Experimentally derived sticking efficiencies of microparticles using atomic force microscopy

The sticking efficiencies (alpha) of colloidal particles have been derived from the intersurface potential energy between 2 microm carboxylated polystyrene microspheres and a silica glass plate using the interaction force boundary layer model. The intersurface potential energies were calculated from force-distance data measured using atomic force microscopy (AFM) and from calculations based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. AFM forces were measured in aqueous solutions over a range of pH and ionic strength conditions, and DLVO calculations were performed on identical systems. In most conditions, sticking efficiencies that were calculated from AFM data are considerably largerthan values calculated from DLVO predictions. Sticking efficiencies vary between 0 and 1 and are strongly dependent upon solution chemistry. AFM-derived sticking efficiencies are consistent with measured microsphere and collector zeta-potentials; sticking efficiencies are lower for more negatively charged surfaces. These results provide the first alpha estimates of a microparticle-collector system that are calculated directly from physically measured interfacial nanoforces. This study clearly demonstrates that significant differences exist between DLVO- and AFM-derived sticking efficiencies.