| A polymer is a large molecule composed of one or several repeating structural units which are connected by covalent chemical bonds. Because of the complex structure, polymers with a wide variety of good properties have attracted more and more concerns and have been researched and applied in several areas. With the development of computer technology in recent years, computer simulations have also been regularly applied in polymer research. Because of the complex structure of polymers and the multi-scale nature of polymer composite, it is difficult to fully reflect all aspects of the system by using single computer simulation method. In this paper, the molecular dynamics (MD) and mesoscopic dynamics (MesoDyn) simulations are employed to investigate the processes and properties in several polymer systems including polymer blends, solution of polymeric surfactant and polymer-inorganic system. The main contents are as follows:(1) The blend of chitosan (CS) and polyethylene oxide (PEO) was simulated by molecular dynamics simulation (MD). The compatibility of polymer blend was investigated by Flory-Huggins parameter and glass transition temperature (Tg). The Flory-Huggins parameterχbetween CS and PEO was calculated both by solubility parameterδand mixing energyΔEmix The Flory-Huggins parameterχfirstly decreased and then almost kept steady with the increasing of temperature. We can find thatχvalue of 1/1 and 1/2 (chitosan/PEO) blends are larger thanχcritical in the whole temperature range which indicates these two blends are completely immiscible. However, other three blends are miscible when the temperature is over 300K.The blends with the compositions 3/1,2/1 and 1/3 (chitosan/PEO) have single Tg. However, the other two blends both have two Tg, which indicate that twice transitions will happen in PEO rich and CS rich regions at different temperature. Tg drawn by the result of MSD is similar with that deduced by specific volume. The chain models of PEO and CS molecule are conversed into bead-spring model which is used in Mesodyn simulation. The order parameters and density figures are investigated which prove that the blend system is incompatible when the content of two components is close.(2) Fully atomistic dynamics simulations had been performed to investigate the effects of temperature and solution concentration on the structure of tri-block polymeric surfactant Pluronic P65. Simulations were carried out covering a composition range of 0.1-0.8 and a temperature range of 273-373k.The Flory-Huggins interaction parameter, radial distribution function, mean-square displacements and fractional free volume were employed to analysis non-bond interactions, hydrogen bonding and the mobility of water and P65 segments in P65 aqueous solutions. The Flory-Huggins parameters indicated that propylene oxide (PO) segments became hydrophobic with the temperature increasing, while ethylene oxide (EO) segments still kept hydrophilic, which caused the increasing of repulsion force between EO and PO segments. There were two kinds of intermolecular hydrogen bonds in P65 aqueous solution which were water-water hydrogen bonds and water-P65 hydrogen bonds. The two kinds of hydrogen bonds both increased with the increasing of solution concentration and decreased with the increasing of temperature. The water-P65 hydrogen bonds were formed by water as hydrogen donors and P65 as hydrogen acceptors. The hydrogen bonding between EO segments and water was stronger than that between PO and water at the same composition. Moreover, the influence of temperature on the PO-water hydrogen bonds was larger than that of EO-water hydrogen bonds. The diffusion of water molecules includes two stages including anomalous diffusion and the Einstein diffusion, while the diffusion of polymer segments is purely anomalous diffusion. Besides, the increasing of temperature could shorten the stage of anomalous diffusion for water and increase the diffusion coefficient for both water and P65 segments. The CMTs of P65 were deduced in the range of 20-40oC which is consistent with the result reported by the literature.(3) The mesoscopic dynamic simulation (MesoDyn) has been carried out to investigate the phase structure and the aggregate properties of tri-block copolymers (ethylene oxide)37 (propylene oxide)56 (ethylene oxide)37(P105) in aqueous solution. A Gaussian chain model is successfully built according to the equivalent chain method and the Flory-Huggins interaction parametersχused for determining the repulsions between different chain segments are computed. Simulation results show that P105 can form several micro structures including spherical micelles, ellipsoid micellar cluster, worm-like micelles, defective bi-continuous phase and bi-continuous phase with its concentration increasing. A special transition phase structure of P105 is found in the spherical micellar region. The formation of micelle can be divided into four stages, including induction stage, pre-formation stage, evolution stage and the final equilibrium stage. The formation speed of micelles is discussed from two aspects including induction time and evolution speed which shows that the higher the concentration is, the faster the equilibrium state is achieved. The relation between solution concentration and density of micelles at equilibrium proves that the higher concentration of P105 will lead to less micelle with larger size. The two ways of micelles growth with time evolution are found by MesoDyn simulation. At relative low concentration, the diffusion of single dissolved P105 molecule is prevalent while at high concentration the coalescent of small micelles is dominant. In conclusion, mesoscopic simulation can be considered as an adjunct method for the description of mesoscale morphology formation and can give mesoscale information of complex system which can not be observed by experiments.(4) A novel and reasonable model of carbon black (CB) was built to investigate the surface modification of CB particles with PVA molecules by MD simulation and MesoDyn simulation. The modification process of PVA on CB surface was intuitively exhibited, which indicated that the encapsulation films were formed by stacking PVA molecules layer by layer on the surface of CB. The dispersion stability of unmodified and modified CB particles was compared both by simulation and by scanning electron microscope graphs. The simulation results indicated that surface modification had great effect on reducing the interaction energy of CB/water interface so as to alleviate agglomeration phenomenon significantly. Moreover, the influences of PVA amount on the morphology and the compatibility of PVA/CB interface were also investigated. The amount of PVA would neither influence the arrangement of single PVA molecule nor change the orientation of the single PVA layer but only decide the thickness of the modification film. Besides, the energy analysis results indicated that a suitable thickness of PVA coating could improve the dispersion stability of CB particles. The experiment results by SEM graphs and laser particle size analyzer had validated the simulation works.(5) Three methods are summarized for determining glass transition temperature of polymers by MD simulations and all these methods are applied to estimate the Tg of polyethylene oxide. The results of Tg are 248K by specific volume,275K by free volume ratio and 250K by chain mobility, which is consistent with the experiment data (200-256K) reported by other researchers. The effect of polymerization degree on Tg of polyethylene oxide are investigated by specific volume. The result shows that the Tg of PEO increases with the increasing of. This trend is obvious at low polymerization degree region. When polymerization degree reaches a certain value, the increment of Tg is negligible. Tg has a perfect linear relationship with the reciprocal of polymerization degree (R2=0.9801), which proves that the Tg of PEO by simulation accords with Fox-Flory equation, and the Tg of polymer with infinite molecular weight (Tg(∞)) is 257K. Besides, the effects of geometric isomerization on Tg is also discussed. The Tg of isotatic polymethyl methacrylate (PMMA) is 325K, while Tg of syndiotactic PMMA is 380K. The simulation results have good accordance with experiment data.
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