Computer Simulation On Self-Assembly Structure And Dynamics Properties Of Confined Polymers

The self-assembly,conformation and dynamical properties of polymers under confinements are important research topics in the field of soft matter.Since the spatial constraint and the interaction of the confinement with polymers,the confined polymers exhibit completely different behavior from the bulk.Therefore,confinements are often adopted to achieve precise control of the orientation and structure of copolymers.However,it is difficult to analyze the dynamic process in experiments.In this thesis,computer simulations are performed to systematically investigate the behavior of polymers under one-dimension and two-dimension confinements.It is divided into two parts as follows:(1)Self-assembly of rod-coil(RC)symmetric diblock copolymers(DBCs)in a cylindrical nanopore is investigated by performing dissipative particle dynamics simulation.A morphological phase diagram of R6C6 DBCs with respect to the property and diameter of pore is presented.In nonselective and weak rod-selective pores,stacked disks,single helix,and double helix are assembled.While in strong rod-selective nanopores,coil blocks assemble into stacked disks,cylinder,and then zigzag structure in the interior region of pore with the increase in the pore diameter.The zigzag structure evolves into curb chain-like structure,corrugated pipe and single helix tube with further increase in the pore diameter.The zigzag structure is induced by the movement of rod blocks toward the pore surface and subsequent assembly near the surface.At last,a morphological phase diagram in terms of the block length and the pore diameter is obtained.Our simulation results demonstrate that the synergetic interaction among the rigidity of the rod block,the incommensurability of the pore diameter,and the preference of the pore surface for the rod block,plays an important role in the assembly of RC DBCs.(2)The conformation and dynamic behavior of homopolymers within a slit are studied based on coarse-grained molecular dynamics simulation.The effects of the slit thickness,the concentration and chain length of homopolymers are investigated.For the polymers with small concentrations,they undergo a variation from the flexible coil in bulk to compression,and then to expension with the decrease in the slit thickness.The mean square radius of gyration first decreases and then increases with the decrease in the slit thickness.However,the stretching trend is not observed in polymers with high concentrations.There are two kinds of kinetic behaviors in polymer solution: Rouse model(non-entanglement)for polymers with the chain length N < 80 and Reptation model(entanglement)with N > 80.For the confined non-entanglement polymer chains,the relaxation time τ is always longer than that in solution.However,the variation of the self-diffusion coefficient DXY depends on the concentration c.At small c,DXY first decreases and then increases with the increase in the chain length and the decrease in the slit thickness.While DXY always decreases at big c.It demonstrates that the movement of polymer chains is inhibited by the spatial constraint and chain interaction.For the confined entanglement polymer chains,a similar variation is observed at small c.However,at big c,the movement of polymer chains first accelerates and then slows down with the increase in the chain length and the decrease in the slit thickness.The result manifests the competition between the spatial constraint and the chain entanglement.