Interaction forces between muscovite and silica surfaces in electrolyte solutions measured with AFM

Interaction forces between a silica colloidal sphere and a muscovite flat surface in electrolyte solutions were directly measured with an atomic force microscope (AFM). The results showed a significant impact of time, electrolyte concentration and solution pH on both long-range (non-contact) and adhesion (pull-off) force. A strong long-range repulsive force was observed under conditions of lower electrolyte concentration and higher solution pH, while a weak long-range attractive force was observed in the higher electrolyte concentration and lower pH solutions. With the electrolyte concentration increasing, the interaction forces decreased from strong repulsive force to strong attractive force. The measured long-range forces were monotonically repulsive at pH 5.8-10.2 and changed in a small scale. However, when the solution pH decreased to 3.4, a weak attractive force was observed at a separation distance of 22-32 nm. In low electrolyte concentration and pH solutions, the adhesion force between the muscovite and silica is large. With increasing the electrolyte concentration and solution pH, the adhesion force decreased and became relatively stable at last. The measured interaction forces were fitted well with the classical DLVO theory.