Interfacial tension at the boundary between nematic and isotropic phases of a hard rod solution

The excess surface free energy per unit area or interfacial tension is dete rmined for hard-rod isotropic and nematic phases coexisting at equilibrium. The number density and order parameter profiles across the interface are o btained by minimizing the free energy in the inhomogeneous fluid using an a pproach that generalizes Onsager's classical theory to spatially inhomogene ous hard rod solutions. The excess surface free energy is a minimum when th e director in the bulk of the nematic phase is at a 90 degrees angle to the surface normal, indicating that this tangent alignment is the preferred or ientation likely to be-observed in practice. The surface tension for a tang ent director is found to be 0.316k(B)T/(dL), where hg is Boltzmann's consta nt, T the absolute temperature and d and L are the diameter and length of t he rods. The dependence of the rod concentration on position across the int erface is nonmonotonic.