Role of non-ionic surfactants in adhesive forces between surfaces in moist cyclohexane

The role of various non-ionic surfactants in the adhesive force between a mica plate and a SiO2 surface in moist cyclohexane is investigated using an atomic force microscope (AFM). It is found that the adhesive force decreases with both increasing concentration of surfactants and the value of the hydrophile-lipophile balance (HLB); furthermore, the hydrophilic surfactant with the highest HLB, polyoxyethylene dodecylether (C12E9), has nearly the same ability for adhesion reduction as the ionic surfactant sodiumbis (2-ethylhexyl) sulfosuccinate (AOT). However, it is estimated that there is a difference in the mechanisms of the two surfactants: in the case of AOT, water is removed from the surface because water is dissolved as micelles with AOT, but, in the case of C12E9, water is not only solubilized but also captured by C12E9 with the long hydrophilic chain on the surface so that sufficient water cannot be supplied for bridging.