Theoretical Study On Aggregation Of Particles/Gas At Polymer Interface

Polymer matrixes filled with nanoparticles can obtain a variety of novel materials with high performance. Dissolving gases into polymer is closely related to the polymer processing and gas separation process. In both of the two systems, which have the similar mechanism of interaction in some ways, there is a direct correlation between aggregation (and dispersion) of particles or gases molecules and polymer structures. Using similar theoretical methods, one can identify and separate the individual contribution of the different factors to the macroscopic behaviors at the micro-level, which is essential for designing and processing novel materials. In this paper, starting from the interaction between molecules (and groups), the evolution and formation of the microstructure in particle/polymer composites and gas/polymer systems are investigated and the interfacial properties of particles (and gas) aggregation are analyzed through constructing relevant theoretical models and combining quantum chemical calculations with molecular simulations. In this way, the correlations of molecular (and groups) interactions, microstructures and macroscopic properties can be determined. The main contents are summarized as follows:(1) The equilibrium and nonequilibrium behaviors of particles and polymer aggregating on a substrate are investigated. To characterize the contribution of polymer topology to the intrinsic free energy, a new free energy functional is constructed by combining the polymer reference interaction site model with density functional method. The effects of entropic and enthalpic interactions on the composite are evaluated by analyzing the equilibrium behaviors of particle and polymer depositing on the solid surface. Based on the dynamical density functional theory for colloidal particles including hydrodynamic interactions, a new dynamical density functional theory for nanoparticle/polymer/solution is constructed by introducing the free energy functionals of chain connectivity, conformation and the diffusion tensor. The validity of the approach is assessed by comparing with the Brownian dynamic simulations. The impacts of polymer conformation and hydrodynamics interaction are evaluated systematically by investigating the polymer-induced aggregation processes of particles near the substrate the velocities of polymer (flexible linear, semiflexible linear, flexible star, semiflexible star polymer) motions. It indicates that the nonequilibrium dynamics of particles show differential performances in different systems due to the effects of polymer conformation and hydrodynamic interactions.(2) To understand the microstructure of particle/copolymer composites, the microphase separation of diblock copolymer is investigated firstly. In the frame of confined polymer reference interaction site model integral equation, the free energy functional variation is inserted by constructing a novel bridge functional which fully considers the influence of confinement on polymer to improve the self-consistency. In this way, the theoretical model possesses the capability to describe the detailed structures accurately and to characterize the free energy quantitatively. The theoretical model is extended to investigate the microphase separation behavior of diblock copolymers at a solid surface and in bulk. The improved model is verified by comparing with the simulation data. The precise control of microstructures and interfacial properties can be achieved by adjusting the chemistries, conformation, density and the external environment (surface property). The extension of the integral equation offers an effective tool to predict microstructure of copolymers, and lays the foundation for the further study of particle/diblock copolymer composites.(3)Based on the basic characteristics of microphase separation in copolymers, the interfacial structures and properties of particle/diblock copolymer in ultrathin films confined between two planar surfaces are analyzed. The effects of particle size, particle-copolymer interaction, asymmetry of block sizes and the slit size are investigated. It indicated that the microphase separation of copolymer can direct the distribution of particles and the particle can act on the microdomain morphologies of block copolymer in reverse. The confinement has an effect on the ordering of diblock copolymers and the dispersion of particles. When keeping the lamellae with the similar thickness, the layer of particles near the substrates decreases with reduction in film thickness. The extent of this decrease becomes obvious with increasing the particle size.(4) Starting from the different interactions between CO2 molecule and the different groups of polyethyleneimine(PEI) oligomers and the correlations of the spatial structures, the structures of PEI and CO2 in bulk and at interfaces as well as the aggregation of CO2 are investigated by combining integral equation with quantum chemistry calculations. Incorporating with the experimental measurement, the effects of chain length and topology on the physisorption and chemisorption properties of PEI are investigated and the evaluations of the different contribution to total sorption from physisorption and chemisorption are performed. It indicates that the chain architecture has an effect on both physisorption and chemisorption. The structures and electrostatic density distributions of the compounds rearrange during the process of sorption and the variations are different due to the steric hinders and the electronic effect. The reactivities of different amine groups with different locations on one PEI chain are different. As the chain length increases, the capabilities of both physisorption and chemisorption decrease, but the influence on chemisorption becomes more obvious than on physisorption.