Fabrication of polymer nanospheres based on rayleigh instability in capillary channels

We report a simple method to produce block copolymer nanospheres by swelling the short rodlike entities generated from Rayleigh instability of polymer nanotubes within the cylindrical nanopores of an anodic aluminum oxide (AAO) membrane. Poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) nanotubes were first allowed to form inside the cylindrical nanopores through solution-wetting of an AAO membrane followed by solvent evaporation. Upon thermal annealing, undulations in the nanotube wall occurred due to Rayleigh instability and finally led to the formation of nanorods containing regular encapsulated holes. The structures were susceptible to ultrasonication and could be cut into short rodlike blocks with uniform size. These PS-b-P2VP entities were suspended in water with the help of a nonionic surfactant and then swollen by a good solvent for both PS and P2VP. The swollen PS-b-P2VP entities were deformable and spontaneously evolved into nanospheres so as to minimize the interfacial energy. The characterization of the nanospheres by transmission electron microscopy confirmed that the swollen PS-b-P2VP could microphase-separate into an ordered structure under three-dimensional confinement. Furthermore, the selective swelling of P2VP within the PS-b-P2VP nanospheres by ethanol/HCl mixture yielded the internal structural reconstruction and the formation of mesoporous nanospheres. The obtained mesoporous nanospheres of PS-b-P2VP may be useful as nanocontainers in the application of supporting catalyst.