Modeling the Behavior of Macromolecules at Interfaces

The behavior of macromolecules at an interface is often remarkably different from  their behavior in the bulk. Understanding this behavior, and the physicochemical  processes that govern it, is the key to designing better polymers, surfactants and proteins. However, there are many interfacial phenomenon that occur in macromolecular materials which classical thermodynamics and macroscopic fluid mechanics can notadequately describe. In this thesis, we employ theory and computationtounder stand the behavior of macromolecules at interfaces.  

We first investigate the mechanisms which govern oxygen transport in ionic polymers, in an effort to identify modifications to the polymer chemistry which could reduce oxygen transport resistance. Using molecular simulations, we model the transport of oxygen in a polymer that is representative of commercial offerings, and in a  recently developed high oxygen permeability polymer. We quantify the rate of oxygen transport, and present evidence that the chemical and morphological differences  between the two polymers affect oxygen transport properties. Specifically, we find  that the high oxygen permeability polymer exhibits improved oxygen solubility, but  diminished oxygen diffusivity.  

We use these results to guide further analysis, which investigates the specific effects that morphology has on the kinetics of oxygen transport. We use computational  geometry and data science techniques to describe morphological characteristics, finding that the size and continuity of hydrophilic domains has a strong impact on oxygen diffusivity. We then make direct comparisons between oxygen diffusivity and the local chemical environment of oxygen molecules.  

Finally, we develop and discuss models of the electric double layer in a solution  which contains ionic surfactants. We identify key differences in electric double layer  structure predicted using analytical techniques and molecular dynamics simulations,  and use these results to determine how differences in the structure of the electric double layer will affect diffusiophoretic mobility.