Divergence of the Bend Curvature Coefficient above the Nematic-Smectic a Phase Transition; Freedericksz Transition.

A magnetic induced bend deformation (the Freedericksz transition) was used to the bend curvature coefficient as a function of temperature above a second order nematic-smectic A (NA) phase transition in liquid crystal 4-n-pentylphenylthiol-4'-n-octyloxybenzoate (8S5). It was found that the bend curvature coefficient diverged with an exponent of .67 plus or minus .02. From a light scattering measurement of the twist mode the NA transition temperature was determined. It was found that the NA transition temperature determined from light scattering agreed, within error bars, with the Freedericksz result. The need for correction to scaling terms in the Freedericksz fitting equations is discussed. A magnetic field induced shift in the NA transition temperature was also observed and was found to be sample thickness dependent.