Lateral force microscopy investigation of surfactant-mediated lubrication from aqueous solution

Chemisorbed and deposited self-assembled films have been extensively studied in the past in terms of the lubrication induced from chain properties and interactions; however, few studies have investigated the frictional interactions that occur from physically adsorbed self-assembled surfactant structures that are dynamically formed from solution. In this study, the nanoscale tribology of silica surfaces mediated by self-assembled films of quarternary ammonium surfactant aggregates, above and below the critical micelle concentration, is investigated through lateral force microscopy. It is illustrated that in addition to surfactant-surfactant cohesion the extent of surfactant-surface adhesion can be used to modify and predict the frictional interactions of particulates and surfaces stabilized by self-assembled surfactant films. It is further demonstrated that the extent of friction and onset of the transition between boundary layer lubrication and bare surface engagement between interfaces can be manipulated by altering the affinity of the surfactant headgroup to the surface through the adjustment of the number of high-affinity surface adsorption sites and the amount of competing ionic species in solution. These findings may lead to the development of smart surfactant-based lubrication schemes, which have the ability to self-heal or disappear when necessary.