Geometric control of topological defects in nematic liquid crystals via micropillar spacing.

Topological defects in liquid crystals (LCs) emerge from elastic distortions of the director field under confinement, but the influence of geometric confinement in open microstructured systems remains poorly understood. Here, we both experimentally and computationally investigate how pillar spacing and spatial distribution govern defect formation in nematic LCs confined within micropillar arrays. By varying the lattice spacing from 10 to 60 µm and modulating interstitial space, we decouple local anchoring effects from global geometric constraints. We identify distinct regimes of defect behavior. Specifically, strong confinement suppresses isolated point defects and favors disclination lines, whereas weak confinement yields independent pillar-bound -1 defects. At intermediate spacings, defects delocalize from pillars and stabilize within interstitial regions, leading to the formation of both +1 and -1 defects. These states are not present in uniformly distributed arrays with identical spacing, highlighting the importance of free volume connectivity. These findings establish geometric confinement as a key parameter for programming topological states in LCs.