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 )
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.