Surface-Induced Helix-Unwinding Process in Thin Homogeneous Ferroelectric Smectic Cells of DOBAMBC

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Abstract
Under conditions where molecules are forced parallel to the cell surfaces but do not orient themselves along a particular direction, we have observed the unwinding process. The cell thickness dependence of the transition temperature from Sm A to distorted Sm C* or Sm C, T c(d), has been obtained. The apparent tilt angle, θ', has also been obtained as a function of d and T-T c(d) from two directions giving the darkest view between crossed Nicols. For the 1.6 µm cell, θ' is almost equal to the true tilt angle, θ, at low temperatures but shows a jump from 0° to 9° at T c. We have qualitatively explained these results in terms of the distortion in the azimuthal angle ϕ of the director, pointing out the importance of its spatial and temporal fluctuations.