The application of the droplet quartz crystal microbalance (QCM) to the measurement of viscosity for industrial oils is reported. In this approach a small-volume droplet of fluid is investigated via its influence on the resonant frequency of a quartz oscillator. The droplet QCM viscosity response is investigated for a selection of industrial oils, including commercial automotive lubricants, heavy fuel oils, calibration oils and used automotive lubricating oils. This approach shows significant analytical promise for distinguishing between heavy fuel oils dyed to indicate their duty status. It is also demonstrated that lubricating oils aged in engine tests exhibit an enhanced QCM viscosity response than accepted viscosity measurements would otherwise indicate. The locus at which the viscosity response saturates due to violation of the small loading approximation (extreme viscosities) is identified and found to be qualitatively consistent with established equivalent circuit models. The identification of commercial lubricating oils is observed to be unreliable on the basis of viscosity response alone.

No abstract