Investigation of Antiferroelectric Liquid Crystalline Free-Standing Films by Transmission Ellipsometry

Abstract

Thin free-standing films (FSFs) of an antiferroelectric liquid crystal (AFLC) were investigated by transmission ellipsometry. The phase difference between p-polarized and s-polarized light was measured as a function of the temperature and the incidence angle of the light beam. It was found that the structure of an FSF with two layers is anticlinic (SmC* A) throughout the temperature range investigated whereas the bulk sample shows several phases, from SmC* A to SmA phases. The four layer FSF showed only one phase transition (from SmC* A to SmA) in this temperature range. Even for such a thin film as one with five layers, a subphase or subphases between SmC* A and SmA were found.

Ordering of Chiral Smectics in Freely Suspended Film

“…A freely suspended film of chiral smectics is a very interesting and useful system to elucidate not only the film ordering itself but the property of a bulk phase [1][2][3][4][5][6][7][8][9][10]. By a study of such system, the phase structure free from an anchoring effect because of boundary walls can be observed [9,10].…”

“…By a study of such system, the phase structure free from an anchoring effect because of boundary walls can be observed [9,10]. On the other hand, surface layers of the film are known to order at a temperature higher than the bulk critical temperature for both ferroelectric [1][2][3][4][5] and antiferroelectric [6,7] smectics. Now, a ferroelectric material 4-(3-methyl-2-chloropentanoyloxy)-4 0 -heptyloxy-biphenyl (C7) shows a first-order phase transition from a smectic A phase (SmA) to a smectic C phase (SmC Ã ) [11], whereas most of ferroelectric smectics exhibit a second-order phase transition.…”

Investigation of Refractive Indices of Free-Standing Films by Ellipsometry

“…We simulated the phase difference D between the p-polarized and s-polarized light outgoing from the FSFs of MHPOBC [1], so as to investigate the layer structure of FSFs in smectic phase, where refractive indices were assumed to be the same as those of the bulk sample (n e ¼ 1.64, n o ¼ 1.50 [5]). Because the FSFs is composed of a tremendous numbers of molecules in each layer of FSFs, therefore the physical concept of refractive index may hold even in such thin films.…”

Surfaces and Interfaces of Free-Standing Smectic Films

“…For example, ellipsometry (e.g. [36,64,66,67,[77][78][79][80]) and X-ray investigations [17, 19-21, 27, 45, 54, 61, 62, 71, 80-86] have been successfully applied.…”

“…Directly related to the structure of the films is their ferroelectric, antiferroelectric and ferrielectric behavior [23,36,66,[77][78][79][80][87][88][89][90][91][92][93][94]. In films of a few molecular layers, these properties can change dramatically with respect to the bulk samples.…”