Physics Colloquium - Monday, February 19th, 2007, 4:00 P.M.

E300 Math/Science Center; Refreshments at 3:30 P.M. in Room E200

Alberto Fernandez-Nieves
Harvard University

Nematic order in spherical shells

We use double emulsion drops to experimentally realize a system to investigate the defect structure in spherical shells of nematic liquid crystal. The ground state of this system is predicted to exhibit a tetrahedral arrangement of four surface defects in a structure reminiscent of a baseball. Instead, we find a much richer set of coexisting defect structures dictated by the inevitable thickness of even the thinnest shells, and the resultant variation of the shell thickness around the sphere. These structures are characterized by a varying number of disclination lines and pairs of surface point defects, one each on the inner and outer surfaces of the nematic shell. The inevitable thickness variation of the shell determines the separation of the defects, and the ultimate configuration. In the limit of thick shells, the structure ultimately merges with that of a bulk nematic liquid crystal drop.