CHANGE OF THE RESONANCE FREQUENCY OF A QUARTZ-CRYSTAL MICROBALANCE INCONTACT WITH AN AQUEOUS DISPERSION OF SOLID PARTICLES

The change of resonance frequency of shear oscillations of an AT-cut q uartz crystal with a resonance frequency f(0) of f(0) = 5 MHz operated with one face in contact with air and the other in contact with an aq ueous suspension of non-porous solid particles is studied. The experim ents are carried out as function of the concentration of the colloidal particles at constant temperature. The aqueous suspensions are prepar ed with three kinds of particles of different size (radius r approxima te to 500, 200, 5 nm). It is found that the resonance frequency is ind ependent of the concentration of the colloidal particles with r approx imate to 500 and 200 nm. It has approximately the value of the resonan ce frequency of the fluid medium in the absence of the colloidal parti cles. For the colloidal particles with r approximate to 5 nm a small c hange of the resonance frequency with the concentration of the colloid al particles is observed. An attempt is made to rationalize this findi ng. The observation could be of importance to practical applications o f the quartz crystal microbalance as a sensor in fluids.