Integral Equation Theory Study On Microscopic Structure And Properties Of Polymer Materials

Integral equation theory (IET) has been employed recently to study the structure and thermodynamics properties of polymer systems. It is a very attractive field in physics, polymer science and chemical engineering. In this work, the polymer reference interaction site model theory (PRISM) is used to investigate the structure and thermodynamics properties in polymer and polymer nanocomposites, which is the first time in China to use integral equation theory to study the polymer systems. The main results obtained are:The PRISM theory is introduced in detail. Different kinds of computationally convenient methods for determining the intramolecular structure factors are discussed and evaluated extensively, together with the usual closure approximations used in PRISM theory. The two numerical methods to solve PRISM integral equations are introduced based on the Discrete Fourier Transformation and Fast Fourier Transformation. Combining PRISM theory, MD simulation and Variational method, a single-site semi flexible model is proposed to describe atactic polystyrene (aPS) melt. This is a reasonable method to investigate real polymer systems. The semiflexible model can capture the main features of aPS, and can semi-quantitatively describe the intermolecular correlation function, intramolecular correlation function, solubility parameters and x-ray scattering intensity for real aPS melt. Good agreement between theory and MD simulation is obtained.An eight-site model is proposed to further describe aPS melt, where the intramolecular structure factors needed in PRISM calculations are obtained from MD simulations. The PRISM theory successfully predicts various microscopic information such as correlation functions and structure factors, and macroscopic properties such as solubility parameters and x-ray scattering intensity of real aPS melt. Quantitative agreements among theory, MD simulation and experiments are obtained.The PRISM theory is used to study chain polymer nanocomposite melts. The theory is reliable to describe the structure and effective interactions in chain polymer nanocomposite melts which agree quantitatively with the MD simulations. Then the PRISM theory is firstly employed to predict the properties of the polymer nanocomposites where the particle volume fractions are nonzero. The roles of the particle volume fraction, degree of polymerization, and nanoparticle-monomer size ratio are systematically investigated.The PRISM theory is used to study the structure and effective interactions in star polymer nanocomposite melts. The influences of thenanoparticle-monomer attraction strength, particle volume fraction, arm number, arm length, and nanoparticle-monomer size ratio are systematically studied. Two types of aggregation are observed in star polymer nanocomposite melts: the contact aggregation and the bridging aggregation. The different stable states of organization between nanoparticles are extensively discussed according to the interplay between the star architecture and the nanoparticle-monomer attractive interactions.