An X-Ray Study of a Smectic C and Smectic A Liquid Crystal Polyacrylate

An X-ray study was performed on powder specimens and on stretched oriented fibres of a smectic polyacrylate. The X-ray diffraction patterns showed the existence of monolayer smectic A. and bilayer smectic C mesophases that coexisted over a well defined range of temperature. In the latter mesophase the mesogenic groups were tilted with respect to the smectic layer normal by an angle beta approximate to 30 degrees. The electron density profile rho(z) along the direction normal to the smectic layers in the smectic C mesophase was determined by Fourier inversion and indicated the presence of a minor interdigitation of the terminal substituents. The phase problem related to the Fourier inversion was solved by using a pattern recognition approach based on the histogram of the electron density map. The positional smectic layer order parameters were also calculated for the first five harmonics of the positional distribution function of the smectic layers and their values suggested a well ordered layer structure