The Dependence of Volumetric Properties on the Molecular Composition of Nematic Liquid Crystals

Abstract

Abstract Density studies on various terminally polar and non-polar nematic liquid crystals, measured as a function of temperature, are reported. The molar volumes were fitted to model equations by a non-linear numerical least squares fit. These equations contain non-linear terms of the form c I (T - T I c)βI for T > T I c and - C N (.T N c - T)βN for T < T N c. It is shown that the coefficients C N and cI are correlated with the extrapolated volume discontinuity ΔV c,99 at the nematic-isotropic phase transition temperature T c. Furthermore, for all liquid crystals investigated there exists a correlation between ΔV c.99 and the order parameter S zz (t r = 0.99) as determined by infrared dichroism. Our density measurements suggest that C N and C I depend on the molecular structure of the liquid crystal and are not universal for the nematic-isotropic phase transition. Assuming universal exponents βN and β1, we evaluate the average values βN = 0.388 + − 0.096 0.085 and βI = 0.135+ − 0.065 0.045.