Applying the quartz crystal microbalance technique to determine the stability of colloidal suspensions

Colloidal suspension behaviour is strongly influenced by the particle - particle interaction forces operative in the system. The stability of aqueous suspensions can be manipulated though the addition of electrolyte and changes in the pH. Such adjustments affect the net surface charge of the particles and/or the thickness of the diffuse electrical double layer (edl) surrounding the particles. If the charge or the double layer is sufficiently reduced, the ubiquitous attractive van der Waals interaction forces can dominate and the dispersion is destabilized. A Quartz Crystal Microbalance with dissipation monitoring (QCM-D) is used to measure the degree of destabilisation in a particle suspension. Mono-dispersed silica suspensions were prepared in several different chemical environments, with the conditions chosen from examination of the zeta potential and sedimentation data. The study shows that by varying the suspension stability, the resonating frequency of the 5MHz AT-cut quartz silica crystal, significantly deviates as the amplitude of oscillation is increased for a coagulated suspension, whilst remaining unchanged for a dispersed suspension.