Scaling and domain growth in ternary amphiphilic systems.

摘要

Phase separation in binary systems leads to domain growth. The characteristic domain size, R, usually follows a power growth law, R ∝ tn, where t is time and n is the scaling exponent. The value of n depends on a variety of factors including the number of physical dimensions, the presence of hydrodynamic interactions, and the relative concentration of the two phases. Power law behavior is observed in binary metallic alloys, oil/water mixtures and binary polymer blends.; The addition of a third, compatibilizing component, such as a surfactant into an oil/water mixture, or a block copolymer A-B into a binary polymer blend A/B, alters the dynamics of domain growth. Such ternary systems usually follow power law curves with smaller exponents than observed binary system, and some studies have reported altogether different scaling laws.; Lattice Monte Carlo and dissipative particle dynamics simulations were performed to study the phase separation behavior of ternary amphiphilic systems (systems of type A/B/A-B). The two simulation techniques gave similar results. The late stages of domain growth followed power law behavior. Scaling exponents are reported as a function of the amount of amphiphile, the nature of the amphiphile, and the relative concentration of the two phases. It was found that symmetric amphiphiles are better interfacial agents than asymmetric amphiphiles. It was also found that longer amphiphiles were better interfacial agents.; Experiments were performed on polystyrene/polybutadiene/block-copolymer blends to study the domain growth characteristics. Bulk blends were produced using a solution blending technique called compositional quenching. The blends were characterized using transmission electron microscopy and domain sizes were calculated. The experiments showed that the ternary blends followed the power law of growth. The results from the simulations were in reasonable agreement with the experiments. Izod impact studies were done to study the effect of copolymer properties on the impact strength of ternary polymer blends.