Conformation of surface bound polyelectrolytes: I. Implications for cell electrophoresis

We present a self-consistent calculation for a layer of short-chain polyelectrolytes grafted to a planar interface. Individual self-avoiding chain configurations are generated on a tetrahedral lattice. By evaluating the complete ensemble of configurations in the presence of a self-consistent field we determine averages for the equilibrium layer height, segment and charge density profiles. These describe the response of the layer to changes in the surrounding medium, in particular to electrolyte concentration. This self-consistent model of a biological cell, which is known to have an extended layer of charge exterior to the membrane bilayer surface, is applied to the problem of cell electrophoretic mobility. We compare the electrophoretic mobility deduced from the application of this model with that for a constant profile of charge and segments and with the case of a constant segment profile with a plane of charge, usually assumed in the literature. We find that, within the region of concentrations studied here and with the chain lengths used, there is general agreement between the different descriptions.