SIMULATION OF THE FORMATION OF MICELLES BY DIBLOCK COPOLYMERS UNDER WEAK SEGREGATION

Simulation of the self-assembly of diblock copolymers, A(NA)B(NB), into micelles has been performed on a cubic lattice. In all calculations, the pairwise energy of interaction of A with B is identical with the pairwise interaction (E(AS)) of A with a void (solvent). With this assignment of the energies, the critical micelle concentration (cmc) depends strongly on N(A) and the interaction parameter, which is denoted as chi. The cmc is weakly dependent on N(B) if it is expressed in terms of the volume fraction of A, and N(B) is not too different from N(A). The cmc is determined for the conditions 3 < (chi/z)N(A) < 6, where z is the lattice constant. In this range, the cmc shows an exponential dependence on chi(N)A, partial derivative In V(A)cmc/partial derivative [(chi/z)N(A)] almost-equal-to -1.2. At constant chi(N)A, the value of V(A)cmc increases slightly when N(A) decreases. In the micelles the insoluble block is slightly collapsed, and the soluble block becomes stretched as N(B) increases, with N(A) and the number of chains in the micelle held constant. The size of the micelle is close to that estimated by a simple hard-core shell model.