MEASUREMENT OF VISCOSITY IN SMALL VOLUMES OF FLUIDS BY TUNING FORK OSCILLATORS

We report on the construction and performance of a home-built viscometer employing a quartz tuning fork resonator as the sensing element. The resulting device allows measuring the viscosity of fluids in volumes as low as 300 mu l, while controlling the temperature between -120 degrees C and 150 degrees C. For non-conducting fluids, bare tuning forks can be used, reaching the accuracy of 1% or better in the whole temperature range. For weakly conducting fluids such as aqueous solutions, an insulating coating of paint is applied, resulting in reduced sensitivity and accuracy. The capabilities and limitations of the viscometer are illustrated on the viscosity measurements of n-hexane (between -90 degrees C and +50 degrees C) and water (between 10 degrees C and 90 degrees C). Improvements regarding performance in conducting liquids and temperature stabilization are discussed.