SHAPE MEASUREMENTS OF FACETED SMECTIC-A DROPLETS

We have measured profiles of smectic A droplets in air as a function of temperature. As the droplet is cooled below the nematic-smectic A transition temperature T(NA), the facet radius is proportonal to (T(NA) - T)-alpha, with alpha = 0.45 +/- 0.1, an exponent consistent with that measured for the layer compression modulus B. While the relaxation time for shape changes upon cooling is less than one minute, that for heating ranges from hours to days, depending on (T(NA) - T). An estimate of the energy barrier to nucleating new layers suggests that that process is forbidden and that another explanation of the relaxation-rate asymmetry must be found.