SCFT simulation and SANS study on spatial distribution of solvents in microphase separation induced by a differentiating non-solvent in a semi-dilute solution of an ultra-high-molecular-weight block copolymer

Lyotropic order-disorder transition (ODT) in a semi-dilute solution of an ultra-high-molecular-weight block copolymer using a neutral solvent and a differentiating non-solvent was investigated. The role of the differentiating non-solvent in the ODT was revealed by the spatial distribution of the solvents simulated theoretically by the self-consistent field (SCF) theory approach and demonstrated experimentally by small-angle neutron scattering (SANS). The solutions of polystyrene-block-poly (tert-butyl methacrylate) (PS-b-PtBuMA) with an ultra-high-molecular-weight (UHMW) in a mixture of tetrahydrofuran (THF)/ water as a good and neutral solvent and a differentiating non-solvent, respectively, were used. The contrast variation method by SANS experimentally demonstrated that THF and water collectively move into the PtBuMA phase and that the volume fraction ratios of water to THF in both phases are almost equivalent to each other. This means that the solvent mixture of THF and water behaves as a single and strongly selective solvent. The collective movement of the solvents was well reproduced by the simulation. Interestingly, it was also suggested that THF gather in the vicinity of styrene-(tert-butyl methacrylate) interface to shield the unfavorable strong interaction between the PS and the PtBuMA phases and that water gather in the center of the PtBuMA phase to decrease the unfavorable contact with the PS phase.