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Given the potential of Titanium Dioxide in diverse areas including alternative energy, drug delivery and protein adsorption, it is imperative that the underlying mechanism of surface-water interactions be thoroughly understood. Interaction lifetimes between the surface and the surface-adjacent water molecules have a major bearing on interfacial behaviour. Our study employs Molecular Dynamics simulations to understand interfacial interactions of water with a Titanium Dioxide surface, with focus on these interfacial interaction lifetimes. Two polymorphs of Titanium Dioxide, Anatase (101) and Rutile (110) are studied.

Molecular dynamics and Monte Carlo simulation studies were carried out to investigate adsorption behavior of carbon dioxide and methane mixtures on illitic clay surfaces under dry conditions. Various compositions of the mixtures and distributions of isomorphic substitutions in clay layers were chosen to explore competitive adsorption depending on component concentration and charge localization. The simulations show that carbon dioxide is preferentially sorbed on the illitic surface and is capable to promote methane desorption. Density distributions of the molecular species in pore space reveal formation of multilayers on the clay surfaces at elevated pressures. Mixed adsorption isotherms were compared with adsorption isotherms of pure compounds and thermodynamic quantities were reported to characterize the interaction of the carbon dioxide and methane with the clay surface.

Carbon dioxide and methane interaction with organic matter mostly represented by kerogen heavily impacts carbon storage and enhanced gas recovery in shales. Kerogen pores are dominated by micropore network connecting mesopores and understanding adsorption in kerogen is a key element for estimation of shale capacity to retain and release fluids. In this work, molecular dynamics and Monte Carlo simulations were engaged to study adsorption of carbon dioxide, methane, and water in immature type II-A kerogen. Fluid adsorption induces volumetric swelling and pore space expansion with water imposing the largest impact compared to carbon dioxide and methane. The adsorption isotherms show that water demonstrates the highest uptake (up to 6.2 mmol/g) which is attributed to strong water-kerogen energy interaction and the tendency to form large water clusters. On the other hand, methane and carbon dioxide show similar adsorption (up to 1.5 mmol/g) in the micropore space of kerogen. The analysis of cluster size distributions implies a large extent of a disconnectivity in micropores with adsorbed carbon dixoide and methane, while micropores demonstrate continuity with adsorbed water.

Self-assembly of biocompatible nanoparticles is part of a promising field in drug delivery and biomaterials. Virus capsids are an example of nanoparticles capable of being tethered with functional groups for specific targeting. There have been experimental efforts on grafting polymers to virus capsids to synthesize tailored nanostructures. To provide insight at the nanoscale, we perform a highly coarse-grained molecular dynamics study, simulating the self-aggregation of cowpea mosaic virus (CPMV) capsids decorated with polyethylene glycol (PEG) and PEG polylactic acid (PLA) block polymers. We examined the effects of grafting architecture and volume fraction on equilibrated clusters. Characterization of the aggregation dynamics are summarized by the radius of gyration of the clusters, coordination number distributions, and average cluster size. When the system and methods are parameterized with respect to atomistic models or empirical results, the results can serve as the basis in broadly mapping the theoretical design space for controlled self-assembly of polymer-decorated virus capsids.

Titanium dioxide based catalysts, such as Pt/TiO 2 , have shown promise as water splitting photocatalysts and have been extensively studied experimentally. However, there are only few computational studies which are essential to understand the mechanistic aspects. We employ Molecular Dynamics (MD) simulations to establish a nanoscale atomistic model of the interfacial interactions of water on anatase (101) and rutile (110) surfaces with Pt atoms adsorbed. The highlight of our model is the large scale: we have simulated systems approximately 30 nm x 30 nm x 3 nm for a time interval spanning over 4 ns.

A combination of Monte Carlo and molecular dynamics simulations was carried out to estimate mixed CO2/CH4 adsorption isotherms on illite surfaces in the presence of water. Three bulk phase mixture compositions are explored to study the effect of concentrations on competitive sorption in illite bearing two positions for the isomorphic substitutions. The computed isotherms are compared with those predicted for dry systems to deduce the effect of water on CO2 and CH4 interactions with the clay surfaces. The hydration of the counter-balancing ions in pore space is studied to evaluate sorption-desorption processes at the basal clay surfaces. Sensitivity parameters reflecting preferential CO2/CH4 sorption, density profiles, and surface occupancy times are reported and analyzed.

Highly branched polymers such as polyamidoamine (PAMAM) dendrimers are promising macromolecules in the realm of nanobiotechnology due to their high surface coverage of tunable functional groups. Modeling efforts of PAMAM can provide structural and morphological properties, but the inclusion of solvents and the exponential growth of atoms with generations make atomistic simulations computationally expensive. We apply an implicit solvent coarse-grained model, called the Dry Martini force field, to PAMAM dendrimers. The reduced number of particles and the absence of a solvent allow the capture of longer spatiotemporal scales. This study characterizes PAMAM dendrimers of generations one through seven in acidic, neutral, and basic pH environments. Comparison with existing literature, both experimental and theoretical, is done using measurements of the radius of gyration, moment of inertia, radial distributions, and scaling exponents. Additionally, ion coordination distributions are studied to provide insight into the effects of interior and exterior protonation on counter ions. This model serves as a starting point for future designs of larger functionalized dendrimers.

