78th Annual Meeting of the APS Division of Fluid Dynamics (Nov 23 — 25, 2025)

P014: Interfacial Intricacies: Phase Transitions in Liquid Crystals

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At a critical temperature, liquid crystals transition from a randomly oriented isotropic phase to a uniformly aligned nematic phase. When a thin layer of liquid crystalline solution sandwiched between two glass plates is cooled, the phase transition begins with the nucleation of nematic drop-like tactoids. Viewed between crossed polarizers, the orientationally-ordered structures produce the vibrant colors of the tactoids. As temperature decreases and tactoids further grow, they coalesce and form networks of nematic liquid crystal. The dark isotropic areas are distinguished as negative tactoids. In both the positive nematic and the negative isotropic tactoids, the nematic-isotropic phase boundaries require tangential alignment of the liquid crystal. To satisfy this constraint, the tactoids maintain a topology in which the director rotates by 2π around the boundary.In this experiment, the temperature across the image is non-uniform, capturing both the early-stage formation of positive tactoids and the late-stage coalescence leading to negative tactoids. The intricacies of liquid crystal surface energies, specifically the anchoring conditions at interfaces and their effect on the bulk free energy density, hold many secrets for further investigation.