Simultaneous measurement of microscale fluid viscosity, temperature, and velocity fields by tracking Janus particle on microparticle image velocimetry

Abstract

Multifunctional sensing capability enables a comprehensive understanding of the unknown target to be measured. Given that fluid viscosity, temperature, and velocity fields are usually coupled parameters in a system, simultaneous measurement of the three environmental factors can prevent cross-talk and improve reliability. However, the task is apparently challenging because of the microscale targets. A technique combining microparticle image velocimetry and Janus particles was developed in this study to address such demand. With the rotational diffusivity and particle trajectories measured by the proposed technique and an empirical water-based viscosity-temperature relationship, the three unknown variables in a microfluidic environment were solved. The blinking frequency was derived using the Hilbert Huang Transform. Compared with those in a static and uniform temperature field, the measured data had good agreement with the predicted values. However, the agreement was impaired when the heating rate exceeded 0.34 °C/s. The optimal temperature range was found between 10 °C and 40 °C in the water-based solution. For a steady-state and nonuniform temperature field, two-dimensional (2D) numerical simulations of three linear temperature gradients were also studied. Results showed that the deviation increased as the temperature gradient increased or was near the low-temperature region. The same procedure was eventually applied to a real thermophoretic flow induced by an IR laser in a microchip. The 2D fluid viscosity, temperature, and velocity fields in the microchip were successfully obtained by tracking 10 particles. The potential of the approach provides insight into understanding some microfluidic applications with mild changes in temperature or creeping flow. This study combined µPIV with Janus particles to achieve simultaneous measurement of 2D microscale fluid viscosity, temperature, and velocity fields. By simply tracking the particles, particle trajectories and blinking signal were obtained. Both parameters provided sophisticated information of particle velocity and rotational diffusivity. With the information, the viscosity and temperature were hence derived from the empirical viscosity–temperature relationship and the Stokes-Einstein-Debye relation. The velocity was derived alone based on the conventional cross-correlation algorithm. • Using Janus particles as tracers to provide dynamic information of blinking signal and trajectories. • Simultaneous measurement of whole field fluid viscosity, temperature, and velocity at the microscale. • Extraction of the frequency spectrum out of blinking signal by Hilbert Huang Transform. • A measurable temperature range between 10 °C and 40 °C.