Kinetics of layer-thinning transitions in overheated smectic films

The kinetic behavior of dislocation loops in overheated free-standing smect ic-A films is reported. The loops open at velocities that are much faster t han those seen in nonoverheated films. The velocities increase dramatically as a function of temperature and vary slightly as a function of film thick ness. The behavior of dislocation loops induced with a pulsed resistive wir e heater is identical to that of the loops giving rise to the layer thinnin g transition. In addition, the interaction between two simultaneously nucle ated dislocation loops is analyzed. The observed interactions give evidence that thinning occurs in the interior of the film. The results support a mo del for the layer-by-layer thinning transition based on the nucleation of d islocation loops.