Self-assembly Of ABA Triblock Copolymer Brushes In Selective Solvents

Polymer brushes are composed of flexible copolymer chains which are tethered onto a surface or interface by one end.Due to the self-assembly forms various structures,their extremely important role in the field of surface,have become one of the most attractive branches in polymer science.Compared with homopolymer brushes block copolymer brushes immersed in a selective solevent can from more complicated surface morphologies,because of the increased number of blocks.In this paper,we investigate the morphologies of ABA triblock copolymer brushes immersed in selective solvent using the simulated annealing method.The influences of grafting method,the block lengths,the grafting densities and interactions between different monomers on the morphology of the ABA triblock copolymer brushes have been investigated by constructing the phase diagram,showing snapshots of the morphologies,calculating the density profile of the monomers.In the first and second chapters of the paper,the research topics of the thesis,the model and method used in the research are introduced briefly,and the structural arrangement of the thesis is summarized.In chapter three,the simulated annealing method was used to study the self-assembly morphology of the symmetrical ABA triblock copolymer brush,formed by one end of the A-blocks tethered onto a planar surface,immersed in a selective solvent which is poor for the A-blocks but good for the middle B-blocks.Taking the system at high grafting density as an example,the morphology of the copolymer brush aggregates during uniformly grafting,local random grafting and global random grafting were investigated,and the phase diagram was constructed.The simulation studies have shown that for ABA triblock copolymer brushes the distribution of the position of the grafting point mainly affect the morphology of aggregates near the bottom layer.A similar self-assembled morphology can be formed during uniformly grafting,region random grafting,and global random grafting.However,the density fluctuation of the grafting point causes the micelle morphology formed under random grafting does not have the regular shape as that formed under uniformly grafting.And the long-range order in the microphase-segregated structures is reduced.The self-assembled morphologies of homopolymer brushes in poor solvent,and AB diblock copolymer brushes in the selective solvent which is selective for the tethered A-blocks but poor for the top B-blocks were also investigated,in order to further understand the results mentioned above.In chapter four,we investigate the morphologies and structural transitions of linear ABA triblock copolymer brushes immersed in a poor solvent using the simulated annealing method.Solvents are poor for both monomers A and B,and the mutual exclusion strength of the A monomer and the solvent is stronger.We performed systematic simulations at low grafting density,moderate grafting density,and high grafting density,and examined the effects of the block lengths and graft density on the self-assembly morphology.Then we simulated under different systems.The influence of the interaction between different monomers on the self-assembly morphology was investigated.It was found that with increase the length of blocks and graft density,the micelle morphology became richer,and morphological transitions from structures with only one A-rich layer to structures with two A-rich layers.It is found that the folding rate increases with the increase of?_AS,the system tends to form structures with only one A-rich layer.