Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) is a real-time, nanoscale technique for analyzing surface phenomena including thin film formation, interactions and reactions.
A QCM sensor consists of a thin quartz disc sandwiched between a pair of electrodes. The sensor can be excited to oscillate at its resonance frequency by the application of an alternating voltage. The resonance frequency depends on the total oscillating mass of the sensor and sensor surface adhering layers, including coupled water. The frequency decreases when a thin film is attached to the sensor. If the film is thin and rigid the decrease in frequency is proportional to the mass of the film. In this way, the QCM operates as a very sensitive balance. Unlike all other QCMs, QCM-D monitors the frequency and energy dissipation response of the freely oscillating sensor, thus generating results more accurately and faster.
Common applications of QCM-D include measurements of proteins, polymers, surfactants and cells interacting with surfaces in liquid.
The amount of water in an adsorbed film can be as high as 95% depending on the kind of molecule and the type of surface you are studying.
If some elongated molecules adsorb flat on a surface, little water will be coupled to the molecules. However, if they adsorb standing up, lots of water will be coupled. The kinetics of structural changes and mass changes involved are obtained simultaneously with QCM-D.