Imprinting of nematic order at polymer network surfaces as a function of cross-link density

The effect of polymer structure on imprinting of nematic order on the surface of cross-linked polymer networks was studied. Polymer surfaces were formed in contact with a nematic phase by polymerization-induced phase separation in a nematic solvent. Nematic order imprints upon the interface, giving an easy axis for nematic anchoring. Surface imprinting diminished with decreasing cross-link density of the polymer network. This trend coincides with an increase in monomeric motion, as shown by a simple argument. This is an example of crossover from solidlike to liquidlike behavior in a cross-linked polymer as the cross-link density is varied. Also, surface imprinting is important because it can affect electro-optical properties of dispersions of polymers and liquid crystals made by polymerization-induced phase separation. [S1063-651X(99)07901-5].