Water inside a nanocapillary becomes ordered, resulting in unconventional behavior. A profound enhancement of water flow inside nanometer thin capillaries made of graphene has been observed [B. Radha et.al., Nature (London) 538, 222 (2016)]. Here we explain this enhancement as due to the large density and the extraordinary viscosity of water inside the graphene nanocapillaries. Using the Hagen-Poiseuille theory with slippage-boundary condition and incorporating disjoining pressure term in combination with results from molecular dynamics (MD) simulations, we present an analytical theory that elucidates the origin of the enhancement of water flow inside hydrophobic nanocapillaries. Our work reveals a distinctive dependence of water flow in a nanocapillary on the structural properties of nanoconfined water in agreement with experiment, which opens a new avenue in nanofluidics.

No abstract

Nonequilibrium molecular dynamics simulations is used to study the motion of a C60 molecule on a graphene sheet subjected to a temperature gradient. The C60 molecule is actuated and moves along the system while it just randomly dances along the perpendicular direction. Increasing the temperature gradient increases the directed velocity of C60. It is found that the free energy decreases as the C60 molecule moves toward the cold end. The driving mechanism based on the temperature gradient suggests the construction of nanoscale graphene-based motors.

The dynamics of a water nano-droplet on a flexible graphene sheet, in the presence of constant and alternative electric fields with various amplitudes and frequencies, was considered using a molecular dynamics method. It was found that because the water molecules respond to electric field, the nano-droplet elongates in the field direction for a field amplitude larger than 0.08 V Å, which is stronger than the predicted value from the Young-Laplace equation. This difference can be described by considering the van der Waals attractions between the droplet molecules and the substrate, which can be calculated by modifying the Young-Laplace equation. Furthermore, under the influence of an alternating field over the GHz frequency range, it was shown that the droplet shape will not change above a threshold frequency, which depends on the relaxation time of the water dipole.

No abstract

No abstract

Crack propagation in a defected graphene sheet is investigated at finite temperature using molecular dynamics simulation. The effects of several initial cracks, temperature and different percentage of vacancies are considered. It is found that i) the critical load, which is a criteria for crack propagation, is larger when the load is applied on the zigzag direction, ii) the critical load decreases with increasing temperature, iii) a hole in the center of the sheet and the presence of randomly distributed vacancies reduce the critical load giving different crack propagation trajectory. Our new results would help to understand the crack propagation phenomena in defected graphene at finite temperature.

No abstract