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A systematic molecular dynamics study shows that the contact angle of a water droplet on graphite changes significantly as a function of the water−carbon interaction energy. Together with the observation that a linear relationship can be established between the contact angle and the water monomer binding energy on graphite, a new route to calibrate interaction potential parameters is presented. Through a variation of the droplet size in the range from 1000 to 17 500 water molecules, we determine the line tension to be positive and on the order of 2 × 10^-10 J/m. To recover a macroscopic contact angle of 86°, a water monomer binding energy of −6.33 kJ mol^-1 is required, which is obtained by applying a carbon−oxygen Lennard-Jones potential with the parameters εCO = 0.392 kJ mol^-1 and σCO = 3.19 Å. For this new water−carbon interaction potential, we present density profiles and hydrogen bond distributions for a water droplet on graphite.

We study the behavior of water droplets confined in a carbon nanotube by means of parallel molecular dynamics simulations. We report radial density profiles, radial hydrogen bond distributions, and contact angles for tube radii ranging from 12.5 to 37.5 Å and for droplets containing up to 4632 water molecules. Our results indicate nonwetting behavior of the pristine CNT at room temperatures.

We study the structural properties of water surrounding a carbon nanotube using molecular dynamics simulations. The interaction potentials involve a description of the carbon nanotube using Morse, harmonic bending, torsion, and Lennard-Jones potentials. The water is described by the flexible Simple Point Charge (SPC) model by Teleman et al.,¹ and the carbon−water interactions include a carbon−oxygen Lennard-Jones potential, and an electrostatic quadrupole moment acting between the carbon atoms and the charge sites of the water. Vibration of the breathing mode of the carbon nanotube in water is inferred from the oscillations in carbon−carbon van der Waals energy, and the inverse proportionality between the radius of the carbon nanotube and the breathing frequency is in good agreement with experimental values. The results indicate, that under the present conditions, the presence of the water has a negligible influence on the breathing frequency. The water at the carbon−water interface is found to have a HOH plane nearly tangential to the interface, and the water radial density profile exhibits the characteristic layering also found in the graphite−water system. The average number of hydrogen bonds decreases from a value of 3.73 in the bulk phase to a value of 2.89 at the carbon−water interface. The inclusion of the carbon quadrupole moment is found to have a negligible influence on the structural properties of the water. Energy changes that occur by the process of introducing a carbon nanotube in water are calculated. The creation of a cavity in the bulk water to accommodate the nanotube constitutes the largest energy contribution. Results include an analysis of surface structure and energy values for planar and for concave cylindrical surfaces of water.

Simulation calculations are conducted for Si substrates to analyze the formation and diffusion energies of interstitials under strain condition using statics methods based on a Stillinger–Weber-type potential function. Defects in the vicinity of the surface region and in the bulk are examined, and the role played by compressive and tensile strains on the energetics of interstitials is investigated. The results indicate that strain alters defect energetics, which, in turn, modifies their diffusion characteristics.

Material properties for small clusters of nanometric dimensions were investigated. Calculations were carried out for spherical diamond and diamond-like particles containing over 1000 carbon atoms. Variations in the average cohesive energy, the excess surface energy and in the stiffness value were investigated as a function of the cluster size. Furthermore, energetic stabilities for spherical 3D clusters of carbon (in diamond-like atomic arrangements) were analyzed and compared with stabilities of other carbon clusters with lower dimensionalities.

Molecular dynamics calculations are carried out to investigate the effect exerted by aqueous solutions on the equilibrium structure and configuration of functional groups attached to carbon nanotubes. In this study, structures of polar and nonpolar functional groups in water are analyzed. Energy changes associated with configurational transformations of functional groups (from folded to extended forms) in water are calculated. Results indicate that polar functional groups are energetically more stable in extended configurations. Nonpolar functional groups, on the other hand, prefer to remain folded.