Interparticle forces in a nematic liquid-crystal colloid have been directly observed by the dual beam laser trapping method with pN sensitivity. We introduce two different types of spatial distributions of forces, detected between the particles accompanied by hyperbolic hedgehog defects. These force distributions lead to specific particle arrangements, which are both stabilized by the balance of the orientational stress field of nematics. On the basis of these results, we propose novel artificial construction for multiparticle regular arrangements.
Dielectric segmental mode relaxation (the R-relaxation) was investigated for toluene solutions of poly(vinyl acetate) (PVAc) and for undiluted PVAc. The relaxation spectra in concentrated solutions were found to be much broad compared with those in the undiluted state and in dilute solution. It was also found that the relaxation spectra broadened with decreasing temperature near the glass transition temperature. For concentrated solutions, the correlation length of local heterogeneity (due to concentration fluctuation) was determined to be 1.0 nm by using small-angle X-ray scattering. On the basis of the assumption that the distribution of relaxation times in logarithmic scale is proportional to the magnitude of the heterogeneity, the temperature dependence of the broadness of loss curves can be explained. Thus, the broad dielectric relaxation spectra in concentrated solutions can be attributed to a local configurational irregularity of the polymer segments and the solvent molecules.
We have investigated the spontaneous formation of the regular quadrilateral defect array in cholesteric emulsions, composed of water, surfactants, and cholesteric liquid crystals. Both at the substrate surface and at the surfactant-coated droplet surface, a homeotropic anchoring is enforced to the adjacent liquid crystal. We observe nucleation of numerous point defects, in the cholesteric planar texture immediately after termination of shear to the emulsion, which leads to the formation of the regular defect array. We examined the temporal changes in density, size, and the positional correlation of point defects through the formation process of the defect array by means of two-dimensional fast Fourier transformation (2D FFT) image analysis. Two distinct stages were identified in the formation process; the early stage is the nucleation and growth process of point defects, and the late stage is the rearrangement process of point defects to the regular defect array. Water droplets destabilize the arrangement of cholesteric helix, which induces the transition from the shear-induced planar alignment to the homeotropic orientation.
We have investigated the rheological behavior of the quadrilateral defect array formed in cholesteric emulsions, which are composed of water, surfactants, and cholesteric liquid crystals. The defect array is spontaneously formed after stopping the shear to the cholesteric emulsions, between glass plates with a homeotropic anchoring surface. In the formation process of the defect array, Newtonian flow behavior was detected immediately after termination of the preshear; however, the shear yield stress appeared and was increasing with rest time, corresponding to the texture change. The maximum yield stress, which is detected in the well-developed defect array, tends to be proportional to the number of point defects, among the samples with different thicknesses. The stress-strain relation shows the elastic response in the low shear strain region, which obeys Hooke's law; therefore we have discussed the pitch dependence of the elastic constant per one point defect in the defect array. We proposed a simple model to estimate the yield stress of the defect array quantitatively, by considering that the shear deformation induces the compression and elongation of the cholesteric helix. The estimated yield values were in approximate agreement with the experimental results, which means that the shear stress propagates in the defect array through the liquidcrystalline order of the cholesteric helix between neighboring point defects separately anchored on upper or lower glass surfaces.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.