Nematic caps on colloidal particles in a nematogenic liquid under an electric field.

We examine the localized nematic regions (caps) on spherical colloidal particles suspended in a nematogenic liquid in the isotropic phase in the bulk by solving the Poisson equation with an orientation-dependent dielectric tensor. These caps appear and grow with an increasing applied electric field. We assume positive dielectric anisotropy of the nematogenic liquid and a high dielectric constant of the particles. Then, the electric field becomes the strongest near the poles of each particle along the field direction, leading to nematic caps. This cap formation occurs continuously for homeotropic anchoring, but is a discontinuous transition otherwise. We also discuss how the nematic caps can be observed in dielectric response, birefringence, and depolarized light scattering.