Coalescence of Sessile Radial Nematic Droplets

We report on experiments that demonstrate coalescence of two “largely” radial nematic liquid crystal (NLC) droplets with homeotropic anchoring. Previously, extensive theoretical work has suggested that coalescence of two NLC radial droplets is prevented by the energy barrier for formation of a topological defect between the two droplets [1, 2]. Our experimental work suggests that droplet wetting and deformation lowers this energy barrier. We describe the spontaneous formation of a Q = −1 defect at the neck between two sessile droplets, and the subsequent annihilation of defects to generate a single radial hedgehog droplet with a Q = +1 defect. Using polarized optical microscopy (side and top views), we are able to observe droplet merging and defect and director evolution, as well as characterize how the drop contact angle influences likelihood of coalescence. Simulations were also employed to build connections with the POM images and director configurations, as well as to calculate the change in energy due to distortion of the director field, which suggests that the coalescence energy barrier is lowered.

[1] Heppenstall‐Butler , M. , Williamson , A. M. and Terentjev , E. M. 2005 . Liq. Cryst. , 32 : 77

[2] Terentjev , EM . 1995 . Europhys. Lett. , 32 : 607