Microfluidic on chip viscometers

We present the design and the process of fabrication of micromachined capillary on chip rheometers which have performed wall shear stress and shear rate measurements on silicon oil and ethanol-based nanofluids. The originality of these devices comes from the fact that local pressure drop measurements are performed inside the microchannels. Thus, the advantage over existing microviscometers is that they can be used with the fluid under test alone; no reference fluid nor posttreatment of the data are needed. Each on chip viscometer consists of anodically bonded silicon-Pyrex derivative microchannels equipped with local probes. The anodic bonding allows to reach relatively high pressure levels (up to approximately 10 bars) in the channels, and a broad range of shear stress and shear rate values is attainable. Dielectrophoretic and electrorheological effects can be highlighted by employing alternate microstripe electrodes patterned onto the inner side of the Pyrex wall.