Layered structure formation in the reaction-induced phase separation of epoxy/polysulfone blends

We investigate the structural evolution of an A/B/C ternary mixture in which the A and B components can undergo a reversible chemical reaction to form C. We developed a lattice Boltzmann model for this ternary mixture that allows us to capture both the reaction kinetics and the hydrodynamic interactions within the system. We use this model to study a specific reactive mixture in which C acts as a surfactant, i.e., the formation of C at the A/B interface decreases the interfacial tension between the A and B domains. We found that the dynamics of the system is different for fluids in the diffusive and viscous regimes. In the diffusive regime, the formation of a layer of C at the interface leads to a freezing of the structural evolution in the fluid; the values of the reaction rate constants determine the characteristic domain size in the system. In the viscous regime, where hydrodynamic interactions are important, interfacial reactions cause a slowing down of the domain growth, but do not arrest the evolution of the mixture. The results provide guidelines for controlling the morphology of this complex ternary fluid.

Effect of hydrodynamic interactions on the evolution of chemically reactive ternary mixtures

Verification of numerical simulation of the self-assembly of polymer-polymer- solvent ternary blends on a heterogeneously functionalized substrate

Phase separation of bisphenol A polycarbonate (PC) and poly(methyl methacrylate) (PMMA) thin blend film is suppressed by addition of solid epoxy oligomer. Epoxy has strong intermolecular interactions with both PC and PMMA, while PC and PMMA are quite incompatible with each other. Consequently, phase separation in the PC/PMMA blend film pushes epoxy to the interface; at the same time, PC and epoxy react readily at the interface to form a cross-linking structure, binding PMMA chains together. Therefore, the interface between PC and PMMA is effectively reinforced, and the PC/PMMA thin blend film is stabilized against phase separation. On the other hand, only an optimal content of epoxy (i.e., 10 wt %) can serve as an efficient interfacial agent. In contrast to the traditional reactive compatibilization, here we observed that the cross-linking structure along the interface is much more stable than block or graft copolymers. Atomic force microscopy (AFM) is used to characterize the morphological changes of the blend films as a function of annealing time. Two-dimensional fast Fourier transform (2D-FFT) of AFM data allows quantitative investigation of the scaling behavior of phase separation kinetics.

Suppression of Phase Separation in PC/PMMA Blend Film by Thermoset Oligomer

We have studied kinetics of polymerization-induced phase separation of epoxy solution in oligoethylene glycol using light scattering and an optical microscope. It was found that special double droplet morphology was observed only in a very narrow range of epoxy fraction, which depended on the reaction temperature. In the narrow range the phase separation rate was very fast, and the bicontinuous structure which was typical in spinodal decomposition-type phase separation was observed only in the very early stage, suggesting that the solutions in the narrow fraction range entered directly the spinodal decomposition region without crossing the bimodal region. It is therefore considered that the temperature-dependent narrow fraction range corresponds to the trajectory of the critical point of the phase separation curve in the fraction–temperature diagram.

Trajectory of Critical Point in Polymerization-Induced Phase Separation of Epoxy/Oligoethylene Glycol Solutions

In this paper, computer simulation results of phase separation dynamics of ternary mixture (A, B, and C) coupled with an interfacial chemical reaction A + BdC in two-dimension are presented. The effect of reduction of interfacial free energy due to the presence of species C along the interface is taken into consideration in our study. In the case of fixed domain size, it is shown in simulations that for both reversible and irreversible reactions the generation of species C is not affected by the reaction rate constants, and it is a diffusioncontrolled process. Also, the simulation reveals that for reversible chemical reaction in the case of fixed domain size, the equilibrium of concentrations is established. In the cases of coupling between domain growth and reversible reaction kinetics, it is shown in simulations that the domain growth eventually freezes regardless of the magnitude of the reaction rate constants. The higher the reaction rate constants are, the slower the evolution to reach the reach steady state is, the larger the steady state domain size is, and the smaller the average concentration of species C is.

Hongdong Zhang

Papers

Phase Separation Dynamics and Reaction Kinetics of Ternary Mixture Coupled with Interfacial Chemical Reaction