Multi-electron bubbles, virus heads, carbon Buckeyballs, and soccer balls are examples of objects arranged in an ordered lattice on a spherical surface (or nearly spherical). The equilibrium state of such spherical crystals is an old problem, dating back to J. J. Thomson. While a crystal on a flat surface tends to avoid disclinations and dislocations, a spherical crystal must have disclinations. According to recent predictions, excess dislocations will form on large spheres. Morover, these dislocation lines terminate in the lattice, which is never observed on flat surfaces [Bowick, Nelson and Travesset]. Looking at colloidal particles on droplets, we have observed equilibrium configurations that are in excellent agreement with the earlier predictions[article].
(w/ Michael Nikolaides and Andreas Bausch, T. U. Munich; A. Cacciuto and Mark Bowick, Syracuse U.; Alex Travesset, UIUC; Ming Hsu, D. R. Nelson and D. A. Weitz, Harvard.)


Electrostatic and capillary forces at liquid interfaces

Colloidal particles adsorbed at an oil-water interface exhibit a surprising long-range attraction in addition to the expected electrostatic repulsion. We propose that the charges on the colloidal particles create electric fields that induce polarization charges at the interface (owing to the different dielectric constants of the two fluids). The field pushes on the polarization charges and distorts the interface, which leads to a long-range capillary attraction [article]. We can measure these forces directly using video microscopy and (sometimes) laser tweezers.

(w/ Versa Clark and Ryan McGorty, UMass physics; Michael Nikolaides and Andreas Bausch, T. U. Munich; Cyprien Gay, CRPP-CNRS, France; Ming Hsu, Michael Brenner and David Weitz, Harvard)