Abstract
In the present work, an integrated optofluidic chip for fluid viscosity measurements in the range from 1 mPa·s to 100 mPa·s is proposed. The device allows the use of small sample volumes (<1 µL) and the measurement of viscosity as a function of temperature. Thanks to the precise control of the force exerted on dielectric spheres by optical beams, the viscosity of fluids is assessed by comparing the experimentally observed movement of dielectric beads produced by the optical forces with that expected by numerical calculations. The chip and the developed technique are validated by analyzing several fluids, such as Milli-Q water, ethanol and water–glycerol mixtures. The results show a good agreement between the experimental values and those reported in the literature. The extremely reduced volume of the sample required and the high flexibility of this technique make it a good candidate for measuring a wide range of viscosity values as well as for the analysis of nonlinear viscosity in complex fluids.
Highlights
Microrheology recently emerged among the techniques used to characterize the mechanical properties of soft materials or fluids, thanks to the possibility to study the response of samples at the molecular level
Optical forces are a natural candidate for microrheology, as they can be finely controlled and integrated in microfluidic devices
An integrated optofluidic chip is presented in this work that allows the measurement of fluid viscosity, and very low fluid sample consumption is achieved by using micropipette injection
Summary
Microrheology recently emerged among the techniques used to characterize the mechanical properties of soft materials or fluids, thanks to the possibility to study the response of samples at the molecular level. The possibility to force the probe movements opens the way both to the measurement of high-viscosity samples, where the detection of the Brownian motion of the probe could be extremely challenging, and to the study of the material response to strong and impulsive stresses. Such techniques generally apply optical or magnetic forces to a probe (or a multitude of probes) inside the material without affecting it directly [5,6,7]. Optical forces are a natural candidate for microrheology, as they can be finely controlled and integrated in microfluidic devices
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