Forces measured between latex spheres in aqueous electrolyte: Non-DLVO behavior and sensitivity to dissolved gas

An atomic force microscope was used to measure the forces acting between tw o polystyrene latex spheres in aqueous media. The results show an electrost atic repulsion at large separations which is overtaken by an attractive "ho ok" that pulls the two spheres into contact from a considerable range (20-4 00 nm), much larger than could be expected for a van der Waals attraction. The range of operation of this attraction varies from one experiment to ano ther and is not correlated with electrolyte concentration. However, the ran ge is found to decrease significantly when the level of dissolved gas in th e water is reduced.