High resolution X-ray measurements on smectic C* liquid crystal mixtures

We report on high resolution x-ray measurements of two commercial ferroelectric liquid crystal mixtures. Both materials show a second order smectic A to smectic C phase transition. The measured tilt angle, (pp was fitted to the power law expression Φp = ΦOt-β(with the reduced temperature, t = (Tc - T)/Tc; Tc is the smectic A to smectic C phase transition temperature), giving β = 0.31 • 0.02 for one and β = 0.33 ± 0.03 for the other mixture. We discuss the discrepancy between the x-ray tilt angles and those obtained by conventional optical methods.