Aggregation and orientation phenomena in constrained films of LC poly(olefin sulfone)s

The studied liquid crystalline poly(olefin sulfone)s are characterized by polar, helical backbones and rod-like cyanobiphenyl side groups. Starting from isotropic spin-coated films annealing results in spontaneous self-assembly forming well-aligned, homeotropic films. The spontaneous orientation process leads to a significant decrease of the pi-pi* absorbance of the side groups and results in a vertical degree of order up to 0.8. Moreover, X-ray reflection studies indicate that the orientation process is accompanied by the formation of layered structures within the film parallel to the interfaces. Hypsochromic shifts of absorption and bathochromic shifts of fluorescence indicate strong pi-pi* interactions of the aromatic side groups in the ground state caused by the self-association forming H-aggregates. The structure-property relationship suggests, that orientation and aggregation are driven by the liquid crystallinity and the segregation tendency of the polymers in the constrained films. (C) 1998 Elsevier Science S.A. All rights reserved.