Pattern Formation And Selection In Phase Separation Coupled With Chemical Reaction

The phase separation of polymer blends and/or block copolymers is one of the important topics in polymer condensed matter physics. The phase separation of polymer blends usually proceeds under the presence of external fields such as shear flow, temperature gradient, or chemical reaction. On one hand, the study of phase separation of polymer blends accompanied by chemical reaction is very important from theoretical point of view. It not only can provide theoretical guidance to the pattern formation and selection in polymer blends under symmetry-broken field, but also has far-reaching implication in pattern formation and selection in biological systems due to the fact that there also exists phase separation between water and fat in addition to the complicated biochemical reactions in biological systems. On the other hand, such study is also important from industrial perspective, and it can offer technological guidance to such industrial processes as reactive blending and reaction injection molding.In this thesis, the Time-Dependent-Ginzburg-Landau approach is employed to simulate the phase separation dynamics of polymer blends coupled with chemical reaction. The main content and results are as follows:1) The phase separation dynamics of a ternary mixture (A, B and C) coupled with a reversible isomerization reaction between the two constituents A and B is investigated. The analytical study of model equations demonstrates that the free energy functional form of TDGL equation describing the present system is similar to that of the mixture composed of a diblock copolymer and a homopolymer. Our simulation study reveals that in the case of equal forward and backward reactionrates, the lamellar thickness scales with the reaction rate constant as a single power law, , regardless of the high or low reaction rate regimes. Thepresent study sheds insight to the unique features of the involvement of chemical reaction in the phase separation of the ternary mixture. If chemical reaction and phase separation take place simultaneously, the different pattern evolutions at high and low reaction rate constants originates from the competition between domain coarsening due to phase separation and the breakup of the continuous phase due to chemical conversion. The different pattern evolutions at high and low reaction rate constants when chemical reaction lags behind phase separation can be interpreted in terms of the discrepancy between the domain sizes at the time immediately before the turning on of the chemical reaction and the inherent lamellar thickness determined by the reaction rate constant. It is also pointed out that the crossover of the ternary mixture from one phase region to another, due to the concentration change between A and B, might be able to generate interesting steady-state domain patterns.2) The phase separation dynamics of a ternary mixture (A, B and C) coupled with an interfacial chemical reaction A + B C in two dimensions is studied by computer simulation. The effect of reduction of interfacial free energy due to the presence of species C along the interface is taken into account in the study. In the case of fixed domain size, it is shown in simulation that for both reversible and irreversible reactions, the generation of species C along the interface is not affected by the reaction rate constants, suggesting that it is a diffusion-controlled process. In the case of coupling between domain growth and reversible reaction kinetics, it is demonstrated that the domain growth is frozen eventually by reaction regardless of the magnitude of the reaction rate constants. The higher the reaction rate constant is, the slower the evolution to ready state is, the larger the steady state domain size is, and the smaller the average concentration of species C is.3) The phase separation dynamics and reaction kinetics of binary mixture coupled with autocatalytic reactions (A + B 2B,A + 2B 3B) under the influence of hydrodynamic effect is investigated. In the equation of continuity of Model H, the...