Interaction force measurements were performed for a silica-silica hydrophilic system and for a silanated silica-silanated silica hydrophobic system using the atomic force microscopy colloidal probe technique. The influence of the solution composition on interaction forces was investigated. The hydrophilic silica-silica interactions were found to be described as a typical Derjaguin-Landau-Verwey-Overbeek (DLVO) system in solutions of various compositions, whereas silanated silica-silanated silica interactions were dominated by a long-range hydrophobic force. All increase in the isopropyl alcohol content of the solution diminishes both the repulsive forces in the case of the hydrophilic system and the attractive interactions in the case of the hydrophobic system.