DIRECT MEASUREMENT OF COLLOIDAL FORCES BETWEEN MICA AND SILICA IN AQUEOUS-ELECTROLYTE

A refined methodology which allows attachment of submicrometer colloid al particles to atomic force microscopy cantilevers is described. The interactions between particles of this size and both mica and silica s urfaces in aqueous electrolyte at pH 5.8 have been studied. The monoto nic repulsive force observed was in all cases well fitted by assuming that the force was due to overlap of electrical double layers. The pot ential of a cleaved mica surface was found to be significantly less th an that of the silica surface. However, the mica potential was found t o increase, if the mica surface was immersed immediately (within secon ds) in electrolyte after cleavage or after plasma cleaning. This behav ior is explained by the finite aqueous solubility of adventitious carb on that spontaneously deposits on mica after cleavage in air. The surf ace potential of the silica spheres was obtained by fitting symmetric interaction data. The trend in zeta potential of the silica spheres wi th pH, determined by particle electrophoresis, was similar to that obt ained from analysis of force-separation data. (C) 1997 Academic Press.