Molecular modeling of confined polymers

Molecular Dynamics (MD) simulation, Monte Carlo (MC) simulation, and Mean Field (MF) theory were used to study the structure and thermodynamics of polymers in confined geometries. 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 and polymers confined in a slit geometry are two such difficult systems. Analytical theories are limited because of the long-range nature of electrostatic interactions. Physical inaccessibility limits experiments.; The effect of confinement on the phase behavior of lattice homopolymers was studied using grand canonical MC simulations in conjunction with multihistogram reweighting. The scaling of critical parameters and chain dimensions with chain length was determined for lattice homopolymers in strictly two dimensional and slab geometries, and compared to the bulk results. The influence of confinement on critical behavior persists even in a thick slab due to the diverging correlation length of density fluctuations.; MD simulations were used to examine a model system that approximates a flexible polyelectrolyte, such as sodium polystyrene sulfonate, grafted to two apposing walls. The effect of the polymer grafting density, chain length, and gap width on the structure and pressure was examined. The apposing brushes seek to avoid interpenetration as the gap between the walls narrows. The avoidance of interpenetration may be the origin of lubrication in tethered polyelectrolyte systems.; The structure of tethered polyelectrolytes on a single wall was studied using MC and single-chain MF theory. The monomer and counterion density profiles and the brush height were investigated as a function of grafting density, chain length, and charge strength. It was found that MF theory that incorporates counterion condensation agrees well with MC results. Grafting density is found to have only a mild effect on brush height.; Grafted polymers carrying a single charge at the free-ends were studied with MC simulation. The brush height was found to change substantially with the surface charge density. The interaction of the same brush with adsorbing protein was examined with MC and MF. It was found that the brush hinders protein adsorption.