Reaction-controlled morphology of phase-separating mixtures.

Abstract

The role of externally-controlled chemical reactions in the selection of patterns in phase-separating mixtures is presented. Linearized theory and computer simulation show that the initial long-wavelength instability characteristic of spinodal decomposition is suppressed by chemical reactions, which restrict domain growth to intermediate length scales even in the late stages of phase separation. Our findings suggest that such reactions may provide a novel way to stabilize and tune the steady-state morphology of phase-separating materials. Pattern formation in reaction-diffusion systems occurs throughout nature. It is well known, for example, that spiral waves and other interesting steady-state patterns can be generated by simple chemical reactions [1]. In contrast, transient patterns are formed during phase separation by spinodal decomposition in both small molecule and polymer mixtures [2,3]. These patterns, whose characteristic length scale depends on the specificity of the components of the mixture, coarsen and disappear when macroscopic phase separation is achieved at asymptotically long times. It would be desirable to devise a mechanism by which these phase-separating morphologies could be stabilized. In this Letter, we argue that chemical reactions can be used to stabilize and tune the characteristic length scale of patterns arising in phase-separating materials. Unlike the usual scenario of spinodal decomposition, where concentration fluctuations of all length scales larger than a certain critical length scale spontaneously grow with time, we show that chemical reactions introduce two cutoff lengths, thereby