Molecular Dynamics Simulation of Composite Nanochannels as Nanopumps Driven by Symmetric Temperature Gradients

In this Letter, we propose a composite nanochannel system, where half of the channel is of low surface energy, while the other half has a relatively high surface energy. Molecular dynamics simulations show that fluids in such channels can be continuously driven by a symmetric temperature gradient. In the low surface energy part, the fluid moves from high to low temperature, while the fluid migrates from low to high temperature in the high surface energy part. The mechanisms that govern the flow are explained and the conditions required to guarantee the flow and the possible applications are discussed.

Figure 1

Structure of the composite nanochannel system under a symmetric temperature gradient. Green particles are liquid molecules, which are in connection with two reservoirs. The left half of the wall (orange) has low and the right half (gray) has high surface energy. The temperature in the middle is higher than that at the ends of the channel.

Figure 2

The volumetric flux of the liquid as a function of ${\epsilon }_{\mathrm{fw}(L)}$ at different temperature gradients in a 4 nm channel. The fluid-wall binding energy in the right half of the channel ${\epsilon }_{\mathrm{fw}(R)}=500\mathrm{K}$ and $T_L=100\mathrm{K}$.

Figure 3

Two-dimensional contour plots of (a) density, (b) temperature, and (c) pressure distribution in the channel for the flow in a 4 nm channel with $T_H=600$ and $T_L=100\mathrm{K}$. The fluid-wall binding energy ${\epsilon }_{\mathrm{fw}(L)}=10$ and ${\epsilon }_{\mathrm{fw}(R)}=500\mathrm{K}$. The thin color strip in (b) shows the temperature in the wall.

Figure 4

The velocity field in a 4 nm channel with $T_H=600$ and $T_L=100\mathrm{K}$. (a) ${\epsilon }_{\mathrm{fw}(L)}=10$ and ${\epsilon }_{\mathrm{fw}(R)}=500\mathrm{K}$. (b) ${\epsilon }_{\mathrm{fw}(L)}=200$ and ${\epsilon }_{\mathrm{fw}(R)}=500\mathrm{K}$.

Figure 5

The reduced volumetric flux as a function of ${\epsilon }_{\mathrm{fw}(L)}$ in 2, 4, and 6 nm channels (a),(b) and for different fluid densities (c),(d) with ${\epsilon }_{\mathrm{fw}(R)}=500\mathrm{K}$ and $T_L=100\mathrm{K}$. In (c) and (d), the channel width is 4 nm.