SURFACE AND CAPILLARY FORCES AFFECTING AIR BUBBLE-PARTICLE INTERACTIONS IN AQUEOUS-ELECTROLYTE

The interaction between hydrophilic silica particles and air bubbles i n aqueous electrolyte has been studied by colloid probe atomic force m icroscopy. The interaction was found to be monotonically repulsive on approach. The silica surface was also hydrophobized by dehydroxylation and by treatment with octadecyltrichlorosilane (OTS). In these cases a repulsion was observed at long range with an attraction evident as t he bubble-particle separation decreased. For a freshly prepared OTS-si lica surface the intervening thin film rapidly collapsed, resulting in particle engulfment or establishment of a three-phase line. For an ag ed OTS-silica surface a stable film was formed which could be ruptured as the loading force was increased. In all cases adhesion resisted bu bble-particle separation. This behavior was rationalized in terms of e ither attractive surface forces or capillary forces and contact angle hysteresis operating after formation of a three-phase line (TPL).