Unusual slow fluctuations as revealed recently by dynamic light scattering close to the $\mathrm{Sm}-A–\mathrm{Sm}{-C}_{\alpha }^{*}$ phase transition in the antiferroelectric liquid crystal 4-(1-methylheptyloxy-carbonyl)phenyl $4^{\prime }$-octyloxy biphenyl-4-carboxylate can be explained by the electrostatic coupling between impurity ions and director fluctuations. Within the vicinity of $\mathrm{Sm}-A–\mathrm{Sm}{-C}_{\alpha }^{*}$ transition, the relaxation rate of the slow mode depends linearly on temperature, but with a different slope in each phase. The square root of its intensity shows a clear Curie-Weiss divergence at the phase transition, which is a direct confirmation of the electrostatic coupling mechanism.

• Received 12 October 1998

DOI:https://doi.org/10.1103/PhysRevE.60.6788