A Monte Carlo simulation for the micellization of ABA- and BAB-type triblock copolymers in a selective solvent

The micellization behaviors of ABA and BAB triblock copolymers in a solvent selective for block A are investigated by means of grand canonical Monte C arlo (GCMG) simulation. The basic micellar parameters such as the micellar size, its distribution, the micellar shape, and the internal structure of m icelles are obtained and compared for both systems. The critical micelle co ncentrations (cmc) are quantitatively estimated from the osmotic pressure o btained by the GCMG simulation combined with the multiple histogram method. The results of simulation show that the chain architecture of the triblock copolymers shows large differences in their association behavior in a sele ctive solvent, although both copolymers have the same composition and total chain length. The thermodynamic analysis confirms that an additional entro py loss due to the looping conformation of the middle block of BAB copolyme r induces a higher cmc value and therefore reduces the capability to self-a ssemble into micelles. As a result, the BAB copolymer chain may have variou s chain topology such as dangling, loop, and bridge chains in micelles. Fro m the multiple equilibrium model, it is possible to extract the entropy ass ociated with packing the chains into a micelle for two different systems. T he BAB copolymer yields less negative packing entropy due to less order of micelles by the presence of the dangling and bridge chains as compared with ABA copolymer, which results in micelles with larger sizes and a broader s ize distribution despite its high cmc value.