Microscopic particles and droplets tend to arrange themselves into regular patterns when suspended in a nematic liquid crystalline matrix. Using numerical simulations, we are investigating the interaction between such particles and the anisotropic matrix, especially through the nucleation of orientational defects. Dynamic simulations have shown the formation of lines resembling experimental observations (see graphics below). Our ongoing work focuses on achieving multi-dimensional patterns, and the possibility of using the self-assembly as a method for making photonic crystals with tunable bandgaps.

(2D self-assembly of micro-droplets with homeotropic surface anchoring in a nematic liquid crystal. The greyscale contours indicate the director orientation. Click here for more details.)

In addition, we have studied how the macroscopic flow field affects the defect configuration in return. In dynamic simulations of drop motion in a Leslie-Ericksen nematic, we predicted that on a translating drop, a Saturn ring defect will be "convected" downstream. If the drop velocity is sufficiently high, the ring will be ejected from the drop into the wake and turn into a hedgehog point defect. This has since been confirmed by experimental observations. The images below illustrates the transformation process.

(A time sequence of snapshots showing the transformation of a Saturn ring (a) into a point defect (f) on a silicone droplet (diameter ~ 50 µm) rising in 5CB. The rising speed is on the order of 1 µm/s and the sequence spans roughly 3 hours. Click here for more details.)