Modeling of polymer melt/nanoparticle composites and magneto-rheological fluids.

摘要

Polymers composed with carbon nanofibers, carbon nanotubes, and nanoclays show remarkable promise for enhancements of mechanical, electrical, and thermal properties of polymeric materials. This research work describes an experimental and modeling study of nanoparticle/polymer composite systems in their melt processing and performance phases. The goal is to create a predictive understanding of the coupling of processing to the development of the performance properties of the composite, focusing on the measuring and modeling of nano- and mesoscale features, and how they dictate macroscale behavior.; Nanostructurally-based constitutive models are developed to describe the comprehensive characterization of rheology, flow/particle interaction, and structure development of aqueous nanofiber suspensions and polymer nanocomposites. The aqueous nanofiber suspensions are modeled as elastic/rigid dumbbells suspended in a Newtonian solvent, where the bulk rheological properties are deduced from the microstructural measurements and all but one coefficients in the constitutive equations are specified not by a fit to macroscale experimental flow measurements, but rather in terms of primitive measurements of particle microstructure, carrier fluid viscosity and density, and temperature.; The rheological behavior of carbon nanofiber/polystyrene (CNF/PS) composites in their melt phase has been characterized as rigid rods in a viscoelastic fluid matrix: the nanofibers are described by rigid rod model and the modified Giesekus model is employed to describe the polymer behavior. The constitutive models, which include the strain-rate-dependent inter-fiber interaction parameter and polymer-fiber interaction parameter, successfully capture the transient and steady shear behavior of the CNF/PS composites and correctly predict the nanofiber orientations.; Based on the successes of microstructurally based models for CNF suspensions, kinetic theory-based models of MR fluids are developed by incorporating a magnetic force. The model characterizes the 3-D MR response of the composite system to mechanical and magnetic inputs in terms of primitive measurements of the carrier fluid and microstructural characterization of the metallic particles. This fundamental, 3-D, microstructurally based model will replace the inherent empiricism of the current modeling with a fundamental understanding of the mechanical and magnetic coupling in the fluid at the particle level.; All these models are validated through comparison of model predictions to experimental measurements of nano-/macro-scale behavior.