Monte Carlo study of structural ordering of Lennard-Jones fluids confined in nanochannels

Efficient Transport Between Disjoint Nanochannels by a Water Bridge

Water channels are important to new purification systems, osmotic power harvesting in salinity gradients, hydroelectric voltage conversion, signal transmission, drug delivery, and many other applications. To be effective, water channels must have structures more complex than a single tube. One way of building such structures is through a water bridge between two disjoint channels that are not physically connected. We report on the results of extensive molecular dynamics simulation of water transport through such bridges between two carbon nanotubes separated by a nanogap. We show that not only can pressurized water be transported across a stable bridge, but also that (i) for a range of the gap's width l_{g} the bridge's hydraulic conductance G_{b} does not depend on l_{g}, (ii) the overall shape of the bridge is not cylindrical, and (iii) the dependence of G_{b} on the angle between the axes of two nonaligned nanochannels may be used to tune the flow rate between the two.

Nanojunction Effects on Water Flow in Carbon Nanotubes

We report on the results of extensive molecular dynamics simulation of water imbibition in carbon nanotubes (CNTs), connected together by converging or diverging nanojunctions in various configurations. The goal of the study is to understand the effect of the nanojunctions on the interface motion, as well as the differences between what we study and water imbibition in microchannels. While the dynamics of water uptake in the entrance CNT is the same as that of imbibition in straight CNTs, with the main source of energy dissipation being the friction at the entrance, water uptake in the exit CNT is more complex due to significant energy loss in the nanojunctions. We derive an approximate but accurate expression for the pressure drop in the nanojunction. A remarkable difference between dynamic wetting of nano- and microjunctions is that, whereas water absorption time in the latter depends only on the ratios of the radii and of the lengths of the channels, the same is not true about the former, which is shown to be strongly dependent upon the size of each segment of the nanojunction. Interface pinning-depinning also occurs at the convex edges.

Elastic properties of a confined fluid

Monte Carlo computer simulation is employed to determine the local, wave-number-dependent, high-frequency elastic properties of a Lennard-Jones fluid that is confined between two walls. In particular, the elastic constants are calculated from coarse-grained stress correlation functions and then related to the local fluid structure via planar radial distribution functions. We find that local fluid properties correlate with the inhomogeneous fluid density and the strength of the wall-fluid interaction. Finally, we discuss the utility of this analysis in the interpretation of experiments involving the characterization of confined fluids.