Reverse Non-Equilibrium Molecular Dynamics Simulations of Thermal Transport through Functionalized Gold Interfaces

In this dissertation, I present work in performing reverse non-equilibrium molecular dynamics simulations of heat transfer through complex metal/ligand/solvent interfaces. More specifically, I characterize heat transfer through gold interfaces that are functionalized with anti-aggregation agents. The effects of gold facet, curvature, size, polarizability, and ligand identity and density on the interfacial thermal conductance are examined. I also explore the effects of ligand choice on the solvent thermal conductivity. Simulations of solvated gold functionalized with sodium citrate are explored in Chapter 2. The binding preferences of citrate were found to depend on gold curvature more than polarizability. The solvent conductivity was determined to be water-dominated, as the conductivity in citrate-containing systems was nearly identical to those of pristine gold solvated in water. Interestingly, the dependence of conductance on polarizability was found to vary depending on the morphology of the particle. In Chapter 3, the ligand of interest was a low molecular weight thiolated polyethylene glycol (PEG). There was a significant increase in conductance compared to the citrate-capped interfaces, indicating that strong metal-to-ligand and ligand-to-solvent coupling are likely responsible. Chapter 4 examines thermal transport through interfaces functionalized with cetyl trimethylammonium bromide (CTAB) or (16-mercaptohexadecyl) trimethylammonium bromide (MTAB). The link between increased conductance and strong ligand-involved coupling was further observed, as the CTAB-capped systems had lower conductance values than any other system. With only strong metal-to-ligand coupling available in the MTAB systems, the conductance here was higher than in CTAB systems. Finally, Chapter 5 details simulation studies for a different project in collaboration with experimental researchers. The binding behaviors of different PFAS molecules on a graphene surface were investigated. The five molecules (Tf, PFES, PFBS, PFHxS, and PFOS) were found to bind to graphene in different fractions via their oxygen and fluorine atoms, as well as their centers of mass.