(192aj) Influence of Solvent on the Thermodynamics of Molecular Adsorption on Metal Surfaces

Solid-liquid interfaces are central to the functional aspects of various applications, including the synthesis of nanomaterials and heterogeneous catalysis. In many applications that feature the binding of certain molecular species to a solid surface, the solvent can also play a key role. We investigate the influence of ethylene glycol solvent on the adsorption of polyvinylpyrrolidone (PVP) analog molecules on Ag surfaces by comparing systems in vacuum to solvated systems. Ethylene glycol and PVP are commonly present in the solution environment of Ag nanocrystal syntheses, in which the nanocrystal morphology is directly influenced by the choice of solvent and adsorbate. We calculate the potential of mean force between PVP analog molecules and surfaces of Ag using molecular dynamics simulations based on a many-body organic-metal force field. From our potential-of-mean-force calculations, we observe that the binding free energies of the PVP molecules are drastically smaller in the presence of solvent because these molecules are stabilized by solvent in the bulk solution environment. The observed entropy changes due to adsorption are negative in vacuum but they are zero or slightly positive in solvent. Our results demonstrate that the liberation of adsorbed solvent molecules when a molecule binds to a solid surface can contribute more to the system's entropy change than the configurational entropy loss due to molecular adsorption. We find the inclusion of solvent molecules to be a critical feature in correctly modelling molecular adsorption in solution.