Intramolecular Janus segregation of a heteroarm star copolymer

Conformations of heteroarm star copolymers A _nB _n are investigated by off-lattice Monte Carlo simulations. Intramolecular segregation is always observed in selective solvents. It can also be found in a common good solvent, which however gives block incompatibility. The degree of Janus segregation is characterized by the mean-square separation between A and B blocks, 〈(X _A - X _B) ²〉, or by the orientation correlation between the two blocks, 〈X _A· X _B〉, where X _i denotes the relative position of the center of mass associated with the block arms i from the star core. The degree of segregation grows with increasing arm numbers while the effect of arm lengths is insignificant. The influence of the intramolecular segregation on the aggregation behavior in solution can be revealed through interactions between two star copolymers. The potential of mean force and second virial coefficient are calculated for various solvent qualities. In a selective solvent, the blockarm star copolymer can form a unimolecular micelle structure and always shows intermolecular repulsions. In contrast, the heteroarm star copolymer may display the Janus segregation, which leads to intermolecular attractions. This consequence facilitates the formation of multimolecular micelles.