Raman Spectroscopic and Calorimetric Investigation of the Multiple Smectic Phase Material TBBA

Abstract

Smectic mesophase formation and structure have been the subject of vigorous scientific inquiry in recent years. ^1–6 Among those phases investigated most intensively, the B and H phases are thought to possess the highest degree of local three-dimensional order. As determined by X-ray crystallography ^1–5 both phases exhibit long-range two dimensional pseudo-hexagonal order within each layer; in addition there appears to be some degree of correlation between planes.^1,5 In the H phase the director lies at an angle to the smectic planes, while in the B phase it is normal to the planes. The nature of the degrees of freedom available and the intermolecular ordering in these phases has been the subject of a number of theoretical and experimental studies.^3,7,8 Since terephthal-bis-butylaniline (TBBA) exhibits a smectic H phase as well as at least eight other phases (see schematic below), it has been extensively studied by various experimental techniques including X-ray,⁴ NMR,⁹ DSC,¹⁰ neutron scattering,¹¹ infrared¹² and Raman^10,13–14 spectroscopy. This paper provides new information on the nature of the various smectic phases observed in TBBA.