A - B diblock copolymer micelles: Effects of soluble-block length and component compatibility

Micellization of a diblock copolymer in dilute solution is studied by dissipative particle dynamics. The influence of the compatibility between blocks A and B and the interaction between the insoluble block and solvent on aggregation number P and micellar core radius R_c are examined. The micelle size distribution is obtained, and it is quite polydisperse. Different from the scaling theory for starlike micelles, the mean aggregation number based on weight average (P)_w decreases with increasing soluble-block length N_A and the power law relation can be obtained, (P)_w ∼ N_A^-α Similarly, the micellar core radius declines with N_A, following R_c ∼ A_A ^-β with β = α/3. However, the exponent depends on the mutual compatibility between soluble and insoluble blocks. For the same composition, the incompatible diblocks form a smaller micelle and its aggregation number declines with a smaller exponent a. When N_A ∼ N_B, the micelles deviate significantly from the spherical shape and solvophilic blocks are observed to be entrapped in the solvophobic core for compatible diblocks.