Surface Forces Mediated by Charged Polymers:  Effects of Intrinsic Chain Stiffness

Abstract

The strength and range of surface forces in a system consisting of charged polymers with variable intramolecular stiffness confined between two charged planar surfaces have been investigated by Monte Carlo simulations. The negatively charged surfaces are neutralized by polymers carrying charges of opposite sign. Introducing the intermediate intrinsic stiffness of the chains gives rise to a weaker, but more long-ranged attraction between the surfaces. In the limit of infinitely stiff chains, this bridging attraction is lost, but it is replaced by a strong correlation attraction at short distances. Comparisons with predictions by a correlation-corrected polyelectrolyte Poisson-Boltzmann theory are made. The theory predicts surface attractions that are somewhat too weak, but all qualitative features are correctly reproduced. Given the crudeness of the model, the quantitative agreement is satisfactory.

Block polyelectrolytes and colloidal stability

“…These effects are also directly related to adsorption characteristics, but not in the way these influence bridging, i.e., a stronger adsorption generates a more extensive charge reversal at large separations. In agreement with earlier work [2,9], the separation at which the surfaces become overcharged agrees well with the free energy barrier maximum (not shown). Still, strictly speaking, overcharging does occur at slightly shorter separations.…”

“…when the total polyion charge exactly matches the total colloid charge [3][4][5][6]. This is in qualitative agreement with collective findings from a considerable amount of simulation work [7][8][9].…”

“…Let us first discuss the adhesive minimum at short separations; 20-30 Å. This is primarily generated by attractive bridging interactions [7][8][9][23][24][25][26][27]. We note that the adhesive minimum becomes stronger and more short-ranged if we:…”

Polyelectrolyte Adsorption on Solid Surfaces: Theoretical Predictions and Experimental Measurements

“…where n b in our case is the bulk concentration of charged beads, which in the models of this study are always identical to the bulk monomer concentration 1 . A natural extension of the theory would be to allow λ to vary in space.…”

“…This has important implications to the interactions between charged particles, or surfaces, in solution. [1][2][3][4][5] The overcharging generates an electric double layer free energy barrier at long range, while bridging and ion correlations mediate a strong attraction at short separations. The free energy barrier can be reduced, or eliminated, by the addition of simple salt.…”