Effect of the soluble block size on spherical diblock copolymer micelles

While the effect of the insoluble block length on micelle properties is well understood, the effect of the soluble block is still controversial. We, therefore, have investigated the effect of the molecular weight of the soluble block on the critical micelle concentration (CMC), aggregation number, and hydrodynamic radius of spherical polymer micelles. Spherical micelles were formed from polystyrene-b-polyisoprene (PS-b-PI) in heptane, which was a good solvent for PI and a poor solvent for PS. Measurements were performed on two series of PS-b-PI with a constant PS block (19 and 39 kDa, respectively) and PI blocks varying from 10 to 100 kDa. For samples with large PI blocks, the experimental data were found to be in agreement with the commonly used star-like model. However, the experimental data for samples with short PI blocks deviated from the crew-cut micelle model. To correctly capture the crossover between the crew-cut and star-like regimes, it was found necessary to use recently developed scaling theo...