Boundary slip and wetting properties of interfaces: Correlation of the contact angle with the slip length

Abstract

Correlations between contact angle, a measure of the wetting of surfaces, and slip length are developed using nonequilibrium molecular dynamics for a Lennard-Jones fluid in Couette flow between graphitelike hexagonal-lattice walls. The fluid-wall interaction is varied by modulating the interfacial energy parameter epsilonr=epsilonsfepsilonff and the size parameter sigmar=sigmasfsigmaff, (s=solid, f=fluid) to achieve hydrophobicity (solvophobicity) or hydrophilicity (solvophilicity). The effects of surface chemistry, as well as the effects of temperature and shear rate on the slip length are determined. The contact angle increases from 25 degrees to 147 degrees on highly hydrophobic surfaces (as epsilonr decreases from 0.5 to 0.1), as expected. The slip length is functionally dependent on the affinity strength parameters epsilonr and sigmar: increasing logarithmically with decreasing surface energy epsilonr (i.e., more hydrophobic), while decreasing with power law with decreasing size sigmar. The mechanism for the latter is different from the energetic case. While weak wall forces (small epsilonr) produce hydrophobicity, larger sigmar smoothes out the surface roughness. Both tend to increase the slip. The slip length grows rapidly with a high shear rate, as wall velocity increases three decades from 100 to 10(5) ms. We demonstrate that fluid-solid interfaces with low epsilonr and high sigmar should be chosen to increase slip and are prime candidates for drag reduction.

Fast mass transport of oil and supercritical carbon dioxide through organic nanopores in shale

“…We attribute the reverse dependence of L s $ T to the distinct affinities of silica and graphene for hydrocarbons. This result supports the insights of Voronov et al [60], who studied the correlation of boundary slip and wetting properties using Couette flow simulations (NEMD) of LJ particles by varying the relative affinities and suggested that the temperature exhibits a very complex effect on the slip length, depending on the intermolecular interactions. At a given pressure gradient, an increase in temperature still enhances the flow of liquid alkanes in an organic slit, even though the slip length is becoming smaller.…”

“…The upward trend of slip length upon heating is qualitatively consistent with the results of a quartz-octane system [41] but opposite to that observed for OM-octane (Fig. 6), which demonstrates that the dependence of slip length on temperature is very complicated, as suggested by Voronov et al [60].…”

Molecular dynamics-based prediction of boundary slip of fluids in nanochannels

“…Thus, as increasing the number density of the solid wall, the decrease of the corrugation play the dominant role, resulting in the increase of the boundary slip. The temperature of the confined fluid represents the thermal vibration of the fluid molecules, which can reduce the fluid-solid binding if the temperature is high (Voronov et al 2006;Li 2009b). To obtain the identical equilibrium pressure of the fluid for different fluid temperature, the Fig.…”

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

“…Fluid adsorption on solid surfaces is generally determined by the ratio of fluid-wall binding energy to temperature, " fw =kT [17][18][19][20][21][22]. This ratio expresses the competition between the fluid-wall binding strength and the kinetic energy of the fluid.…”