Seminars

How surface ordering affects phase transitions in liquid crystal films

by Dr. Boris I. Ostrovskii (FSRC, Moscow)

Monday, December 3, 2018 from to (Europe/Berlin)
at DESY Photon Science ( Building 25 f Room 456 )
Description
We provide an overview of the influence of the surface ordering and finite size on the phase transitions in liquid crystal (LC) films. The results from the synchrotron studies of free-standing smectic films (FSSF) carried out in recent years are presented. The FSSF are particularly suitable to investigate the above problems: such films are substrate-free; the alignment of the smectic layers is almost perfect, allowing the study of single-domain samples of various thicknesses. Several phase transitions in FSSF involving smectic A (Sm-A), smectic C (Sm-C) and hexatic B (Hex-B) phases are discussed. These phases can be considered as a stack of parallel molecular layers, in which elongated molecules are oriented on average along the layer normals (Sm-A, Hex-B) or tilted with respect to them (Sm-C). The Hex-B is a three-dimensional (3D) analog of the common hexatic phase predicted by Halperin and Nelson; it exhibits long-range bond-orientational  order and short-range positional order within each layer.