Dynamic simulations of suspensions of rod-like polymers and colloids

Simulations presented in this dissertation advance knowledge of the dynamics of suspensions of rigid and semi-rigid Brownian fibers. This work resolves competing claims concerning the power-law scaling for the concentration dependence of the rotational diffusivities. The power-law scaling states that the rotational diffusivity DR scales as DR/ DR0 ∼ (nL3)nu, where DR0 is the rotational diffusivity of a single fiber in infinite dilution, n is the number density (number of fibers per unit volume), and L is the fiber length. The choice of hydrodynamic model, with an intrinsic ratio of the rotational to translational diffusivities at infinite dilution L2DR0/DT0 , sets the value of the exponent nu in the scaling. The aspect ratio of the fibers also affects the scalings, with strong variations for ratios less than fifty; ratios of fifty or higher can considered infinitely thin. An analysis of the numerical integration method was performed, resulting in a new algorithm with less error and higher efficiency.; Adding flexibility delays the number density at which fibers become significantly hindered by their neighbors and enter the regime where a strong decrease in the rotational diffusivity occurs. Once within this semi-dilute regime, the power-law scalings of the semi-rigid fibers closely match those of rigid fibers with corresponding hydrodynamic models and aspect ratios. Comparing simulations of rigid and semi-rigid fibers to experimental results demonstrates that different micro-mechanical models can produce results which are indistinguishable within measurement capabilities. Consequently, proper models cannot be distinguished based solely on their rotational diffusivities, so other measures are needed to identify the appropriate model.; Including hydrodynamic interactions into the simulations will provide further insights into the dynamics of fiber suspensions. Investigations of a parallel computation of the pair interactions and Cholesky decomposition indicate that simulating systems of over one hundred fibers is feasible.