Focal conic domains with positive Gaussian curvature and saddle-splay rigidity of smecticLαphases

Abstract

We report on the experimental observation of a different type of focal conic domain with positive Gaussian curvature. A particular type of these domains is usually given the name ‘‘spherulites.’’ Their appearance is due to a low (probably negative) value of the saddle-splay elastic constant. These domains are observed in the lamellar ${\mathit{L}}_{\mathrm{\alpha }}$ phase with a low cosurfactant to surfactant (c/s) ratio. The increase of this ratio results in usual focal domains with negative Gaussian curvature. It allows us to conclude that the saddle-splay constant is governed by the c/s ratio, and changes sign from positive to negative when c/s decreases.