The effect of the electrical double layer on hydrodynamic lubrication: a non-monotonic trend with increasing zeta potential.

Dalei Jing,Xiaoming Wang,Yunlu Pan

doi:10.3762/bjnano.8.152

Abstract

In the present study, a modified Reynolds equation including the electrical double layer (EDL)-induced electroviscous effect of lubricant is established to investigate the effect of the EDL on the hydrodynamic lubrication of a 1D slider bearing. The theoretical model is based on the nonlinear Poisson–Boltzmann equation without the use of the Debye–Hückel approximation. Furthermore, the variation in the bulk electrical conductivity of the lubricant under the influence of the EDL is also considered during the theoretical analysis of hydrodynamic lubrication. The results show that the EDL can increase the hydrodynamic load capacity of the lubricant in a 1D slider bearing. More importantly, the hydrodynamic load capacity of the lubricant under the influence of the EDL shows a non-monotonic trend, changing from enhancement to attenuation with a gradual increase in the absolute value of the zeta potential. This non-monotonic hydrodynamic lubrication is dependent on the non-monotonic electroviscous effect of the lubricant generated by the EDL, which is dominated by the non-monotonic electrical field strength and non-monotonic electrical body force on the lubricant. The subject of the paper is the theoretical modeling and the corresponding analysis.

Highlights

As one of the oldest techniques in modern engineering, lubrication is widely recognized and has inspired significant scientific interest [1,2,3,4]
After establishing the theoretical model regarding the effect of the electrical double layer (EDL) on the hydrodynamic lubrication, NaCl solution was chosen as the lubricant to carry out the analysis
To illustrate the differences induced by the Debye–Hückel approximation (DHA), the curves shown in Figure 2 are obtained by applying both the linear Poisson–Boltzmann equation (PBE) and the nonlinear PBE, respectively

Summary

Introduction

As one of the oldest techniques in modern engineering, lubrication is widely recognized and has inspired significant scientific interest [1,2,3,4]. Considering the small dimension of the fluid lubrication film (on the micro/nanoscale in the thickness direction), the chemical and physical properties of the solid–lubricant interface play an important role on the lubrication Among these interfacial properties, the effect of charged frictional pair–lubricant interface and the resulting electrical double layer (EDL) within the lubricant have been recognized and studied [5,6,7,8,9,10,11,12,13]. Zhang and Umehara [7] introduced the effect of the EDL on modifying the conventional Reynolds equation, analyzing the hydrodynamic lubrication They found that the minimum lubricant film thickness increased with the increasing absolute value of zeta potential (an important parameter of EDL to manifest the surface charge at the solid–liquid interface). Both of these two bearing surface–lubricant interfaces are negatively charged and have the same zeta potential, ζ

The lubricant film thickness is much larger than the

Results and Discussion

Conclusion