(260d) Effect of Solvent on the Binding Energies of Molecules on Metal Surfaces

The adsorption of molecules on surfaces in a liquid environment is an important phenomena in many cutting-edge applications such as nanomaterials, biosensors, and catalysis. Although the interaction between molecules and surfaces has been extensively studied in the past, the solvent's influence on the adsorption thermodynamics has not yet been fully understood. Here, we examine the adsorption of polyvinylpyrrolidone (PVP) on Ag surfaces in both ethylene glycol solvent and in vacuum, for comparison. This interface is commonly present in the shape-selective synthesis of Ag nanocrystals, in which the choice of solvent and adsorbate directly influences nanocrystal morphology. We use molecular dynamics simulations based on a many-body organic-metal force field to calculate the potential of mean force between PVP analog molecules and surfaces of Ag. In the resulting binding free energies, we see that solvent drastically decreases the binding free energy of the molecules because the solvent stabilizes the molecule in the bulk solution environment. We find that the system's entropy changes due to adsorption are generally negative in vacuum but zero or slightly positive in solvent. These results show that the liberation of adsorbed solvent molecules when a ligand binds to a solid surface can contribute more to the system's entropy change than the configurational entropy loss of the ligand due to adsorption. Our study underscores the importance of including solvent in theoretical models for molecular adsorption.