Measuring the viscosity of glycerin solutions in very small samples using Sciospec ISX-3 Impedance Analyzer
Measuring the viscosity of very small sample volumes is of high interest in many fields especially in miniaturized and micro-fluidic systems. This application note describes an approach using the change of the impedance spectrum of a Thickness Shear Mode Resonator in combination with a sophisticated fitting algorithm. The simple setup of the measuring system enables easy integration in existing micro-fluidic settings with almost no adaption. As validation of the Sciospec ISX-3 a comparison to theoretical values and to a commercially available vector network analyzer on the same setup is provided.
The measurement of the viscosity is very well known for sample volumes larger than a couple milliliters. The standard viscometers use either rotating parts, a flow through, a capillary system or falling spheres. This application note describes an example of measuring smaller sample volumes with no need for mechanical parts.
A thickness shear mode resonator (TSM) with a nominal frequency of 9 MHz was connected to the Sciospec ISX-3 by a custom adapter with SMA connectors. Since the sensitivity is highly dependent on the temperature of the sensor chip it was held constant at 25°C with an external temperature controller. The frequency range was set to 8.9 MHz to 9.1 MHz with 1001 linear distributed points. The inter-frequency delay was set to 10 ms, so the quartz system was allowed enough time to adapt to the change in generator frequency. As control fluid a sample of 1.2 ml double distilled Water was added to the sensor. After 5 min of equalization of temperature the impedance spectrum was measured and saved with the Sciospec Impedance Analyzer suite. After thorough rinsing of the TSM chip, this procedure was repeated with 10, 30, 50 and 70 mass-% glycerin solution. All impedance spectra are shown in Fig 1.