(500a) Transient Shear and Extensional Rheology and Nanostructure of Polymer Nanocomposites

There has been much interest in carbon nanofiber (CNF) based polymer nanocomposites in recent years because of the potential to create materials with enhanced mechanical, thermal, and electrical properties while using much lower particle loadings than microscale fillers such as carbon black, carbon fibers, and glass fibers. The mechanical, thermal, and electrical performance properties of the nanocomposite are greatly dependent upon the nanoparticle orientation developed during processing and the dispersion of the particles within the polymer matrix. Thus it is desirable to be able to model and predict the evolution of particle orientation during processing. Accurate models provide the predictive capability necessary to design manufacturing processes that optimize the desired performance properties.

We have studied the rheological behavior of melt phase polystyrene/carbon nanofiber composites under transient shear and extensional flows. A constitutive model has been developed that predicts the rheology and nanostructure development with time during these two different types of flow. The model includes parameters that account for properties of the composite such as the rheology of the polymer matrix, nanoparticle shape, nanoparticle concentration, particle-particle interactions and polymer-particle interactions. To improve the model's predictions we have developed a method to experimentally measure the 3-dimensional structure of the nanofibers. Our nanostructure measurement technique allows us for the first time to be able to validate 3-D model predictions through comparison with 3-D experimental measurements.