Molecular orientation in quenched channel flow of a flow aligning main chain thermotropic liquid crystalline polymer

We report measurements of molecular orientation in solid specimens of a mai n-chain thermotropic liquid crystalline polymer (LCP) that were quenched fr om mixed shear-extensional channel flows. The polymer under investigation i s a random copolyether with mesogens separated by flexible hydrocarbon spac ers. This polymer is known to exhibit 'flow aligning' dynamics under slow s hear flow. Experiments were designed to preserve the molecular orientation state, representative of steady, isothermal channel flow in the solid sampl es, so that comparisons could be made against in situ channel flow measurem ents on other main chain thermotropes without flexible spacers, including a commercial fully aromatic copolyster. In the flow aligning material, littl e change in orientation was found in slit-contraction flows, and only modes t drops in orientation were found in slit-expansion flow. This contrasts st rongly with data on commercial LCPs, suggesting that these materials may be of the 'tumbling' type. (C) 2001 Published by Elsevier Science Ltd.