%0 Journal Article
%T Polar Liquid Crystal Elastomers Cross Linked Far from Thermodynamic Phase Transitions: Dislocation Loops in Smectic Clusters
%A Yusril Yusuf
%A Shohei Yamaguchi
%A Shinya Kawano
%A Hirotaka Okabe
%A Simon Krause
%A Heino Finkelmann
%A P. E. Cladis
%A Shoichi Kai
%J Advances in Condensed Matter Physics
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/752060
%X Nematic networks with three different concentrations of polar and nonpolar mesogens and the same concentration of a novel cross-linking agent give rise to unusual liquid single crystal elastomers (LSCEs) that are transparent monodomain nematic networks with smectic clusters. The largest spontaneous length change is observed in the sample with 70£¿mol% of the polar mesogen which also has the highest glass transition temperature and smectic clusters with a slowly increasing but nearly constant layer spacing on cooling from 90¡ãC to 25¡ãC. X-ray scattering intensity from smectic clusters with layer spacings that monotonically increase on cooling first increases to a maximum at C corresponding to clusters of about 30 layers. Below , the scattering intensity decreases as the number of layers in a cluster decreases. To account for this surprising nonlinear behavior that correlates with nonlinear features of the networks¡¯ macroscopic spontaneous shape change and birefringence, a model is proposed where dislocations form in the layers at . Below , more dislocations form to break down the layer structure. The possibility of dislocation formation at independent of mesogenic concentrations is attributed to a conformational change in the crosslinker which is present at the same concentration in the three LSCEs. 1. Introduction Liquid crystal states of matter have long range orientational order characterized by a director, , which can be oriented anywhere in three-dimensional space. Liquid crystals are an example of a continuous medium where is defined everywhere in the sample except at line defects. Nevertheless, it is interesting to probe differences between low-molecular-weight nematic liquid crystals, familiar as the light switch in flat panel displays, and liquid crystal elastomers resulting when a low-molecular-weight liquid crystal is polymerized and cross linked in one process to make a polydomain liquid crystal elastomer (LCE) [1¨C5]. Particulary as, following polymerization and cross linking, monodomain LCEs where is locked in the sample can be prepared and studied [2, 4, 6, 7]. The resulting liquid single crystal elastomers (LSCEs) change their lengths significantly in the vicinity of the cross-linking temperature, , which can be, but need not be [8], within 5£¿K of the clearing temperature of the liquid crystal phase cross linked in the elastomer. The notion that cross-linking temperature, , is a relevant thermodynamic parameter is a novel concept in the field of liquid crystal elastomers. While being not obvious for LSCEs cross linked in the vicinity of the
%U http://www.hindawi.com/journals/acmp/2013/752060/