Contact mechanics studies with the quartz crystal microbalance

A quartz crystal microbalance (QCM) is used to measure the contact area between a gold-coated quartz crystal and a low-modulus elastic solid. When combined with an appropriate contact mechanics analysis, such as the well-known method of Johnson, Kendall, and Roberts, quantitative information about the adhesion of the elastic solid to the electrode surface of the quartz crystal can be obtained. We use a hemispherical, elastic gel to demonstrate that the QCM can be used to acquire contact area information directly, without visually monitoring the area of contact between the gel and the electrode surface. Provided that the area of contact is confined to the central portions of the gold electrode, a linear relationship is observed between the crystal's resonant frequency and the gel/electrode contact area. The coefficient describing this linear relationship depends on the viscoelastic properties of the gel. A simple expression for this coefficient is derived.