Eric S. G. Shaqfeh, Stanford University, 381 North South Mall, Stanford, CA 94305 and Brendan Hoffman, Chemical Engineering, Stanford University, 381 North South Mall, Stanford, CA 94305.
Many dispersions of colloidal particles with application in materials processing, biological assays, or medicine, contain elongated or rod-like particles. In microfluidics applications, these suspensions are often subjected to electric fields, and therefore, even if they are neutral, polarization creates qualitatively new flow phenomena. Much recent literature has demonstrated that the dynamics of these suspensions at non-dilute concentrations involves physical principles which are unlike those operating in suspensions of spheres. In this work, we examine, via numerical simulation, three problems which exemplify these differences. First, we examine the effect of rotational Brownian motion on the stability and wavenumber selection of sedimenting fiber suspensions. Note in this context, that the instability in sedimenting rod like particles is associated with the particle orientation evolution and therefore, Brownian motion can have a qualitative effect on the instability in finite vessels. Next, we then describe the dynamics of dilute suspensions of polarizable, Brownian particles in electric fields, with specific comparison to the experiments on 'nano-barcodes' by Rose and Santiago. This work extends the initial simulations of Saintillan et al. 2007 to direct comparison to new experimental data. Finally, we examine the microchannel flow of dilute and semi-dilute Brownian rodlike solutions to understand the effects of particle anisotropy on shear induced migration and suspension microstructure with and without applied electric field.