Structure of weakly charged polyelectrolytes at a solid-liquid interface

(Received 25 January 1993, accepted in final form 26 March 1993)

Abstract
The equilibrium structure of a monolayer formed by long polyelectrolyte chains adsorbed at the interface between a charged surface and a dilute polyelectrolyte solution is analysed. The self-consistent field equations for the configurational probability of the chain are solved numerically for different parameter values of the system including the surface and polymer charge density, the amount of adsorption and the Debye-Hückel screening length. The effect of intramolecular long range Coulombic forces on the segment density profile is examined. By coupling the numerical results with simple thermodynamic arguments, we reach exact analytical expressions for the layer thickness and define critical adsorption conditions. In general, polyelectrolytes are adsorbed into flat layers. However, under conditions of weak electrostatic screening and low surface and polymer charge densities, we expect large loops to be formed. Strong electrostatic screening does not lead to expanded conformations but causes chains to desorb.