Toroid formation through self-assembly of graft copolymer and homopolymer mixtures: experimental studies and dissipative particle dynamics simulations.

Self-assembly of mixture systems containing poly(acrylic acid)-g-poly(γ-benzyl-L-glutamate) graft copolymers (PAA-g-PBLG) and PBLG homopolymers in aqueous solution was investigated by both experiments and computer simulations. It was found that the aggregate morphologies, such as rods, curved rods, and toroids, could be tuned by the homopolymer content. The toroidal micelles with uniform size were formed when the homopolymer content in the hybrid aggregates is higher. The effect of added water content on the toroid formation process was studied. Rods and curved rods were observed sequentially before formation of toroids. We also performed dissipative particle dynamics (DPD) simulations to verify the structure transition and explore the formation mechanism of the toroidal aggregates. The DPD results are in good agreement with the experimental findings and provide additional information such as chain distribution in aggregates, which is difficult to be gained through experiments. On the basis of the experimental and simulation results, the formation mechanism of the toroidal micelles was suggested.