Separating oil from saltwater is a process relevant to some industries and may be aided by bubble and froth generation. Simulating saltwater-air interfaces adsorbed with surfactants and oil molecules can assist in understanding froth stability to improve separation. Combining with surface tension experimental measurements, in this work we employ molecular dynamics with a united-atom force field to linear alkane oil and three surfactant frothers, methyl isobutyl carbinol (MIBC), terpineol, and ethyl glycol butyl ether (EGBE), to investigate their synergistic behaviors for oil separation. The interfacial phenomena were measured for a range of frother surface coverages on saltwater. Density profiles of the hydrophilic and hydrophobic portions of the frothers show an expected orientation of alcohol groups adsorbing to the polar water. A decrease in surface tension with increasing surface coverage of MIBC and terpineol was observed and reflected in experiments where the frother concentration increased. Relations between surface coverage and bulk concentration were observed by comparing the surface tension decreases. Additionally, a range of oil surface coverages was explored when the interface has a thin layer of adsorbed frother molecules. The obtained results indicate that an increase in surface coverage of oil molecules led to an increase in surface tension for all frother types and the pair correlation functions depicted MIBC and terpineol as having higher distributions with water at closer distances than with oil.

For water treatment purposes, the separation processes involving surfactants and crude oil at seawater-air interfaces are of importance for the chemical and energy industries. Little progress has been made in understanding the nanoscale phenomena of surfactants on oily saltwater-air interfaces. This work focuses on using molecular dynamics with a united-atom force field to simulate the interface of linear alkane oil, saltwater, and air with three surfactant frothers: methyl isobutyl carbinol (MIBC), terpineol, and ethyl glycol butyl ether. For each frother, although the calculated diffusivities and viscosities are lower than the expected experimental values, our results show that diffusivity trends between each frother agree with experiments but the method cannot be applied for viscosity. Binary combinations of liquid (frother or saltwater)-air and liquid-liquid interfaces are equilibrated to study the density profiles and interfacial tensions. The calculated surface tensions of the frother-air interfaces are like that of oil-air, but lower than that of saltwater-air. Only the MIBC-air and terpineol-air interfaces agreed with our experimental measurements. For the frother-saltwater interfaces, the calculated results showed that terpineol has interfacial tensions higher than those of MIBC-saltwater. The simulated results indicate that the frother-oil systems underwent mixing such that the density profiles depicted large interfacial thicknesses.

Through implicit solvent coarse-grained molecular dynamics simulations, we investigate the equilibrium morphologies resulting from the self-assembly of building blocks composed of anisotropically functionalized icosahedral viral capsid nanoparticles (NPs). We investigate the self-assembled aggregate morphologies for variations in the functional group chain length and solvent quality. We observe specific building block architectures to favor the formation of n-mers, chain- and network-like structures. Our work is in agreement with the earlier simulation studies on icosahedral gold nanocrystals that generate self-assembled chain-like structures. [G. Bilalbegovic, Comput. Mater. Sci. 31, 181 (2004).] In addition, our results agree with those by Finn et al., who have shown small predominantly chain-like aggregates with mannose-decorated cowpea mosaic virus (CPMV) [K.S. Raja, Q. Wang, and M.G. Finn, ChemBioChem 4, 1348–1351 (2003)] and small aggregates with oligonucleotide functionalization on the CPMV capsid. [E. Strable, J.E. Johnson, and M.G. Finn, Nano Lett. 4, 1385–1389 (2004).] Visual inspection suggests that our results most likely span the low temperature limits explored by Finn et al. and show a good degree of agreement with the experimental results at an annealing temperature of 4 °C. [E. Strable, J.E. Johnson, and M.G. Finn, Nano Lett. 4, 1385–1389 (2004).] Our investigations reveal the possibility of novel n-mer type aggregates that could be synthesized using icosahedral NPs with appropriate surface functionalization and solvent conditions.

Interfacial phenomena arising at solid/fluid interfaces depend upon the nanoscale structural and dynamical properties of the system. The presence of active sites on the solid surface that can bind with reactants in the fluid enables the investigation of reaction kinetics and its effect on multi-scale transport processes. We develop a coarse-grained particle-based model of the flow of reactants over a solid surface composed of close packed particles with embedded active sites. We investigate the role of the adsorption of the reactants onto these sites on the transport phenomena via the coarse-grained molecular dynamics technique. Our objective is to understand the role of nanoscale interfacial phenomena on the structural and dynamical properties of the system through the measurement of diffusion coefficients, velocity profiles, radial distribution functions, and mean residence times. We have investigated these properties as a function of the active site density, coarse graining effects and interaction strengths. Our results can potentially be used for future studies on multi-scale phenomena driven by reaction kinetics at solid/fluid interfaces, such as artificial photosynthesis cells.