SURFACE MOLECULAR ANCHORING IN MICROCONFINED LIQUID-CRYSTALS NEAR THENEMATIC SMECTIC-A TRANSITION

The effect of the diverging bend elastic constant, K33, on the nematic director field of 4'-octyl-cyanobiphenyl (8CB) in submicrometer cylin drical cavities in a polycarbonate matrix, as the nematic-smetic-A pha se transition is approached, is investigated with deuteron nuclear mag netic resonance (H-2-NMR). The H-2-NMR spectra and the use of Frank el astic theory enable us to monitor the actual surface anchoring angle p rofile, determine the density of point defects in the escaped structur e, and estimate the anchoring strength to be W(theta)=7X10(-4) J/m2, w hich is temperature independent. The large value of W(theta) and the l ack of evidence for pretransitional smectic layering in our NMR spectr a show that although the orientational anchoring is strong, the polyca rbonate surface is too rough to induce substantial surface smectic ord er in the nematic phase. The saddle-splay elastic constant K24 for 8CB is estimated to be larger than the elastic constant K11.