Molecular dynamics simulations of nanoscale interfaces: From simple liquids to biological systems

Nanoparticles have great potential in various fields, such as drug delivery, electronics, and energy. Due to their high surface area to volume ratio, the physical properties of nanoparticles often vary with their size, unlike the corresponding bulk material properties which are only related to the material composition. One size dependent property is surface tension, which governs the behavior of nanoparticles in a liquid and has great implications for adhesion, wetting, and particle self assembly. Unfortunately, current experimental determination of surface tension at the nanoscale relies on Young's theory which may yield erroneous results. Moreover, there are conflicting experimental data on the potential impact of nanoparticles toward the environment and human health. Here, we used molecular dynamics simulations to probe nanoparticle/liquid surface tension and to study the interaction of nanoparticles with biological membranes.;We developed a novel method of measuring solid/liquid surface tension at the nanoscale by applying a mean field treatment to a spherical nanoparticle. In addition, we observed a hydrophobic to hydrophilic transition with nanoparticle size which motivated us to propose a novel colloid self-assembly mechanism. We also studied the behavior of a nanoparticle at a liquid/liquid interface and compared our results to Young's theory. Moreover, we illustrated the importance of assigning the Gibbs dividing surface toward the interpretation of the three phase line tension. The results presented may be helpful for future theoretical and experimental analysis of nanoscale interfaces.;To study the effect of carbon-based nanoparticles on biological membranes, we derived coarse grained (CG) parameters for fullerene molecules compatible with an existing CG model for biomolecules. From our simulations of fullerene doped lipid monolayers, we found fullerene molecules may enter into the body through the lipid monolayer to bilayer transition at the lung alveoli surface during the respiration cycle. In addition, we observed a strong perturbation of the lipid monolayer to bilayer transition due to the presence of larger sized fullerenes. The results have potential implications on the toxicity of fullerenes towards lung tissue.