DIRECT FORCE MEASUREMENTS BETWEEN DISSIMILAR METAL-OXIDES

An atomic force microscope has been used to measure the force of inter action between a SiO2 glass sphere (similar to 5 mu m diameter) and a TiO2 crystal, in an aqueous medium over the pH range 3-9. The force-se paration profiles obtained were compared with DLVO theory, which was f ound to adequately account for the experimental results up to separati ons of ca. 2 nm. At distances below this point repulsive interactions in excess of DLVO may be present under certain conditions. To compleme nt the diffuse layer potential results extracted from the force-separa tion data for dissimilar materials, force-separation interactions were also measured between two SiO2 glass spheres. For both sets of surfac es, modeling of the experimental force-separation curves was best achi eved using constant-charge rather than constant-potential boundary con ditions.