INTERFACIAL AGGREGATION OF A NONIONIC SURFACTANT - EFFECT ON THE STABILITY OF SILICA SUSPENSIONS

The adsorption of the nonionic surfactant TX100 in two silica suspensi ons (Ludox HS40 and Syton W30) has been studied with the aim of relati ng the structure of the adsorbed layer to the stability of the suspens ion. First, a thermodynamic study based on the determination of adsorp tion isotherms and displacement enthalpies as a function of pH and sol id/liquid ratio was carried out and lead to the conclusion that such a surfactant forms micelle-like aggregates on the silica surface. Then, a stability study based on visual observation, turbidimetry, and part icle size determination (by photon correlation spectroscopy) was perfo rmed in order to determine the TX100 concentration range in which floc culation occurs. Considering that the surface is covered with micelle- like aggregates in the flocculation range and that the zeta-potential (determined by microelectrophoresis) has varied only slightly at the o nset of flocculation, it is concluded that the flocculation mechanism is a bridging of particles by surface micelles. This bridging of parti cles by aggregates similar in size and shape could be an explanation o f the presence, in such systems, of optimum flocculation at half surfa ce coverage. (C) 1994 Academic Press, Inc.