Title: Electrokinetic effects in hindered transport
Description: Macromolecular solutes in liquid-filled pores of molecular dimensions have reduced diffusivities and are sieved during filtration. The objective of this thesis research was to re-examine several aspects of hindered transport theory, particularly the effects of electrical charge. The theory for hindered diffusion and convection of a neutral spherical particle in a pore was first reviewed and extended. Using recent off-axis hydrodynamic results from the literature, new hindrance factor expressions were derived which eliminate the need for "centerline approximations". Root-mean-square errors in such approximations were found to be 20% and 6% for diffusive and convective hindrance factors in cylindrical pores; for slit pores the errors are 16% and 10%. The effects of solute and pore charge on hindered diffusion and convection were then investigated. With particle and/or fluid motion, the counterions in the double layers cannot maintain their equilibrium distributions, creating an electrical force on the particle and altering the viscous and pressure forces. Both the enhanced drag and the lag coefficient may be affected, which had not been appreciated previously. These "electrokinetic" effects were examined for a sphere in a cylindrical tube, the surfaces being of like charge and constant charge density. A perturbation scheme involving both the electrolyte Peclet number and the surface charge density was employed, along with finite element calculations.

t was found that electrokinetic retardation can noticeably decrease the intrapore diffusivity of a charged macromolecule, relative to that for an uncharged system. The increase in the drag is much greater for confined particles than for ones in bulk solution. However, the electrostatic decrease in the equilibrium partition coefficient was a more important determinant of the overall diffusional permeability. In analyzing charge effects in hindered convection, the linearity of the governing equations permitted the effect of the double layer polarization to be separated from that of the streaming potential. The relaxation effect decreases the lag coefficient, while the streaming potential increases it. The charge effect can alter the intrapore convective hindrance factor significantly. However, in terms of transmembrane convective fluxes, the electrostatic decrease in the equilibrium partition coefficient again outweighed the electrokinetic effects.