Meta-Analysis Comparing Wettability Parameters and the Effect of Wettability on Friction Coefficient in Lubrication

Abstract

This work presents a meta-analysis that compares the suitability of various parameters used to characterize wettability in tribological systems. It also examines the relationship between wettability and the friction factor for multiple lubricant-surface pairings. The characterization of wetting behavior was similar when using the contact angle between a lubricant and surface and various dimensional and dimensionless formulations of a spreading parameter. It was possible to identify hydrodynamic, boundary, and mixed lubrication regimes by combining a dimensionless wettability parameter with the specific film thickness for a variety of neat ionic liquids and magnetorheological fluids in contact with metallic, thermoplastic, and elastic surfaces. This characterization was possible using multiple dimensionless wettability parameters, but those that can be fully determined using only the contact angle may be preferred by experimentalists. The use of dimensional and dimensionless wettability parameters that included polar and disperse components of surface tension and surface energy did not appear to provide additional insight into the wettability or frictional performance for the tribological system examined here.

Towards programmable friction: control of lubrication with ionic liquid mixtures by automated electrical regulation

“…The applied bias voltage on the substrates also leads to a change in surface energy. Since the surface energy of the substrate and the surface tension of the lubricant influence the adhesion of the ions and thus the lubricating properties, the interfacial parameters of the system must be taken into account 35 – 37 . [P66614][BTA] (γ: 27.4 mN/m, 0.59 ratio polar/dispersive) has nearly the same surface tension but higher polarity than [P66614][DEHP] (γ: 30.5 mN/m, 0.19 ratio polar/dispersive).…”

Novel fatty acid anion-based ionic liquids: Contact angle, surface tension, polarity fraction and spreading parameter

“…Whenever solid-liquid interface is present in any application, knowing and understanding the wetting behavior through the different wetting parameters faced in this research (spreading parameter, polarity fraction, contact angle and surface tension) are mandatory in order to obtain a proper characterization of the involved phenomena occurring [65][66][67][68][69]. Despite the fact that this wetting study is not always addressed in lubrication science, obtaining different wetting parameters is interesting to design tribology contacts adequately [22,46,[49][50][51]64].…”

“…Because of the increasing research work using ionic liquids in lubrication in the last 18 years [24][25][26][27][28][29], it is important the study of key properties of these compounds, such us viscosity, density, wettability, thermal stability and tribofilm formation, which are closely related with lubrication [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. Therefore, tribology research should face the knowledge of wettability parameters with the aim of getting a better design of lubrication systems [47][48][49][50][51][52].…”

The Transition from Static to Dynamic Boundary Friction of a Lubricated Spreading and a Non-Spreading Adhesive Contact by Macroscopic Oscillatory Tribometry

“…Since Schallamach's approach is based on an energy-based description of the slip rate for adhesive processes between the frictional partners (Equation (1)), their surface and interfacial energies can give some insight into the influence of the lubricant on the adhesive friction (Equations (2) and (4)). A good correlation was found for wetting and spreading parameter of lubricated self-pairing contacts for a wide range of lubricants [11,12].…”