CONVECTIVE PATTERNS IN A BINARY MIXTURE WITH A POSITIVE SEPARATION RATIO

We pesent an experimental study of the convective patterns and their dynamics occurring in a binary mixture presenting a positive separation ratio. In this situation, both the concentration and the temperature fields are destabilizing, and they lead to two different kinds of convective patterns. Using quantitative optical methods, we have measured the convective motion wavevectors and their non-linear amplitude. For small temperature differences, only the concentration field is destabilizing and the convective motions are organized in a square pattern. We study the evolution of the wavevector and the amplitude of the square pattern. For larger temperature differences both fields are destabilizing and we investigate the competition between the square pattern, reminiscent of the concentration field, and the roll pattern associated with the temperature field. By studying the dynamics of this competition we have evidenced the existence of traveling waves which have been recently predicted by Linz et al.