A New Method for High Accuracy Tilt Angle Measurements in Ferroelectric Liquid Crystals

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Abstract
A new method for measuring the tilt angle between the long molecular axes and the normal to the layer planes in ferroelectric liquid crystals is described. This technique provides a direct and continuous determination of the tilt angle as a function of temperature in contrast to existing techniques. Therefore, it is specially well-suited to studies of phase transition phenomena. The method is applied to the particular case of the smectic A(SmA) to chiral smectic C(SmC*) phase transition in p-(n-decylox-ybenzylidene)-p-amino-(2-methyl-butyl) cinnamate (DOBAMBC). The tilt was found to exhibit a behaviour that can only be explained within a mean-field model if new terms are included in the free-energy expansion, as has been recently proposed.