Preferred equilibrium structures of a smectic-A phase grown from an isotropic phase: Origin of focal conic domains

Preferred equilibrium structures of a smectic-A phase grown from an isotropic phase have been investigated theoretically and experimentally. The surface-integral equation reported in our recent paper [H. Naito, M. Okuda, and Z. Ou-Yang, Phys. Rev. Lett. 70, 2912 (1993)] and a surface-differential equation are derived from the Euler-Lagrange equations for the variation of the nucleation energy of the smectic-A phase. Toroidal structures of the smectic-A phase are shown to be solutions of both equations and are observed experimentally in binary mixtures of octyloxycyanobiphenyl with dodecyl alcohol. It is also shown that focal conic domains are developed from such structures.