Self-assembly Of Amphiphilic Block Copolymers At The Interface

Amphiphilic block copolymers contain separate hydrophobic and hydrophilic portions, and exhibit abundant self-assembly behavior at the liquid/liquid interface. In our previous work, we successfully fabricated various catalytically active composite thin films of polymers with different morphologies and doped with noble metal nanoparticles at the liquid/liquid interface. The formation of these composites was regarded as a result of a specific adsorption process in which the special interaction between the polymer molecules and the inorganic species played a crucial role. In this work, we adapt polyisoprene-block-poly(2-vinylpyridine) (PI-b-P2VP) with a hydrophobic PI block that can be crosslinked by disulfur dichloride and obtained a pure polymer film that does not contain inorganic species at liquid/liquid interface of the polymer organic solution and pure water. We subsequently developed this liquid/liquid interface adsorption and self-assembly method by using a mixed DMF/CHCl3 solution as the organic phase instead of a CHCl3 solution, and we obtained multilayer thin films of polybutadiene-block-poly(4-vinylpyridine) (PB-b-P4VP) doped with Au nanoparticles at the air/water interface rather than at the liquid/liquid interface using this way. We also obtained composite multilayer and foam thin films of poly(2-vinylpyridine)-block-polystyrene-block-poly (2-vinylpyridine) (P2VP-b-PS-b-P2VP) and poly(4-vinylpyridine)-block-polystyrene-block-poly(4-vinylpyridine) (P4VP-b-PS-b-P4VP), respectively. This is a new and facile approach including mass transfer, self-assembly, and Gibbs adsorption steps. This method is expected to be useful to fabricate additional micro- and nanostructures of amphiphilic molecules, including block copolymers.1. Porous thin films of block copolymer fabricated at the liquid/liquid interfaceThree approaches have been utilized to fabricate thin composite films of amphiphilic PI-b-P2VP doped with silver and gold nanoparticles. Honeycomb and foam structures were obtained at the interfaces between a chloroform solution of the polymer and aqueous solutions of either AgNO3 or HAuCl4 through the first route. For the second route, porous thin films were obtained at the interfaces between a chloroform solution of the crosslinked polymer by S2Cl2 and pure water, immersed in aqueous solutions of either AgNO3 or HAuCl4 to adsorb metal precursors and then treated with KBH4 aqueous solution to form composite films. For the third route, porous thin films were obtained at the interfaces between a chloroform solution of the crosslinked polymer by S2Cl2 and aqueous solutions of inorganic metal ions. The catalytic properties of the films obtained using the first and second methods were evaluated by assessing the reduction of 4-nitrophenol by KBH4 in aqueous solutions. It was found that the metal nanoparticles are unstable enough and fused in the film prepared through the first route while the composite film obtained through the second route exhibited good catalytic performance and was more stable during the catalytic reaction. In addition, the porous polymer film is also expected to adsorb other species to form various functional composites.2. Catalytically active block copolymer/Au nanoparticle multilayer thin films fabricated at the air/liquid interface through a new and facile wayA composite polymer/Au nanoparticle multilayer film was fabricated at the air/liquid interface through a new and facile self-assembly and adsorption process. A planar liquid/liquid interface was formed at first by using a DMF/CHCl3 mixed solution of (PB-b-P4VP) as the lower phase and a HAuCl4 aqueous solution as the upper phase. The PB-b-P4VP molecules self organized into disk-like micelles in the mixed organic phase. Because DMF is miscible with water, DMF carried the block copolymer molecules and micelles into the upper aqueous phase, and then diffused into the HAuCl4 aqueous solution, leading to further self-assembly of the polymer molecules with the inorganic species and the formation of larger sheet aggregates. These aggregates further adsorbed at the air/liquid interface, resulting in the formation of the multilayer composite film. Most AuCl4- ions were reduced by DMF during this process, and numerous Au nanoparticles were generated and embedded in the composite film. This film exhibited unique heterogeneous catalytic properties due to its unique multilayer structure.3. Composite thin multilayered and foam films of block copolymers fabricated through the unique assembly approachComposite multilayer films of P2VP-b-PS-b-P2VP and composite foam films of P4VP-b-PS-b-P4VP were fabricated at the air/liquid interface through the unique and facile approach mentioned above, in which a planar liquid/liquid interface was formed at first by using a DMF/CHCl3 mixed solution of the polymer as the lower phase and a HAuCl4 aqueous solution as the upper phase, respectively. This was followed by mass transfer through the liquid/liquid interface and self-assembly in the upper phase as a result of what is known as the "ouzo effect." In the upper phase, disc-like micelles and microsheets of P2VP-b-PS-b-P2VP and microcapsules of P4VP-b-PS-b-P4VP were generated and adsorbed at the air/liquid interface before ultimately self-assembling into composite films. During this process, the AuCl4- ions bonded to the polymers and were reduced by DMF, thereby embedding numerous Au nanoparticles in both of the composite films. Interestingly, these two block copolymers exhibited different self-assembly behavior under similar conditions, leading to films with different morphologies.