Molecular Insights on the Boundary Behavior of Liquids

Abstract

The last part of my thesis concerns the translational diffusion of molecularly thin polymer melt. While simulations have been performed, to my knowledge no direct measurements exist yet of polymer melt diffusion in molecularly-thin films. This is due to the lack of proper experimental tools and the large number of variables involved. In this work, a new experimental platform was developed by combining the surface forces apparatus with a fluorescent technique called the fluorescence recovery after photobleaching to shed light onto the molecular origin of the unique dynamics of a confined polymer melt. The effects of two very fundamental factors, namely the thickness dependence and the pressure dependence on the centre-of-mass diffusion of the confined polymer melt have been investigated. A strong pressure dependence within a highly confined melt suggests that the dynamics within the molecular thin melt are highly heterogeneous. On the other hand, a weak thickness dependence and also viscosity dependence suggest that the dynamics of the confined polymer melt is governed by the polymer-surface interaction, with the degree of confinement and the viscosity of the solvent playing less important roles.