X-ray study of the ordered smectic phases in some benzylideneanilines

Abstract

From X-ray experiments, performed on both single domains and powder samples, the two ordered smectic phases (S4 and S3) exhibited by a few n-(alkoxybenzylidene)-p-n-alkylaniline compounds appear respectively as SBc (tilted) and SBA (normal) phases : the phase transition between these two phases is a first order transition. Moreover, the description of the nature of these phases must also take into account an extra feature observed on some X-ray powder patterns : the splitting of the ring corresponding to the Bragg reflection on smectic layers into two rings. To interpret this phenomenon, we assume that there occurs a segregation into domains of different layer thickness, thus implying the existence of two kinds of molecular conformations differing in length. In the last part of this report, we review the classification problems related to the smectic ordered phases using new information provided by the study of the S4 and S3 phases