Department of Physics, Durham University, Durham, UK.
Analyst. 2017 May 2;142(9):1492-1498. doi: 10.1039/c6an02674e.
Many industrial and technological applications require precise determination of the viscosity and density of liquids. Such measurements can be time consuming and often require sampling substantial amounts of the liquid. 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. Here we present a new approach able to simultaneously quantify both the density and the viscosity of microliters of liquids. The method, based solely on the measurement of two characteristic frequencies of an immersed microcantilever, is completely independent of the choice of a cantilever. We derive analytical expressions for the liquid's density and viscosity and validate our approach with several simple liquids and different cantilevers. 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. However, the results become increasingly dependent on the cantilever geometry as the frequency-dependent nature of the liquid's viscosity becomes more significant.
许多工业和技术应用都需要精确测定液体的粘度和密度。此类测量通常既耗时又费力，而且往往需要采集大量的液体样本。微悬臂梁的使用在一定程度上可以解决这些问题，但大多数现有的方法都依赖于悬臂梁的特定几何形状和特性，这使得简单、精确的测量变得困难。在这里，我们提出了一种新的方法，能够同时定量测量微升液体的密度和粘度。该方法仅基于浸入式微悬臂梁的两个特征频率的测量，完全不依赖于悬臂梁的选择。我们推导出了液体密度和粘度的解析表达式，并通过几种简单的液体和不同的悬臂梁验证了我们的方法。将我们的模型应用于非牛顿流体表明，与从标准流变仪获得的测量值相比，计算出的粘度非常稳定。然而，当液体粘度的频率依赖性变得更加显著时，结果对悬臂梁几何形状的依赖性越来越大。
