| Popis: |
Previous studies of surfactants as water-based lubrication additives have mainly focused on their steady-state behavior, but the “transition phase” between two steady states has been rarely studied, which is more or at least equally important for actual lubrication conditions. In this study, the lubrication behaviors of sodium dodecyl sulfate (SDS) and sodium bis (2-ethylhexyl) sulfosuccinate (Aerosol-OT, AOT) solutions were comparatively investigated under step-changed working conditions. It was found that the duration of the transition phase of AOT solution as lubricant was significantly shorter than that of SDS. During the transition phase, the contact zone experienced a slight running-in and fresh surfaces were created. Compared with SDS, the adsorption rate of AOT was higher, and its adsorption amount was lower due to the larger steric hindrance of the molecular structure. Therefore, the adsorption state of AOT in the contact zone could reach a new dynamic equilibrium faster, so that the friction coefficient would reach a stable value faster. Different from the common opinion that running-in is the cause of the transition phase of lubrication, this study indicates that the dynamic adsorption behavior of surfactant molecules mainly contributes to this process, which should be paid more attention to guide their industrial applications. |
