Free Energy and Surface Forces in polymer systems: Monte Carlo Simulation Studies

Sammanfattning: The thesis is focused on two major subjects: - Calculation of free energy is of great help in the study of any molecular system. The free energy determines phase behaviour of colloids and polymer solutions. It also controls the conformational properties of single macromolecules, e.g. DNA, proteins, copolymers. One of the most robust computer simulation techniques for free energy estimation is an Expanded Ensemble approach which is used throughout all the present work. Starting with a simple lattice polymer model, we develop and test an iterative procedure that makes the method automatic and accurate. Then we apply it to various polymer systems. The ideas behind a few similar approaches for overcoming rough free energy barriers lead to a non-equilibrium simulation method that yields e.g. the Gibbs free energy profile, G(V)=F(V)+pV. The latter is a direct route to phase diagrams which are invaluable when studying a thermodynamic system. This way we investigate the phase behaviour of constrained polymer systems. - Surface force calculation: another application of the expanded ensemble is to equalize the chemical potential of a polymer solution confined to a planar pore while changing its width. Forces acting along and perpendicular to the surfaces are then obtained by usual means of statistical mechanics and from the thermodynamic relations, the surface free energy in particular. A number of different polymer systems were dealt with in this framework.