Title: Microfluidic flowmeter based on a liquid crystal-filled nested capillary
Authors: Zhe Wang, Arun Kumar Mallik, Fangfang Wei, Zhuochen Wang, Anuradha Rout, Rayhan Habib Jibon, Qiang Wu, and Yuliya Semenova
Journal: Communications Engineering (Nature)
Link to full paper: https://www.nature.com/articles/s44172-024-00202-7
What is this paper all about?
Microfluidics is the study of how to move very small amounts of fluids, about the size of a micrometer, which is much smaller than a human hair. Researchers are creating small devices that can fit in your hand, and these can help with tasks like detecting biological signals, observing chemical reactions, and sorting tiny particles.
A key part of these small fluid systems is a liquid flow sensor. This sensor measures how quickly small amounts of liquid move. Because these systems are tiny, measuring the flow directly is not possible, but there are different methods to estimate it, each with its own advantages and disadvantages. Many flow sensors available today use thermal or mechanical methods and tend to be large and costly, making it difficult to use them in microfluidic systems.
In our study, we developed a new flow sensor that uses light to measure flow rates. This sensor is built with a special design called a nested capillary, which is a small tube filled with a liquid crystal. When liquid or air flows through this tube, it changes the temperature of the liquid crystal and alters the color of the light passing through it.
Nested capillary-based flow sensor and laboratory setup for flow rate measurements
We first analyzed how to connect a thin optical fibre to our nested capillary to capture as much light as possible. Then, we used computer simulations to fine-tune the sizes of the capillaries to create clear light patterns. Next, we studied how the properties of the liquid crystal affected these light patterns. We also ran simulations to see how the temperature of the liquid crystal changes with the flow of air or liquid. After designing our sensor, we built it and tested how well it functions. We found that as the flow rate increases, the light wavelength shifts in a predictable way.
So what?
Our tests showed the sensor is very sensitive, especially at lower flow rates. Our new sensor is small, very sensitive, and has potential uses in detecting of movement of different gases and liquids in real-time. While the sensor shows promise, we face challenges, such as keeping it at a stable temperature and making it more mechanically stable. We also want to create an easier, more affordable way to read its results. This technology could advance how we monitor tiny fluid movements or gas leaks in various applications. For example, to monitor and control the flow of chemicals in chemical processing plants, oil and gas in pipelines, water and wastewater in water treatment plants, air in HVAC systems, liquids in food and beverage production facilities, liquids and gases in pharmaceutical production facilities, and even in medical settings for injecting of fluids directly into the blood stream through a vein in the arm of a patient.
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