Surface Effects on Phases Transitions in Smectic Membranes.

摘要

In liquid crystal materials, frustration between competing interactions and thermal fluctuation results in the observation of many different phases (up to 5) in a relatively narrow temperature window (usually about 30K). Identifying the interactions as well as finding out the nature of those interactions that stabilize those phases is a very important and interesting question. In this thesis, we study the interlayer interactions in smectic liquid crystal materials through the study of surface effects on the phase transition in smectic liquid crystal films.;Elevated surface interactions in liquid crystal materials result in surface transitions higher in temperature than the bulk transitions. In the free standing film geometry employed in our research, the nature of the surface order (surface transition temperature, number of surface layers, surface critical exponent, etc.) are intrinsic properties of the system.;With the surfaces ordered before the rest of the sample, the interior transitions take place under the effective field created by the ordered surfaces. By studying the effects of this surface field on the interior transitions, as well as the interactions between surface layers and interior layers, and the interactions between the surface layers, we are able to obtain valuable information about the nature of the interlayer interactions in smectic liquid crystal materials. Our results also provide new insights into the nature of the surface transitions in the ordered surface region of the phase diagram.