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

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.