TRANSITION BETWEEN CURVED AND ANGULAR TEXTURES IN BINARY-FLUID CONVECTION

We report a transition from a curved texture to an angular texture in Rayleigh-Benard convection in a mixture of ethanol and water. The tran sition occurs as the Rayleigh number is reduced from a high value and approaches the traveling-wave branch and is observed at negative value s of the separation ratio in fluid mixtures, but not in a pure fluid. We show that this transition may be understood in terms of a generaliz ation of the Swift-Hohenberg free energy functional. A large increase in wave-number rigidity is observed as the traveling-wave transition i s approached.