디지털 홀로그래피 기법을 이용한 미세채널 내부 점탄성 유체에서의 입자 거동 분석
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The lateral migration of microspheres across streamlines induced by elasticity and inertia in circular and square channel flows of viscoelastic fluids was investigated using holographic microscopy technique. Exact particle positions driven by the elasticity of viscoelastic fluids in the channel cross-section were experimentally obtained. The effects of the blockage ratio, flow rate, and shear-thinning property of the viscoelastic fluids on particle migration ware evaluated. In particular, the focusing patterns of microspheres were analyzed under different conditions, namely, dominant inertia, dominant elasticity, and the combined effects of inertia and elasticity. In addition, we propose the focusing number, a non-dimensional parameter, to estimate the focusing state of particles in elasticity-dominant fluids. This parameter can be used to accurately estimate the design parameters, such as rheological properties, channel length, and particle diameter, for microfluidic devices using elasto-migration phenomena. As a practical application, we demonstrated sheath-free vertical concentration and positioning of particles and cells induced by fluid viscoelasticity in a rectangular channel. The high uniformity in depth position and the reduction in cell overlap eliminate out-of-focus blurring and increase detection sensitivity. Additionally, orientational ordering of red blood cells improves the monitoring and counting performance of an optical imaging system. Finally, we demonstrated counting and monitoring of red blood cells flowing in a microchannel using phase-contrast holographic microscopy for quantitative phase imaging.