Structural evolution of a hedgehog defect across the N–SmA phase transition in freely suspended film

Although the nematic – smectic transition is now well understood, the precise transformation of an hedgehog defect upon entering the smectic A phase remains largely unexplored. Here, we investigate the evolution of a hedgehog defect core in a freely suspended liquid crystal film during nematic – to – smectic-A (N – SmA) phase transition. As the temperature decreased, we first observed the emergence of a radially striped configuration, followed by the formation of focal conic domains (FCDs). All the FCDs tend to disappear except for one that remains slightly longer, corresponding to the precise location of the hedgehog defect had been located. We present two different models (dynamic evolution by waving or winding) that explain the various steps involved in the transient states in detail: the formation of the striped configuration and the subsequent assembly of FCDs.