Monte Carlo Study On Phase Behaviors Of Polymer Blends In Thin Films

Polymer blends integrate the excellent physical and chemical properties of the individual components, which have great potential to construct nanostructure and to be functional materials. Polymer nanocomposite materials combine chemical and physical performance both of polymer matrix and nanoscale particles. It will be one of effective way to use the ability of self-assembly of block polymer in the bulk and solution state to control and well-organize the distribution of nanoparticles in polymer matrix. Monte Carlo method as a molecular/mesoscopic scale simulation method has a huge application field to research uncertainty and random problems in polymer science. In this thesis, the microscopic phase behavior of multicomponent blending systems with different chain sequence structures and diblock copolymer nanocomposite systems in thin film were studied by Monte Carlo simulation.1. Using Monte Carlo simulation, we observed the microphase separation behaviors of various polymer blends formed by diblock copolymer(A12B12), alternating copolymer((A1B1)12、(A4B4)3), and/or homopolymer(A24、B24)in thin films. In the study, we found that the blends of components with different chain sequences can form special microphase separated structure from inside to the surfaces of the film, which forms a vertical gradient structure. The effect of thin films parameters on the vertical gradient structure are studied in detail, such as film thickness, composition, interaction strength between A and B segment, kinds of components, as well as surface fields by substrates. We found that the surface fields have a great influence to the microstructure in thin film. The influence of surface field decreases correspondently with film thickness increasing. This shows that the molecular chain conformation entropy plays a principal role on the final assembly structure of blending systems in thick films.2. Using Monte Carlo simulation, we investigated the microphase behaviors of selective nanoparticles/diblock copolymer nanocomposites confined between two neutral surfaces. A series of phase diagrams for copolymer nanocomposites microphase separation under varied film thicknesses were constructed. With nanoparticle concentration increasing, we observed structures transition from lamella to perforated lamella, cylinder, and sphere in the film. The orientation of the microstructure and the size of microphase space in the phase diagram are strongly affected by system parameters. We calculated the nanoparticles pair distribution function. At low nanoparticle concentration, nanoparticles gradually distribute in the central region of lamellar microdomain with nanoparticle selective interaction strength increasing. We showed that the distribution of nanoparticles in lamellar microphase can be controlled by the adjustment of nanoparticles selective strength to different copolymer blocks. On the other hand, in order to study the impact of the selective nanoparticlet to the configuration of copolymer chain, we calculated the Re and Rg of copolymer chain. We also examined the evolution of chain configuration and those of separated blocks as nanoparticle concentration and selectivity strength varying. In the process of phase transition, the changes of configuration of different blocks have a different contribution to the evolution of chain configuration.