Nanoparticle assembly in smectic-A to nematic phase transition at undulated surfaces*

Topological defects in liquid crystals are effective templates for nanoparticle (NP) assembly. In a hybrid-aligned smectic-A (SmA) liquid crystal, NPs assemble at the cusp defects of focal conic domains (FCDs). Adding two-dimensional undulations to one of the confining surfaces stabilizes defects in the nematic phase, as well, suggesting routes to patterned and switchable NP assembly at the SmA-nematic phase transition. We model how NPs assemble in the SmA-to-nematic phase when one of the hybrid-aligned surfaces has 2D undulations, using a multi-step Landau-de Gennes free energy minimization scheme accounting for smectic FCD configurations and elasticity. We show that the NPs assemble sequentially at defects and confining surfaces, with the assembly sequence dependent on NP surface anchoring. We explore how the curvature of the undulated surface influences to this sequential assembly. We also examine how the presence of NP assemblies affects, in turn, the defect structures that arise in the SmA-nematic phase transition.