Capillary-based micro-optofluidic viscometer

In this study, a capillary-based micro-optofluidic viscometer, which is capable of measuring dynamic viscosity in a range of with only a small volume of liquid (26 µl) in just a few seconds (less than 15 s for most of the samples used) with an acceptable accuracy (99.56%), has been designed, fabricated, and tested. This device consists of two different parts, namely a poly(methyl methacrylate) (PMMA) microfluidic chip and an electro-optical detection system. The viscometer determines viscosity by measuring the time that the liquid travels between two specific points of a rectangular microchannel. The microchannel has been micro-milled on a PMMA substrate, which has been bonded to another PMMA sheet. The fluid flow inside the microfluidic chip has been created by the capillary driven flow; hence, there is no need for any external devices to generate fluid flow. The resolution of this microviscometer is approximately 0.001 mPa s. An ADC circuit has been added to the electro-optical detection system, which is an optically-activated stopwatch circuit, to enhance accuracy, sensitivity, resolution, and to make this viscosity measurement device applicable and efficient for a wide range of applications. This integrated microviscometer automatically notices entry of liquid and completion of the experiment, and finally gives the result. In this study, only Newtonian fluids were tested via this microviscometer, but this device is also capable of measuring non-Newtonian liquids. This portable microviscometer has applications in different fields such as point-of-care diagnosis, chemical and food industries, pharmaceutical industries, research laboratories, etc.