Direct force measurements between titanium dioxide surfaces

An atomic force microscope (AFM) has been used to measure the force of interaction between a rutile titanium dioxide colloid and a single macroscopic rutile crystal in aqueous solution. The effect of pH and electrolyte concentration on the force has been investigated. {potentials were derived from electrophoretic mobility measurements on the rutile colloid as a function of pH and electrolyte concentration. Experimental decay lengths for the repulsive electrical double layer interaction are in good agreement with the theoretical Debye lengths at <1t2 M electrolyte. Measurements at the isoelectric point, i.e. pH = 5.6 of the Ti02, could be fitted with a nonretarded Hamaker constant of 6 f 2 J. This value agrees well with the van der Waals interaction calculated within the framework of the Lifshitz theory. In the calculation we used the Ninham-Parsegian representation for the dielectric susceptibility function and have utilized refractive index versus wavelength data to characterize the van der Waals interaction in rutile systems. A non-retarded Hamaker constant of 7 k 1 X 1C20 J was calculated for two rutile surfaces interacting across water. ~~~~