Part of the difficulty comes from the need to take into account the exact geometry of the cantilever and its mechanical properties to precisely determine its hydrodynamic function. This is usually characterized by the so-called hydrodynamic function of the cantilever, which in turn depends on the rheological properties of the liquid.Įarly developments used significant simplifications such as a spherical model for cantilevers 23 or an inviscid fluid 24–26 resulting in large errors or limited applicability. Developing a suitable model is hence far from trivial, because it requires taking into account the coupling between a vibrating cantilever of a given geometry and the surrounding liquid. Fitting the experimental results with theoretical models yields the rheological parameters of the liquid, but the accuracy of the results depends crucially on the quality of the theoretical model, and the ability to implement it fast and robustly. Measurements effectively quantify changes in the dynamic response of the microcantilever upon immersion into the liquid examined. 11–21 These sensors typically require only small volumes (tens of microlitres) of fluid 22 and are able to determine the viscosity and density simultaneously, 11,12,15,18–20 making them particularly attractive for lab-on-chip-type diagnostic devices. To overcome this limitation, sensors based on microcantilevers have been proposed. Measurement methods based on acoustic waves, 8 tuning forks 9 or microfluidics 10 have made it possible to probe smaller liquid volumes, but the liquid's density and viscosity cannot be measured simultaneously one quantity is needed in order to deduce the other from the experimental data. Standard rheometers can provide accurate viscosity measurements over an extensive range of temperatures and pressures 7 but they require relatively large samples, typically several millilitres or more. 4–6 One of the challenges faced by conventional measurement methods is the need for large volumes of liquid.

Applications range from oil and lubricant characterization in the petroleum industry 1 to chemical engineering, 2 quality control in food science 3 and biomedical research, in particular for the detection and diagnosis of diseases from bodily fluids. Introduction Accurate and rapid determination of the density and viscosity of liquids is central to countless industrial, technological and scientific processes. However, the results become increasingly dependent on the cantilever geometry as the frequency-dependent nature of the liquid's viscosity becomes more significant. Application of our model to non-Newtonian fluids shows that the calculated viscosities are remarkably robust when compared to measurements obtained from a standard rheometer. We derive analytical expressions for the liquid's density and viscosity and validate our approach with several simple liquids and different cantilevers. The method, based solely on the measurement of two characteristic frequencies of an immersed microcantilever, is completely independent of the choice of a cantilever.

Here we present a new approach able to simultaneously quantify both the density and the viscosity of microliters of liquids. These problems can partly be overcome with the use of microcantilevers but most existing methods depend on the specific geometry and properties of the cantilever, which renders simple, accurate measurement difficult. Such measurements can be time consuming and often require sampling substantial amounts of the liquid. Many industrial and technological applications require precise determination of the viscosity and density of liquids.

Foss viscosity meter