Formation of microdomain structures in concentrated systems of irregular (stochastic) copolymers with weak composition asymmetry $(ϵ⪡1)$ is considered theoretically. The study is focused on the weak segregation regime for infinitely long copolymer chains near the disorder-to-order transition. It is shown that the transition occurs below the spinodal (at ${\chi }_0<{\chi }^{*}$) and that it results in the formation of micelles rather than in a superposition pattern of a few harmonic composition waves. The micelle size is inversely proportional to $\Delta \chi =\chi -{\chi }_0$. For small $\Delta \chi$ the micelles are like large nearly uniform droplets with “reflected” composition, $-ϵ$. As $\Delta \chi$ increases the micelle composition profile develops oscillations. A first-order transition from spherical-wave micelles to micelles with internal bcc structure is predicted at $\chi ∕{\chi }^{*}-1\propto {ϵ}^2$. Interaction of micelles is also considered. It is shown that micelles always tend to form a fcc superlattice. The micellization in the weak segregation regime is controlled by the so-called nonlocal free energy. The classical fourth order (in composition parameter $A$) approximation for this energy is significantly generalized in the regime of low volume fraction of micelles. It is shown that the nonlocal energy strongly (exponentially) increases with $A$ near and above a certain critical value $A\simeq A^{*}$.

• Received 13 May 2005

DOI:https://doi.org/10.1103/PhysRevE.73.041803