Dispersion properties of silica particles in nonaqueous media with a non-ionic surfactant, dodecyl hexaethylene glycol monoether, C12E6

An experimental programme is described that evaluated the role of charge and steric stabilisation in glycol and dodecane dispersions of colloidal silica particles on addition of trace water and acid. The surfactant used for steric stabilisation was a non-ionic surfactant, Dodecyl hexaethylene glycol monoether, C12E6 with a geometric head-to-tail length of 3.85 nm. The study showed using the self-consistent field theory of adsorption (SCFA), electrophoresis and electroacoustic sonic amplitude (ESA), that the C12E6 molecules adsorbed with the ethoxy group attached to the silica surface and the alkyl group in the bulk glycol solution. The thickness of the adsorbed layer as estimated from electrophoretic and viscosity measurements was found to be 8 and 10 nm, respectively, indicative of globular aggregation. The dispersions were stable at low levels of C12E6 concentrations due to electrostatic repulsions as deduced from the zeta potentials of silica which were of the order of about −30 to −50 mV in monoethylene glycol (MEG). Instability on further addition of C12E6 to the silica particles, a phenomenon normally obtained with high molecular weight polymers, was observed in MEG. Critical flocculation concentrations of C12E6, ϕfloc, increased with decrease in volume fraction of the silica particles in MEG. Instability is suggested to be from bridging interactions. Restabilisation observed at high surfactant concentration was due to steric repulsions of ethoxy groups of micellar aggregates adsorbed on silica particles. The study also revealed that the presence of trace water introduced charge repulsion which moderated rheological measurements in glycol media and introduced reversal of charge of silica particles in dodecane.