Autonomous pump against concentration gradient

Abstract

Using non-equilibrium molecular dynamics and Monte Carlo methods, we have studied the molecular transport in asymmetric nanochannels. The efficiency of the molecular pump depends on the angle and apertures of the asymmetric channel, the environmental temperature and average concentration of the particles. The pumping effect can be explained as the competition between the molecular force field and the thermal disturbance. Our results provide a green approach for pumping fluid particles against the concentration gradient through asymmetric nanoscale thin films without any external forces. It indicates that pumping vacuum can be a spontaneous process.

Figure 1

Diagram of the asymmetric carbon nanochannels; the insets (a,b) are side section and cross section of the nanotube, respectively.

Figure 2

Diagrams of asymmetric carbon nanotubes with various angles, (a) the cross section, (b) side section.

Figure 3

Force distribution in the asymmetric nanotubes with different angles: (a) 19.2°, (b) 38.9°, and (c) 60.0°. The dash lines are the walls of nanochannels.

Figure 4. Temperature dependence of the unit diffusion flux of He in different asymmetric nanotubes.

Figure 5

The probability distribution of atoms at the right (a) and left (b) entrance.

Figure 6. The average concentration dependence of the unit diffusion flux of helium.

The angle of asymmetric channel is 38.9°, which refers to the corresponding carbon nanotubes in Fig. 2.

Figure 7. Temperature dependence of the unit diffusion flux of Ne in different asymmetric nanotubes.

Figure 8. The right side concentration difference dependence of the unit diffusion flux with left side concentration fixed; normal diffusion and pumping effect mean the particle flux is along or against with the concentration gradient, respectively.

Figure 9. Asymmetric nano thin film for pumping vacuum.