Hydrodynamics, rheology and conduction in suspensions of arbitrarily shaped fibers

Hydrodynamic and transport properties of fiber suspensions are affected by fiber characteristics and processing conditions. In this thesis we develop simulation methods to predict the dynamics of single fibers in laminar flows, as well as the rheology and conductivity of fiber suspensions. Quiescent settling and shear flow simulations employ an offset bead-shell method for the calculation of the grand hydrodynamic resistance matrix of rigid isolated fibers of arbitrary shapes. The offset bead-shell method reproduces various analytical and experimental hydrodynamic results. We present experimental measurements of the settling dynamics of asymmetric fibers which are in quantitative agreement with the simulations. Skew fibers with a gravity torque settle following a helical trajectory. We show that separations by shape are possible based on differences in the horizontal component of the terminal velocity and angular velocity. Simulations of fibers in shear flow show that the intrinsic viscosity is larger for fiber shapes that depart from the straight shape. Shape measures based on invariants of the translational friction tensor correlate better with intrinsic viscosity than other shape measures, including the curl and kink indices. A master curve is presented that relates the intrinsic viscosity and the shape measure based on the translational friction tensor. Simulations based on three free-draining methods are in qualitative agreement with those based on the offset bead-shell method, with better agreement for fibers of larger aspect ratio. The conductivities of sheared suspensions of interacting flexible fibers, as well as suspensions with randomly oriented rigid fibers were calculated via fiber-level simulations. Systems with ohmic conduction are modeled via a bead-chain method based on the multipole expansion method of Bonnecaze and Brady, which reproduces results reported in the literature for the conductivity of dilute suspensions. Systems whose conduction is dominated by tunneling are modeled via a resistor network method. Percolation thresholds of moderately sheared suspensions of helical fibers are significantly lower than those of randomly oriented rods of the same aspect ratio. Factors that enhance the conductivity of suspensions are large tunneling lengths, low shear rates and shapes that depart the most from the straight shape.