A multiscale model for polymer nanocomposites

A multiscale material model for linear amorphous polymer composites containing spherical nanometer sized filler particles is presented. The multiscale model has three main components. The first component is a molecular scale model or discrete model of the material system that uses a coarse grained representation for polymer chains and a generic representation of filler particles to simulate the chain structure and dynamics. Two types of information are obtained from the discrete model and used in the larger scale model. The first is an understanding of the physics of the chains in the neighborhood of filler particles. This understanding is used to guide the conceptual structure of the larger scale model. The second type of information gained from the discrete model is the specific quantitative parameters that are required as inputs to the larger scale model. The second component is the larger scale mesoscopic rheological model based on the molecular theory of the viscoelasticity of linear polymer liquids and adapted for the fractionally diffusive nature of polymer chains in a nanocomposite. The third component of the multiscale model applies to the continuum scale and is a finite element implementation of the mesoscopic rheological model.{09}This thesis presents all three components of this model with particular emphasis on the first and third components. The understanding of the physics of polymer nanocomposites from the discrete scale model include the structure and dynamics of polymer nanocomposites as a function of the wall to wall distance between filler particles (determines the volume fraction of filler particles) and the interaction energy between monomers and particles. It is found that the chain dynamics is slowed by both increasing filler volume fraction and increasing monomer-particle energetic interaction. The average attachment time of a chain to filler particle is found to be an exponentially increasing function of the monomer-particle energetic interactions. The mesoscopic rheological model is generalized for three dimensional complex stress states and implemented as a user material subroutine in the commercial finite element analysis package ABAQUS/Explicit. A boundary value problem using the finite element method and material model is solved and results presented.