Tuning polymer micelle size and dynamics with solvophobic block structure

Abstract

Hypothesis: Micelles formed by copolymers with mixed solvophobic blocks have attracted much attention lately. It is expected that changing the mixed blocks sequence can be used as a tool to influence the micellization behavior in a way that is not equivalent to simply varying the incompatibility parameter for pure diblock-copolymers.

Simulations: By using coarse-grained simulations, the micellization behavior of copolymers with twelve types of solvophobic blocks, which differed in the fraction f as well as the sequence of solvophilic units in the solvophobic blocks, was studied. To enable quantitative comparison of systems with different f, an “effective” incompatibility parameter was introduced.

Findings: The micelles size distributions and dynamics were found to be significantly dependent on both f and the fine details of the sequence. When the solvophobic block sequences were obtained statistically using a model of copolymerization, a strong influence of the reactivity ratios on the resulting micelles was found. Even a moderate tendency to form gradient-like sequences resulted in a noticeable increase in the micelles size. The dynamic properties of the micelles were studied by investigating the rate at which the chains escape from them. The addition of soluble units into the solvophobic block was shown to dramatically decrease the tendency to form kinetically frozen states; gradient-like sequences demonstrated more sluggish dynamics. The physical reasons for the observed peculiarities are discussed in detail.