The Rheological Properties of Nanoscale Fluid

Abstract

Nonequilibrium molecular dynamics simulation is used to simulate the rheological properties of the nanoscale fluid. A physical model of the “bulk – nanochannel – bulk” that resembles a fluid film confined between two solid walls was simulated. The simulation is performed at variable wall speeds, nanochannel heights and surface charge densities. Simulation results indicate that the effective densities of water decrease with the size as the channel size below 1 nm when the surface charge density is −0.30 C/m2. And it is also demonstrated that the water density increases with the surface charge density. The fluid viscosity keeps at around 1.78 cp when the thickness of the film more than 1.5 nm, the −0.30 C/m2 surface charge density and the 5×1010 S−1 shear rate, which is quite close to the bulk value. The fluid viscosity keeps at around 1.69 cp when the surface charge density is −0.15 C/m2, and 1.28 cp when the surface density is 0 C/m2. In addition, the shear rate shows strong influence on the nanoscale fluid film. Compare to the surface density −0.30 C/m2 and −0.15 C/m2, the fluid density of the 0 C/m2 has different properties when the shear rate varied from 0.1×011 S−1 to 1.0×1011 S−1. Especially, when the nanochannel height is 0.8 nm, the shear viscosity begins to increase and reach the peak when the shear rate is 0.2×1011 S−1, then the shear viscosity decreases with the shear rate increase. The shear viscosity of the height of 2.5 nm and 3.0 nm show a constant value which is quite close to the bulk value, and shear viscosity of 1.5 nm height increases and reaches plateau when the shear rate exceeds 0.2×1011 S−1.