Equilibrium structure in polymer-coated colloids

A theory for the coupled translational and conformational equilibrium in colloidal suspensions stabilized by coatings of charged or neutral polymers is presented. The theory combines a Monte Carlo calculation of an ideal chain in a mean field of its neighbors with Ornstein-Zernike integral equations that describe the electric double layer and inter-colloid correlations, and gives the local monomer densities, counter-ion distributions, and center-of-mass pair correlation functions, as well as concomitant structure and form factors and thermodynamic functions. It is shown that (1) the polymer chains can simultaneously exhibit crystalline, flexible-rod, and disordered regions, depending on the distance from the colloid surface, charge, and extent of screening; (2) local electro-neutrality is obeyed down to scales of roughly a Debye length; (3) there is very little inter-penetration of the polymer layers, even for neutral polymer chains in moderately good solvents. Finally, continuum descriptions of the polymer are presented and solved.