Normal and lateral interaction of α-alumina in different electrolyte solutions

Ionic strength dependence of normal and friction forces between hydrophilic α-alumina particle and c-sapphire surface (0 0 0 1) was investigated at basic pH conditions using the colloidal probe method. The compression of the double layer could be seen from force–distance curves as the ionic strength of the solution increased. The forces were repulsive at low ionic strengths measured and jump to contact occurred at close enough separations. The repulsive interaction distance was about 25 nm in 10−3 M LiCl and CsCl solution and turned into attractive in 1 M LiCl and CsCl case. The lubricating effect of hydrated cations on the lateral friction force was demonstrated at high electrolyte concentrations. The reason was attributed to more hydrated cations present at the interface. The friction behavior was closely related to the short-range repulsive forces between the α-alumina surfaces at pH 11.