Influence Of Blending On Self Assembly Of Block Copolymer

Self assembly of block copolymer can be conducted in solvent, thin film and bulk, and ordered structures in nano-scale can be achieved. As a creative method of material processing and synthesis, self assembly gains lots of interests in the fields of chemistry, material and biology. Among three self assembly systems, the self assembly in solution and thin film are the emphasis of research and application for its advantages of convenience in operation, controllable experimental factors and lower costs.Block copolymers of PS-PEO (Polystyrene-b-polyoxyethylene) and PS-P2VP (Polystyrene-b-Poly (2-vinylpyridine)) have a hydrophilic block and a hydrophobic block, so self assembly is expected in selective solvent and thin film, and a series of regular self assembly structures can be achieved through the adjustment of factors like blending, solvent conditions and annealing conditions. The study of them would be a great improvement of theoretical research and application of block copolymer self assembly. And based on the above mentions, block copolymer PS-PEO and PS-P2VP were studied in our project. We have studied the influence of blending ratio and solvent/vapor conditions on the self assemble process of copolymer mixture in selective solvent and thin film. The self assembly structures were analyzed by Atomic Force Microscope (AFM), and a novel structure theory was put forward about the influence factors on the self assembly structure. From the experimental results, following conclusions were drawn:(1) In the self assembly process of block-copolymers in selective solvents, the solubility of PS-PEO in ethanol-chloroform mixture is improved by the addition of PS-P2VP, and the morphology and the size of micelles can be controlled by changing the molecular weight and blending ratio of PS-P2VP.1) The copolymer that could not assemble or dissolve in solvent is able to be coerced by copolymers that could completely assemble in solvent to form complete self-assembled structure;2) In blending system, the size of micelles increase with increasing ratio of copolymers that could not assemble or dissolve in solvent;3) The capability of copolymers that could completely assemble in solvent coercing copolymers that could not assemble or dissolve in solvent is limited:about the molar ratio of1:1according to the date;4) the involvement of copolymers that could not assemble or dissolve in solvent will change the structure of micelles of the copolymer that could completely assemble in solvent: increasing the size of micelles when the ratio in approaching the molar ratio of1:1, and over that ratio, the excess copolymers that could not assemble or dissolve in solvent would form irregular structures similar to structures when processed in solvent along.(2) In the self assembly of block-copolymers PS56K-P2VP21K and PS23.6K-P2VPio.4K mixture in thin film, blending ratio and solvent/vapor conditions are good controlling factors over the self assembly structure.1) In the annealing self assembly process, phase separation of copolymers with larger molecular weight was influenced by its degree of moving freedom and restricted in smaller domain, and phase separation will be improved if mixed with copolymers with smaller molecular weight;2) The better solvent for block that preferentially absorbed on substrate could promote the phase separation in the process of annealing self assembly in thin film;3) If two kinds of copolymers can form structures of different types when annealed separately, then the mixture will form the structure correspondent to the copolymer with larger ratio, and transition morphology can be observed at the blending ratio of1:1wt%approximately;4) If two kinds of copolymers can form structures of the same type when annealed separately, then the mixture will result in the structure of that type, and the size commit a transitional behaviour with the ratio between the size of structures formed separately;5) The influence of vapor on annealing self assembly is very efficient, phase separation can be easily introduced if vapor is selective for the smaller molecular weight block of copolymer and hardly achieved to the contrary.