| Interfaces and their interactions are important for biological and non-biological applications. For example, the interactions between the protein and water or the nanofiller and polymer matrix govern the solvation, miscibility, and ultimately affect macroscopic properties, such as a protein binding to a ligand, the wettability of a surface, or mechanical properties of a nanocomposite. Here we study both aqueous and non-aqueous systems to understand the thermodynamic, structural, and dynamic aspects of solvation in bulk and interfacial systems of interest to nano and biotechnologies.;Specifically, we study the solute lengthscale dependent solvation in n-octane liquid. We are interested in n-octane as a model organic liquid/oligomer, with an eye toward understanding nanoparticle solvation and coupling in polymers. In water, the solvation of hydrophobic solutes is known to be lengthscale dependent, with thermodynamic as well as structural aspects of solvation evolving as the solute size increases. Such behavior arises from the fact that solvation of small and large solutes is governed by different physics -- small solutes are accommodated in the fluctuating bulk solvent, whereas, large solutes require the formation of an interface. Our studies of solvation in n-octane using indirect umbrella sampling (INDUS) bring out lengthscale dependent solvation in this liquid that is qualitatively similar to that in water. We also study solvation in n-octane at interfaces, specifically near a graphene surface with scaled attractions with n-octane to gain insights into solute-solvent coupling, interfacial solvation, and density fluctuations in non-aqueous solutions.;We also study other interfacial systems that are biologically relevant. For example, we studied lysozyme near a carbon nanotube (CNT) surface. Our simulations highlight the importance of arginine residues on the protein surface in mediating protein-CNT interactions. We confirm the unique role of arginine by studying the individual components of arginine: the guanidinium group and the remaining moiety (norvaline). We show that the dominant contribution in arginine binding comes from the guanidinium group.;As part of ongoing and future work, we present applications of the INDUS method to study the protein surface hydrophobicity of human gamma-D crystallin, a structural protein in the eye lens, and its P23T variant with a single point mutation from proline23 to threonine. The P23T variant has been implicated in self-aggregation leading to the formation of cataracts. Finally, we also present results on solvation of self-assembled monolayers of immobilized ionic head groups near hydrophobic head groups, which are of theoretical and practical/experimental interest. |
