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Phase separation of binary mixtures in thin films: Effects of an initial concentration gradient across the film
, K. Binder, S. Puri
Published in
2012
Volume: 85
   
Issue: 4
Abstract
We study the kinetics of phase separation of a binary (A,B) mixture confined in a thin film of thickness D by numerical simulations of the corresponding Cahn-Hilliard-Cook (CHC) model. The initial state consisted of 50% A:50% B with a concentration gradient across the film, i.e., the average order parameter profile is Ψ av(z,t=0)=(2z/D-1)Ψ g, 0≤z≤D, for various choices of Ψ g and D. The equilibrium state (for time t→) consists of coexisting A-rich and B-rich domains separated by interfaces oriented perpendicular to the surfaces. However, for sufficiently large Ψ g, a (metastable) layered state is formed with a single interface parallel to the surfaces. This phenomenon is explained in terms of a competition between domain growth in the bulk and surface-directed spinodal decomposition (SDSD) that is caused by the gradient. Thus, gradients in the initial state can stabilize thin-film morphologies which are not stable in full equilibrium. This offers interesting possibilities as a method for preparing novel materials. © 2012 American Physical Society.
About the journal
JournalPhysical Review E - Statistical, Nonlinear, and Soft Matter Physics
ISSN15393755