การพัฒนาระบบไมโครฟลูอิดิกส์เพื่อหาค่าความหนืดของของไหลโดยวิธีการโฟกัสอนุภาคแบบเฉื่อย

Abstract

Inertial focusing in microfluidic systems has been increasingly interested recently due to its capability of manipulating and separating particles flowing in microfluidic systems. One of the crucial parameters affecting equilibrium positioning of a particle in the inertial focusing is the carrying fluid’s viscosity. Viscosity of a fluid property that describes resistance to flow of the fluid due to interaction between fluid molecules. Obtaining the fluid viscosity value is of importance in medical and industrial fields. This work proposes applying microfluidics along with inertial focusing insights in determining viscosity of small needed volume fluid by studying the relationship between particle’s equilibrium position in direction perpendicular to the flow and the flow viscosity. In the study, 15 µm polystyrene microspheres were flowed along with propylene glycol and deionized water solution of various concentrations in a 100 µm square cross section microchannel of 4.7 cm long at different fluid flow speeds to study effects of flow parameters on particle’s equilibrium position. Additionally, particle’s trajectory and equilibrium position in particle inertia focusing phenomenon was simulated using COMSOL Multiphysics software with Laminar Flow and Particle Tracing for Fluid Flow module for measuring a change of particle equilibrium position due to changes of fluid viscosity and fluid speed. From the results of the study, it was found experimentally that for the solution concentrations of 0%, 10%, 20%, and 30% and the fluid flow speeds equivalent to 50, 75, 100, and 125 ms/step stepping motor pumping period, the polystyrene particles’ equilibrium positions range from 34.5 - 36.25 µm while the results of the simulations with the same initial conditions yield equilibrium positions in the range of 27.5 -35 µm. The 1-8 µm difference between the real experiment and simulation could stem from the exclusion of interaction between particles in the flow from the simulation. The small amount added surfactant to alleviate particles agglomeration could also affect the effective fluid viscosity.