Aggregation processes in self-associating polymer systems: A comparative analysis of theoretical and computer simulation data for micelles in the superstrong segregation regime

We present an extension of our previous theory describing aggregation processes in self-associating polymer systems, i.e., in copolymers with strongly attracting groups. In particular, the formation and properties of micelles are studied in detail for the superstrong segregation regime. We have explicitly taken into account the effect of the radius of attraction, r(c), and the structural defects of the micellar core on the micellar shape and stability. It has been shown that for a given aggregation number, Q, the shape of the micellar core is determined by a balance between the interfacial free energy and the energy of structural defects. As the effective energy of attraction increases, the most stable shape of the core can change from spherical to disk-like (oblate ellipsoid). A transition between spherical and disk-like core geometries takes place at nearly equal interfacial and defect free energies. In the case of long-range attraction (i.e., for large r(c)), we have shown that the surface term must dominate, thus stabilizing a spherical shape of the core. Alternatively, for small r(c), the non-spherical (disk-like) geometry of the micellar core becomes most stable. The critical radius of transition, r(c)*, theoretically predicted, is in a reasonable agreement with computer simulations presented in our previous paper. If r(c) is further decreased and the effective energy of attraction is fixed, then the large aggregate can disintegrate and form smaller disk-like splinters. We have located this equilibrium transition point. The critical value r(c)** thus obtained is in very good agreement with molecular dynamics calculations performed by us. At last, the theory predicts the formation of strongly elongated (stripe-like) micelles in concentrated solutions. Such structures were also observed in our computer experiments.