Defect dynamics and coarsening dynamics in smectic-<i>C</i>films

Abstract

We study the dynamics of defects generated in free-standing films of liquid crystals following a thermal quench from the smectic-A phase to the smectic-C phase. The defects are type-1 disclinations, and the strain field between defect pairs is confined to 2\ensuremath{\pi} walls. We compare our observations with a phenomenological model that includes dipole coupling of the director field to an external ordering field. This model is able to account for both the observed coalescence dynamics and the observed ordering dynamics. In the absence of an ordering field, our model predicts the defect density \ensuremath{\rho} to scale with time t as \ensuremath{\rho} ln\ensuremath{\rho}\ensuremath{\propto}${\mathit{t}}^{\mathrm{\ensuremath{-}}1}$. When the dipole coupling of the director field to an external ordering field is included, both the model and experiments show the defect coarsening proceeds as \ensuremath{\rho}\ensuremath{\propto}${\mathit{e}}^{\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\alpha}}\mathit{t}}$ with the strain field confined to 2\ensuremath{\pi} walls. The external ordering field most likely arises from the director's tendency to align with edge dislocations within the liquid-crystal film.