Foundations and Applications of Miniaturized Rheometers

With progressing possibilities in device miniaturization, sensors for online-monitoring become increasingly attractive for industrial and related applications. Examples are the monitoring of fluids in production processes used in the food industry and the observation of the deterioration of lubricants, e.g., in internal combustion engines. For many of these applications, monitoring of the rheological state of a fluid is of crucial importance. Conventional rheometers or viscometers, however, are bulky, expensive or they involve elaborate testing (or sampling) procedures. Each of these factors hampers the broad introduction of conventional instrumentation in online-monitoring systems. The aforementioned progress in micro-fabrication technologies and in particular in microsystems technology (MST), which enables the batch fabrication of miniaturized devices, seems to provide an opportunity to overcome the disadvantages associated with conventional rheometers. The operation principles of potentially suitable miniaturized rheometric devices are often related with classical principles but in general they probe the liquid sample in a different rheological regime, e.g., in terms of applied frequencies and shear rates. This dependence on the measurement parameters is also known and well-studied for different classical measurement methods but the parameter regimes covered by conventional equipment are commonly far away from those covered by miniaturized sensors, which often makes the measurement results scarcely comparable. Initial research on this topic showed that this specific "microrheological" behavior on the one hand needs to be considered in the design of miniaturized rheometric devices and in the interpretation of their output signals, i.e. the measurement result. On the other hand, certain rheological effects, which are detected by miniaturized devices, open new possibilities for monitoring applications in particular. The aim of the project is to further investigate on the particular rheological behavior of different miniaturized viscosity sensor principles in order to develop a full understanding of different device principles in different applications and for different categories of liquids. At the same time the promising concept of a micromachined cantilever sensor shall be exploited further. The results shall enable the efficient application of miniaturized sensors in online monitoring systems.