No abstract

No abstract

It has been discovered that the products of degradation of heated paper evaporated on glass constitute a low anchoring energy substrate for the nematic phase of MBBA (methoxy benzylidene butylaniline). The extrapolation length b = K/2Ws is of the order of 100 J.Hn. In very thin specimens the anchoring is conical at low temperatures and becomes homeotropic at higher temperatures. A transition 10 (ordinary) strong anchoring conditions appears at still higher temperatures. presumably due to the appearance of a slight isotropic layer of MBBA at the interface. We have been interested in the study of defects typical of the weak anchoring phases. in specimens thinner than b. One observes the existence of Bloch walls. This typical defect allows for a direct measurement of the surface anchoring energy (W s -10·-4 erg/m'). Other defects are nuclei of strength ± 1 (in repulsive or attractive interaction with the walls according to whether they are + 1 or -I nuclei). and reversing points which separate Bloch wall segments of opposite torsions.We demonstrate that Bloch walls constitute. in thin specimens (h