OIL DROPLET INTERACTION WITH A QUARTZ SURFACE IN SOLUTIONS OF CATIONIC SURFACTANTS

Contact angles of oil droplets on a quartz surface, emulsion-film thic knesses between the surfaces of quartz and oil, and their surface char ges were measured over a wide range of the cationic CTAB concentration s in the background electrolyte solution (10(-4) M KCl). Oil droplet m otion in a CTAB solution and the processes of mutual displacement were studied in thin capillaries. Tetradecane and silicone oil were used a s the model systems. The equilibrium contact angles calculated from th e disjoining pressure isotherms closely approximated their experimenta l counterparts. The calculations were performed with due regard for mo lecular, electrostatic, and hydrophobic attraction forces. The electro static and hydrophobic forces were shown to make the greatest contribu tion to droplet adhesion. As the CTAB concentration increased to 10(-3 ) M, adhesion decreased sharply because of the hydrophilization of the oil and quartz surfaces and their high positive charge. The data obta ined point to the possibility of controlling droplet adhesion by catio nic surfactants.