Theoretical Simulation On Conformation And Self-Assembly Of Polymers In Confined States

Confinement of polymers widely exists in many applications, such as, polymer alloys, drug control-release of polymers, stabilization of colloids of polymers. The confinement can be in thin film, on substrates, in the interfaces between polymers and air or other components, even in different geometries. Structural properties and phase behaviors of free polymer chains in solutions or melts are studied widely and intensively. Recently, the conformation and morphology of polymers have become one of the important and attractive areas. In the thesis, the structural properties and self-assembly of polymers in confined states are simulated by Monte Carlo method and Self-consistent Field Theory.Structural properties of a polymer melt confined in nanocylinders are investigated by Monte Carlo simulation, which was successfully used to consider the conformational property of constrained polymer glass. The conformational properties of the polymers close to the inside walls exhibit the different features. There are several maxima near the wall, which shows that distribution of the polymer in the nanocylinder is not universe. The density profiles of the monomers are enhanced at the inner wall of the nanocylinder and decay toward the bulk value. Due to the confinement effect near the wall, the distribution of polymers has local maxima. Therefore, the density of the chains near the wall is higher. That is to say, the nanopore confinement causes the different packing densities near the wall and far from the wall. Comparing the highest densities near the inside wall of the nanocylinder, we can find that the highest density decreases with increasing the radius of the nanopore. At the lower temperature, the density excess is not only near inner wall of the nanotube, but also shifts to the center of the nanocylinder when the radius of the nanocylinder is very small. The radius of gyration and the bond length of polymers in the nanocylinder show that the polymer chains tend to extend along the axis of the nanocylinder in highly confined nanocylinder and contract at lower temperature. The above results are very helpful in understanding the different packing information induced physical behaviors of polymers in nanocylinders, such as glass transition, crystallization, etc.The morphology and the phase diagram of ABC triblock copolymer thin film directed by polymer brushes are investigated by the self-consistent field theory in three dimensions. The polymer brushes coated on the substrate can be used as a good soft template to tailor the morphology of the block copolymer thin films compared with those on the hard substrates. By continuously changing the composition of the block copolymer, the phase diagrams are constructed for three cases with the fixed film thickness and the brush density:identical interaction parameters, frustrated and non-frustrated cases. Some ordered complex morphologies are observed:parallel lamellar phase with hexagonally packed pores at surfaces (LAM3//-HFs), perpendicular lamellar phase with cylinders at the interface (LAM⊥-CI), and perpendicular hexagonally packed cylinders phase with rings at the interface (C2⊥-RI). A desired direction (perpendicular or parallel to the coated surfaces) of lamellar phases or cylindrical phases can be obtained by varying the composition and the interactions between different blocks. The phase diagram of ABC triblock copolymer thin film wetted between the polymer brush-coated surfaces are very useful in designing the directed pattern of ABC triblock copolymer thin film.The crowding agent induced disorder to order phase transition of amphiphilic block copolymers in solution was explicitly considered. The influences of the size and the volume fraction of the crowding agent on the phase separation of amphiphilic diblock copolymers are investigated by using self-consistent field theory (SCFT) method. The concentration of the disorder to order transition of the block copolymer decreases when the size of the crowding agent is larger than that of the solvent. The higher volume fraction of the crowding agent will induce the transition of the block copolymer from disorder to order state at a lower concentration. The relation between the size and the volume fraction of the crowding agent is elucidated. When the size of the crowding agent is larger, its volume fraction of the disorder to order transition of the block copolymer will be lower.