Microparticle adhesion studies by atomic force microscopy

Atomic force microscopy (AFM) is one of the most flexible and simple techniques for probing surface interactions. This article reviews AFM studies on particle adhesion. Special attention is paid to the characterization of roughness and its effect on adhesion. This is of importance when comparing the measured adhesion forces to theoretical values, as the contact area is included in the contact mechanics theories. Even though adhesion models for time-independent adhesion are reasonably well developed, it remains difficult to connect the measured values to model predictions, especially because of the unknown value of the true contact area. The true area of contact depends on both the roughness of the probe as well as of the substrate. Our studies on the interactions between smooth silica particles, or rougher toner particles, and silicon substrates as a function of the surface roughness of the latter has shown the utility of AFM for measuring both roughness and particle adhesion.