Organization of droplets at an air-LC interface

Liquid Crystals are extraordinary materials for the organization of fluids and nanoparticles. The director field wraps around colloidal inclusions and inevitably forms topological defects to meet far-field boundary conditions. Droplets of isotropic fluids which promote planar anchoring form boojums in the surrounding LC which cause bulk quadrupolar distortions. At an air-LC interface the droplets directly contact the air and one boojum can disappear leaving a solitary boojum pointing down. As the liquid crystal layer becomes thinner, the hybrid anchoring of the LC layer causes the boojum to tilt enabling the formation of dipolar chains. As the layer becomes thinner still, the bottom planar alignment forces the second boojum to reappear recovering the quadrupolar alignment. The elastocapillary force associated with droplets at an air-LC interface is a surprising many body force which can distort the layer thickness by up to 1 micron leading to the formation of rounded superstructures containing thousands of droplets. Polydisperse droplets can enable the formation of branched structures where a mix of dipolar and quadrupolar interaction allows for the formation of y-branches. The self-assembly properties of LC enable the formation of interesting emulsions and switchable hybrid materials.