The boundary lubrication of glass-glass contacts by mixed alkyl alcohol and cationic surfactant systems

We report a preliminary investigation of the consequences for boundary lubricant performance of incorporating alkyl alcohols into aqueous solutions of quaternary ammonium chloride surfactants. Frictional data taken under single and multi-pass linear sliding conditions are presented for glass sphere-glass flat contacts lubricated by quat/alcohol mixtures and their individual components; the effects of varying chain length, sliding velocity, sliding cycles and contact pressure have been examined and the results used to calculate interfacial shear rheological data for these systems. An interpretation of the data is given in terms of the existing boundary lubrication literature. As demonstrated in studies by earlier workers, the friction was found to increase sharply for alkyl chain lengths below C14. For C16 mixtures the results indicate that the principal effect of incorporating the alcohol is to increase the contact pressure at which damage appears to occur, as judged by an increase in interfacial shear strength, rather than to reduce the magnitude of the friction per se. Dried films reduced the susceptibility to contact damage compared to their undried analogues, as might be expected; a more surprising finding was the marked sensitivity of the critical contact pressure, corresponding to the initiation of damage, to the contact diameter.