Hierarchical Self-Assembly of PS-b-P4VP/PS-b-PNIPAM Mixture into Multicompartment Micelles and Its Response to Two-Dimensional Confinements
Hierarchical self-assembly offers an elegant and energy-efficient bottom-up strategy for the fabrication of complex materials with precisely controllable morphologies and internal structures. Herein, pupa-like multicompartment micelles (MCMs) were readily fabricated via the hierarchical self-assembly of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and polystyrene-block-poly(N-isopropylacrylamide) (PS-b-PNIPAM) block copolymers mixture in THF/water mixture solvent, which were unable to obtained by any of the individual block copolymers (BCPs). This means that the hierarchical self-assembly is a result by the synergistic cooperation of the two block copolymers. Moreover, a kinetic study revealed that the MCMs were formed by hierarchical self-assembly of small spherical micelles (SSMs) which were co-assembled from PS-b-P4VP/PS-b-PNIPAM mixture. Subsequently, we investigated the self-assembly of PS-b-P4VP/PS-b-PNIPAM mixed solution confined in the nanopores of the anodic aluminum oxide (AAO) template. In such two-dimensional confinement, long multicompartment micelles (LMCMs) with a period multilayer structure were obtained. Notably, the confinement effect of nanopores on the hierarchical self-assembly could be distinguished into two different situations according to the activity for secondary assembly of preformed SSMs from different BCPs compositions, i.e., the dynamic and static confinement. The dynamic confinement can affect the Brownian movement of SSMs and thus promotes their fusion to form spherical micelles with larger size comparing with the SSMs formed under unconfined condition. For the situation that AAO nanopores were partially filled with the preformed SSMs, the static confinement could decrease the stretching of BCPs chains along the short axis of LMCMs and thus induce the formation of long range ordered multilayer nanostructures. These results illustrated that the synergistic effect played an important role in the hierarchical assembly of block copolymers, meanwhile, such hierarchical self-assembly could be further manipulated by cylindrical confinement to rationally tune the nanostructures and dimensions of the BCPs assemblies.