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QCM-D is a sensitive analytical device that measures changes in adsorbed mass by detecting associated changes in the resonance frequency of an oscillating quartz crystal. Because the QC resonant frequency depends on the total mass which must be moved by the vibrating crystal, QCM measures both adsorbed analytes and any associated solvent which is firmly coupled to the analytes.

This method of sensing is fundamentally different from OWLS or ellipsometry, in that it measures a physical effect caused by adsorption, not an optical change. Indeed, since optical techniques measure "non-solvent" molecules, they report an amount that is effectively a "dry mass" — QCM, however, reports a "wet mass" corresponding to the analyte and entrained solvent.

The "dissipation monitoring" part is a simple but powerful technique. The high-frequency driver that makes the crystal oscillate is periodically turned off, and the oscillations damp out. The adsorbed layer absorbs some of the crystal energy, and transmits it to the solvent. A more rigid layer damps the oscillations more slowly than a flexible or viscous layer, so the time required for the "ringing" to decay is an indication of the viscoelasticity of the adlayer. This can be used to quantify phenomena such as swelling and hydration, polymerization, annealing of films, etc.

In addition, Q-sense offers seven different interchangeable sensor modulesΔ, including modules to support high-temperature or vacuum studies, open or optical flow cells, and cells designed for electrochemical studies.

The instrument we have is the Q-Sense E4.

PROTOCOL FOR QCM-D EXPERIMENTS: Latest experimental protocol, revised 11/5/2014Δ


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