Influence of Surface on the Development and Dynamics of Droplet Coalescence in Optical Cells at the Isotropic Liquid–Liquid Crystal Phase Transition

The work presents results of studies of coalescence of nematic liquid crystal droplets surrounded by isotropic liquid. With the aid of high-resolution optical microscopy and high-speed video recording coalescence of droplets in thin optical cells has been studied. Cells with planar and homeotropic boundary conditions for the liquid crystal director were used. It is shown that depending on boundary conditions at the cell surface the coalescence process at the initial stage develops in a different manner. In a cell with planar boundary conditions at the initial stage we observe linear dependence of the width of the neck between droplets on time. At subsequent stages the influence of surface leads to slower dynamics. The final stage of coalescence is characterized by exponential relaxation of the droplet to the equilibrium shape. At coalescence of droplets whose diameter exceeds the cell thickness, we observed an intermediate stage with power-law dependence of the neck width on time. The duration of this stage increases with increasing the droplet size. Capillary velocity and characteristic times at different stages of coalescence were determined. Characteristic times for the initial stage increase linearly with increasing the droplet size. For the middle stage the characteristic times increase proportionally to the third power of the droplet radius.