Effect of pH and hydration on the normal and lateral interaction forces between alumina surfaces

Interaction forces between alumina surfaces were measured using an AFM–colloid probe method at different pHs. For an α-alumina–sapphire system at acidic pH, the force curve exhibited a well-defined repulsive barrier and an attractive minimum. At basic pH, the interactive force was repulsive at all separations with no primary minimum. Lateral force measurements under the same conditions showed that frictional forces were nearly an order of magnitude smaller at basic pH than those observed at acidic pH. This behavior was attributed to the hydration of the alumina surface. Normal and lateral force measurements with the strongly hydrated ρ-alumina surfaces supported these findings.

Graphical abstractNormal forces measured by colloid probe method between alumina surfaces were always repulsive at basic pH where the frictional forces also decreased significantly compared to those observed at acidic pH. Most probable reason is hydration of the surfaces.Figure optionsDownload full-size imageDownload as PowerPoint slide