Simulated Annealing Study Of Self-Assembly Of Grafted Polymers And Confined Diblock Copolymers In Solution

The polymer solution under a complex environment could form many novel microstructures,which have great application value in the preparation of surface functional materials and nano-mesoporous materials.In this thesis,Simulated Annealing is used to investigate the self-assembly behaviors of the blends of grafted homopolymers and free copolymers and diblock copolymer under a cylinder confinement in selective solution.In chapter one,we briefly introduced the concept of soft matter and the background of the diblock copolymer researches in a confined system.Then we introduced the Monte Carlo method involved in the study and the framework of the thesis.In chapter two,we investigated the co-assembly behaviors of the mixture system with AB diblock copolymers(BCPs)and plate-grafted A-homopolymer brushes(HP),based on the basis of the experiments of the co-assembly of linear PS-b-PDMAEMA diblock copolymer and PS homopolymer brushes on nanosilica particles.There are two competing assembled processes: AB diblock copolymers and A-brushes coassemble into surface micelles(s-micelles)with collapsed A-monomer core and B-monomer coronae.Meanwhile,BCP self-assemble into free block copolymer micelles(b-micelles)in solvents.Our simulation results show that the concentration of BCP,the grafting density of HP,the length of BCP chains,and the length of HP brushes all have influenced on the co-assembly process.The average size of s-micelles increase with BCP concentration in low BCP concentrations areas and then keeps unchanged at high concentration.With the increase of the length of the Solvophobic A-blocks,the average size of s-micelles will increase significantly.The length of the hydrophilic B-blocks exert a certain effect on the morphology of s-micelles.When the length of B chain is short,they assembled to stripe-like s-micelles.With the increase of the B-block length,The morphology of s-micelles transition from stripes to a coexistence of wormlike/hemispherical micelles and form smaller hemispherical micelles.The average size of s-micelles at higher graft densities is greater than that at low graft density.In addition,with the increase of HP brushes,s-micelles change from separated spherical micelles to striped micelles.In chapter three,we studied the arrangement of spherical micelles self-assembled by the BCP solution in a cylinder.A13B3 was selected as the object to investigate the influence of the radius of the cyliner(r),the selective intensity of the pore wall(εW)and the selective intensity of the solvents(εS)on the arrangement of the spherical micelles.The simulation results demostrate that r,εW and εS can change the arrangement of the spherical micelles.In a selective nano-cylinder system,the micelles formed by A13B3 are arranged in a single layer structure when the r is small,including the linear structure,zigzag structure,or a single-layer spiral structure which could be marked by the phyllotactic description(m+n,m,n),where m+n named the primary leaf number,m called the second leaf number,n called the third leaf number and m ≥ n.With the increases of r,the phase structure shifts toward the direction of the increase of the primary phyllotactic number,satisfying the ―basic phase transition sequence‖: linear → zigzag →(2,2,0)→(3,2,1)→(3,3,0)→(4,2,2)→(4,3,1)→(4,4,0)→(5,3,2)→(5,4,1)→(5,5,0)→(6,3,3).When the r is large enough,micelles form a double-layer structure with a linear structure inside and a helix strcuture outside.It is worth noting that the primary phyllotactic number of the outside arrangement starting from 6,mainly(6,5,1)arrangement and(6,3,3)arrangement,marked as(6,5,1)&linear and(6,3,3)&linear.There is no(6,6,0)&linear structure observed.By increasing εW,the single helix layer structure transform to new phase structure with biger primary phyllotactic number.However,the specific arrangement is influenced by the mutual competition mechanism between the selectivity to A-monomer and the repulsion to B-monomer of the pore wall.With increasing the εS,the single-layer helix phase structure changes to the phase structure in which the main phyllotactic number or the second phyllotactic number decreases in the case of the r being larger.In addition,in the Chapter three,we also simulated the phase structure of the micelle arrangement under the neutral pore environment.The hydrophobic B-monomers form disk-like micelles on the cylindrical wall and the micelles still has a phase structure with a spiral arrangement.There is an "irregular phase transition sequence" :zigzag →(2,2,0)→(3,2,1)→(3,3,0)→(4,2,2)→(4,3,1)→(4,4,0)&linear→(5,5,0)&linear →(6,6,0)&linear,which is obviously different with that in the selective system.There are no linear and mono-layer structure,such as(4,4,0),(5,3,2),(5,4,1)and(6,3,3)in the irregular phase transition sequence.the double-layer achiral structure,which has the same number of the first and the second phyllotactic number in outer helix,appear directly after the single-layer helix structure with the first phyllotactic number equal to 4.Our simulation results are consistent with the relevant experimental results basically.We hope to verify,help and guide the experiments to obtain novel,useful microscopically ordered materials by the copolymers self-assembling under the right circumstances.