| The control of particle sizes in polymer blends is vital to the ultimate physical properties of a blend. Understanding the phenomena which contribute to particle growth will aid in the intelligent design of polymer blends. In order to gain insight into these mechanisms, coalescence and the late stage coarsening of particulate polymer blends were investigated using a nonlinear diffusion model of the Cahn-Hilliard type. In ternary blends, the third component was chosen to be a compatibilizer, typically a random copolymer of the major components.; Numerical simulations were used to determine coalescence times in binary particulate and ternary core-shell systems as a function of particle separation, component diffusivity, and component chain length. Coalescence times increased sharply with initial particle separation. There is an effective upper limit for initial separation, beyond which coalescence does not occur in quiescent systems. This upper limit is much larger than that calculated using the theory of van der Waals interactions, thus demonstrating the importance of diffusion as a rupture mechanism. The extension of the coalescence simulations to ternary systems showed the compatibilization which results from the addition of a third component in a core-shell morphology. Coalescence times in both systems were found to be sensitive to chain lengths, which affect both the thermodynamics and component diffusivities.; In ternary systems, numerical simulations of late stage coarsening showed that compatibilized blends follow the same Lifshitz-Slyozov-Wagner coarsening law as binary systems. Slower coarsening rates, indicating system stabilization, were observed for blends containing 10–15% compatibilizer and exhibiting a core-shell morphology. These results compare favorably with experimental studies which used block copolymers as compatibilizers. As in the coalescence study, coarsening rates were sensitive to component chain lengths. The combined results demonstrate the importance of selecting components with specific properties when controlling particle growth in polymer blends. |
