Anisotropic microfluidics and flow monitoring with a microchannel towards soft-matter sensing

Abstract

Flow monitoring of a fluid confined in a regular microchamber has become essential for fundamental studies and applications, resulting in a bloom in microfluidic techniques. The unique properties of anisotropic fluids make it possible to monitor and feedback the flow dynamics without the assistance of additional complicated external devices. Herein, we develop a fantastic microfluidics device with optically anisotropic liquid crystals to reflect the real-time flow rate via analysis of the interference colors and corresponding transmittance spectra of the liquid crystals confined in a judiciously designed microchannel. A linear relationship between the transmission spectral shift rate and the flow rate is initially observed, thereby enabling a fantastic capability to sense the flow rate of the target fluid in a closed chamber or pipeline. The measurement range of flow rate covers 150 nL min⁻¹ to 6500 nL min⁻¹ when the cross-section size of the microchannel is 60 × 10 μm². This range can be efficiently expanded and the performance can be further enhanced by altering the channel size. This work provides a feasible strategy for flow monitoring and other possible dynamic behaviours of fluids by integrating a microfluidic chip with the tested systems, therefore unlocking the long-sought full potential of such non-invasive optical microfluidic techniques in chemical engineering, environmental monitoring, biological medicine, and even microfluidic photonics.