ADSORPTION OF THE POLY(OXYETHYLENE) NONIONIC SURFACTANT C12E5 TO SILICA - A STUDY USING ATOMIC FORCE MICROSCOPY

The forces between a spherical silica particle of colloidal dimension and a smooth silica surface have been measured in aqueous solution as a function of the concentration of the nonionic surfactant pentakis(oxyethylene) dodecyl ether. In the absence of surfactant the interaction between silica surfaces was purely repulsive, being composed of electrostatic and hydration forces, whereas at low surfactant concentrations (almost-equal-to 2 x 10(-5) M, about one-third the critical micelle concentration (cmc)) the repulsion was replaced at short separations by an attractive force which pulled the surfaces into adhesive contact. At higher concentrations (almost-equal-to 4 x 10(-5) M) the surfaces still experienced an attractive force at small separations, but the adhesion decreased markedly. At concentrations above the cmc repulsive steric forces are observed. A tentative scheme for the adsorption of poly(oxyethylene) surfactant to silica is presented.