Liquid crystalline elastomers based on diglycidyl terminated rigid monomers and aliphatic acids. Part 2. Mechanical characterization

In this paper the orientational behaviour and the mechanical properties of four LC elastomers, obtained by reacting two mesogenic epoxy monomers, DOMS and PHBHQ, with two aliphatic acids having four (AA) and eight (SA) methylene groups, respectively, have been studied. Stress-relaxation experiments performed at a strain value epsilon=0.2 showed shorter relaxation times and lower relaxation moduli for AA-based elastomers as compared with the PHBHQ-SA system. Stress-strain curves of the LC elastomers showed the plateau attributed to the soft elasticity. The lower crosslink density in the case of DOMS-based elastomers affected the tensile properties adversely. Moreover, PHBHQ-SA was found to show poor strain recovery and it recovered the original size only upon heating to isotropic phase. This evidence was also confirmed by isostrain measurements. Dynamic mechanical thermal analysis (DMTA) confirmed the existence of a heterogeneous, more branched structure in the case of DOMS-based systems. The particular features of the DMTA response strongly depend on the material composition and, in general, were found in agreement with other evidences from the literature. (c) 2005 Elsevier Ltd. All rights reserved.