Influence of Adsorption Characteristics of Surfactants Sodium Dodecyl Sulfate and Aerosol–OT on Dynamic Process of Water-Based Lubrication

Abstract

Surfactant solutions are widely used in industry, and their steady-state lubrication properties have been comprehensively explored, while the “dynamic process” between steady states attracts much less attention. In this study, the lubrication behaviors of sodium dodecyl sulfate (SDS) and sodium bis (2–ethylhexyl) sulfosuccinate (Aerosol–OT, AOT) solutions were comparatively and extensively discussed. Experimental results showed that the duration of the dynamic process of AOT solution lubrication was significantly shorter than that of SDS. The essence of the dynamic process was revealed from the aspects of the running-in of solid surfaces and the adsorption process of surfactant molecules. Unlike the general recognition that the friction force evolution mainly corresponds to the running-in of surfaces, this study indicated that the dynamic adsorption behavior of surfactant molecules mainly contributes to this process. Various experiments and analyses showed that the smaller steric hindrance and lower orientation speed of SDS molecules led to longer diffusion into the confined contact zone and a longer duration of friction force decrease. This work enhances our understanding of the dynamic friction process in water-based lubrication, which could also have important implications for oil-based lubrication and its industrial applications.