Transition between curved and angular textures in binary fluid convection.

We report a transition from a curved texture to an angular texture in Rayleigh-B enard convection in a mixture of ethanol and water. The transition occurs as the Rayleigh number is reduced from a high value and approaches the traveling-wave branch and is observed at negative values of the separation ratio in uid mixtures, but not in a pure uid. We show that this transition may be understood in terms of a generalization of the Swift-Hohenberg free energy functional. A large increase in wavenumber rigidity is observed as the traveling-wave transition is approached. PACS numbers: 47.54+r, 47.20.Lz, 47.27Te