(332a) Rheological Measurements And Modeling Of Carbon-Filled Liquid Crystal Polymer Composites

In this poster we will present results on the rheological testing of carbon-filled liquid crystal polymer. The application of this research is to use these materials for fuel cell bipolar plates.

In this project, the liquid crystal polymer is Vectra, the carbon fillers are Ketjenblack carbon black, Thermocarb synthetic graphite, Fortafil carbon fiber, or Panex carbon fiber. There are varying filler volume fractions for each single filler material.

Over the range of shear rates tested using a capillary rheometer, the composite was shown to exhibit power law behavior, where the viscosity η is dependent upon the shear rate γ according to the relationship η = m γ ^n-1. For pure Vectra, we measured m =690 Pa-s^0.54 and n = 0.54. As the filler was added, there was an increase in the value of m for all filler types and a decrease in the value of n for Ketjenblack, Thermocarb, and Fortafil.

Furthermore, numerical finite element computations were performed using COMSOL Multiphysics software. Using the power law parameters calculated from the experiments, the numerical results showed a rapid velocity profile development and the pressure drop matched that seen in the experiments when using no-slip boundary conditions. In fact, the finite element model pressure drop results for different L/D capillaries pass through the origin, signifying no significant loss of pressure at the inlet to the capillary due to rearrangement of the velocity profile and the presence of elongational flow. This is the expected result for the power law generalized Newtonian fluid constitutive model.

Such work is a necessary first step in developing 2D or 3D mold filling simulations for fuel cell bipolar plate applications.