Measurement of mobility of adsorbed colloids by lateral force microscopy

The surface mobility of colloidal latex particles adsorbed on mica was measured by moving the particles with an AFM tip in the lateral force microscopy mode. The same particle was repeatedly scanned while the normal force was gradually increased, until the particle was displaced from its location on the substrate. The lateral (friction) force curve obtained for that scan was then used to determine the force needed to displace the particle. The data accumulated for approximately 100 particles indicate a wide distribution in the lateral force required. However, the data show that the mean lateral force is proportional to the particle diameter, with the effect of electrostatic interactions on the mobility of adsorbed particles seen to be weak. These results are consistent with classical theories of friction in macroscopic systems.