Thermodynamics and Structure of Polymers in Confinement

Owen Hehmeyer, Princeton University

The structure and thermodynamics of several model polymer systems in confinement were studied using computer simulation.

The effect of confinement on the phase behavior of lattice homopolymers with short-range interactions was studied using Grand Canonical Monte Carlo simulations in conjunction with multihistogram reweighting. The scaling of critical parameters and chain dimensions with chain length was determined in both strictly 2D and slab geometries. The inverse critical temperature was found to scale linearly with the Shultz-Flory parameter for slab geometries, as it does for the bulk system. The critical volume fraction scales as a power law for all systems. The influence of confinement on critical behavior persists even in a thick slab due to the diverging correlation length of density fluctuations. The scaling of the radius of gyration with chain length in the slab system increasingly resembles the scaling in the strictly 2D system as the chain length increases.

Uncharged, tethered, lattice homopolymers were studied theoretically using a mean-field theory and were simulated using Monte Carlo. The density profile of the polymer brush was found for a variety of densities. Comparison of the two methods shows that mean-field theories can be successful describing the structural behavior of tethered polymer systems. The structure of charged, tethered, lattice polymers were studied using Monte Carlo. Structure was investigated as a function of grafting density, charged bead location, and salinity. Efforts continue to use mean-field theories to describe the behavior of charged, tethered systems.

Initial practicum efforts for using molecular dynamics simulations to study tethered, biological polyelectrolyte systems after the methods of Crozier and Stevens are presented. The Large-scale Atomic/Molecular Massively Parallel Simulator was used complete initial studies. The effect of the surface density of the grafted polymer and the effect of salinity on the structure of the polymer brush are being studied. 

Abstract Author(s): Owen Hehmeyer