Molecular Modeling of Tethered Polyelectrolytes

Owen Hehmeyer, Princeton University

Molecular simulation is a valuable tool for accessing structural and thermodynamic information in systems where experiments are difficult to perform or where analytical theories are inadequate. End-tethered polyelectrolytes are such a system. Analytical theories are limited because of the long-range nature of electrostatic interactions. Physical inaccessibility limits experiments. Molecular Dynamics (MD) simulation, Monte Carlo (MC) simulation, and Mean Field (MF) theory were used to study tethered polyelectrolytes in confined geometries.

Parallel MD simulations were used to examine a model system that approximates a flexible polyelectrolyte, such as sodium polystyrene sulfonate, grafted to two apposing walls [1]. The effect of the polymer grafting density, chain length, and gap width on the structure and pressure was examined. Results are compared to surface forces apparatus studies of similar systems.

The structure of tethered polyelectrolytes on a single wall was studied using MC and single-chain MF theory [2]. The density profiles of the monomers and counterions and the brush height were investigated as a function of grafting density, chain length, and charge density.

The behavior of a tethered polymer brush with a single charge at the polymer free-ends was examined as a function of grafting density, chain length, temperature, and surface charge using MC simulation. Surface charge was found to effect a substantial change in brush height.

Comparisons of the relative efficiencies and limitations of MD, MC, and MF are made, as well as comparisons to experiment.

[1] O. J. Hehmeyer and M. Stevens, “Molecular Dynamics simulations of grafted polyelectrolytes on two apposing walls,” J. Chem. Phys., 122, Art. No. 134909, 2005.

[2] O. J. Hehmeyer, G. Arya, I. Szleifer, and A. Z. Panagiotopoulos, “Monte Carlo Simulation and Mean-Field Theory of Tethered Polyelectrolytes,” (in preparation).

Abstract Author(s): Owen Hehmeyer and Athanassios Panagiotopoulos<br />Princeton University