Design of microfluidic viscometer based on pressure estimation

Abstract

Accurate measurement of viscosity using small samples is important considering the role of viscosity in the dynamics of physical, chemical, and biological systems. The microfluidic viscometer proposed in previous studies can measure the viscosity of fluids by estimating the pressure between samples and reference flows from the interfacial width. Therefore, accurate detection of the interfacial width is important in terms of the performance of a viscometer. We investigate flow behaviors in the microfluidic viscometer depending on their shape. In the simulation results, sample and reference flows are accelerated around the sharp corners of the viscometer. Flow disturbance around corners results in regions with a high-shear rate. The area of the high-shear region becomes wider as the confluence angle increases. To experimentally check the variation of flow conditions depending on the confluence angle, the flow rate and interfacial width were measured in a microfluidic viscometer designed using mold fabricated with a 3D printer. The width ratios obtained from the experiment results are varied depending on the confluence angle of the viscometer. This indicates that a high-shear region around a sharp corner can lead to inaccurate measurement of the microfluidic viscometer. To reduce the high-shear regions, the distributions of the shear rate were investigated depending on the degree of the rounded corners. A region with a high-shear rate is significantly decreased by increasing the radius of curvature. From the results, a microfluidic viscometer with a confluence angle of 30° and rounded curves is suitable for measuring the viscosity based on an estimation of the pressure. By using the selected design of the microfluidic viscometer, the viscosity of a blood sample is reasonably measured depending on the shear rate. A microfluidic viscometer with a suitable design can be utilized as a viscometer with significant advantages in terms of mobility and ease of operation by combining it with mobile sensing equipment.