and Accompanying Stress Reduction in Polymer Gels under Biaxial Stretching

Strain-driven swelling and the accompanying stress reduction in polymer gels are investigated experimentally under general biaxial deformation, with strain being varied independently in two directions. The equilibrium degrees of strain-induced swelling and stress reduction depend markedly on both the magnitude and the type of the imposed deformation. When subjected to a constant elongation in one direction, the strain-induced swelling in biaxial stretching increases with an increase in the elongation in the other direction: When a gel is equibiaxially stretched by a factor of 2, the equilibrium volume is approximately 2.5 times greater than the initial volume. The degree of stress reduction in the direction of the smaller imposed strain is greater than that in the other direction: The stress in the constrained direction of planar extension is reduced by more than 40%. The time course of the stress reduction is governed by a diffusion process, i.e., the dynamics of swelling. The main features of the experimental results are satisfactorily explained by a classical theory for swelling of gels

Beads-on-String-Shaped Poly(azomethine) Applicable for Solution Processing of Bilayer Devices Using a Same Solvent

Solvent-based deposition techniques for fabrication of organic field-effect transistors (OFETs) generally require orthogonal solvents for deposition of a conjugated polymer layer on a polymer gate insulator layer. Here, we found significantly reduced dissolution rate of the polymeric film in the same solvent after casting a homegeneous polymerization solution of <i>para</i>-bis­(3-aminopropyl)­hexaisobutyl-substituted T₈ cage (<b>1</b>) with terephthalaldehyde. The limited dissolution rate in the solvent provided enough chance for fabrication of a regioregular poly­(3-hexylthiophene-2,5-diyl) (P3HT) layer on the present polymer films without using an orthogonal solvent. The rheological properties indicate that physical interaction between the polymer chains provides the significantly reduced dissolution rate after the deposition onto a substrate without any cross-linking treatments

Application of a Strained Natural Rubber at High Temperatures

Robustness of the natural rubber (NR) crystal at high temperatures is important because vehicle tires are easily subjected to high temperatures due to friction. To understand the robustness of crystals in the strained NR, as its plausible application to high temperatures, changes in the following structural parameters as a function of temperature were examined in this study by conducting two-dimensional wide-angle X-ray diffraction measurements: crystal lattice constants (a, b, c, and β), unit cell (volume, thermal expansivity, and orientation factor), degree of crystallinity, and crystallite (size, volume, and number density in the strained NR specimen). As a result for a vulcanized NR specimen subjected to a constant strain of 6, thermal shrinkage of the c-axis length was found in the heating process, while both a- and b-axis lengths were found to increase with an increase in the temperature. Furthermore, the volume of the crystal lattice was found to increase with the temperature, while the orientation degree of the crystal lattice remained unchanged. The degree of crystallinity was found to gradually decrease with temperature from the beginning of heating. As for the crystallite, the size along the stacking direction of the (200), (120), and (201) planes decreased with temperature, while that of the (002) plane (i.e., along the c-axis direction) was found to increase. These results indicate that crystallites grow in the NR main chain direction, while they are subjected to melting in the other perpendicular directions upon heating. However, it was found that the crystallite volume and the number density of crystallites in the strained NR specimen continuously decreased with the increasing temperature. The thermo-reversibility of all the structural parameters was also examined experimentally