Comparative x-ray measurements of a de Vries smectic- material in bulk and confined geometries

X-ray investigations have been carried out on a material exhibiting the de Vries smectic-A (Sm-A) phase in bulk and confined geometries. In the confined geometry realized by confining the material in an Anopore membrane, while the minimal layer shrinkage feature characteristic of the de Vries materials is retained, the overall change of the layer spacing from the Sm-A to the Sm-C phase is much less compared to the bulk geometry and also the transition gets smeared out. A "crossover" behavior, which has been recently ascribed to different molecular packing arrangements within the Sm-A phase, is seen in both geometries. With the support from data on another non-de Vries type of material we suggest that the associated feature may not be due to a phase transition, but competition between the thermally driven stretching and molecular tilt.