Abstract
Particle behavior in viscoelastic fluids has attracted considerable attention in recent years. In viscoelastic fluids, as opposed to Newtonian fluids, particle focusing can be simply realized in a microchannel without any external forces or complex structures. In this study, a polydimethylsiloxane (PDMS) microchannel with a rhombic cross-sectional shape was fabricated to experimentally investigate the behavior of inertial and elasto-inertial particles. Particle migration and behavior in Newtonian and non-Newtonian fluids were compared with respect to the flow rate and particle size to investigate their effect on the particle focusing position and focusing width. The PDMS rhombic microchannel was fabricated using basic microelectromechanical systems (MEMS) processes. The experimental results showed that single-line particle focusing was formed along the centerline of the microchannel in the non-Newtonian fluid, unlike the double-line particle focusing in the Newtonian fluid over a wide range of flow rates. Numerical simulation using the same flow conditions as in the experiments revealed that the particles suspended in the channel tend to drift toward the center of the channel owing to the negative net force throughout the cross-sectional area. This supports the experimental observation that the viscoelastic fluid in the rhombic microchannel significantly influences particle migration toward the channel center without any external force owing to coupling between the inertia and elasticity.
Highlights
Particle manipulation in microfluidic channels has been widely applied in the biological, medical, chemical, and environmental fields owing to their capacity for high efficiency, high accuracy, and fast processing with the additional advantages of low cost and reduced sample consumption [1,2,3,4,5]
The results showed that single-line particle focusing occurred along the centerline of the microchannel in the non-Newtonian fluid, unlike the double-line particle focusing in the Newtonian fluid over a wide range of flow rates
The typical fabrication processes are as follows: (i) A thin film of Si3N4 with a layer thickness of 1000 Å was deposited on a (100) single-crystal Si wafer using low-pressure chemical vapor deposition (LPCVD) and patterned by photolithography and reactive ion etching (RIE); (ii) the Si wafer was anisotropically etched with KOH solution at 70 ◦C; (iii) a PDMS (Dow Corning, Midland, MI, USA) microchannel was replicated from a polystyrene (PS) mold created from the Si microchannel; (iv) the PDMS mold was replicated from the Si master; (v) the PDMS microchannel and the PDMS mold were self-aligned and bonded by O2 plasma
Summary
Particle manipulation in microfluidic channels has been widely applied in the biological, medical, chemical, and environmental fields owing to their capacity for high efficiency, high accuracy, and fast processing with the additional advantages of low cost and reduced sample consumption [1,2,3,4,5]. Inertial microfluidics as a representative passive method has been extensively studied and employed to accomplish particle ordering, focusing, and separation [6,7,8] in a Newtonian fluid such as deionized (DI) water and phosphate-buffered saline (PBS) solution. This method has certain advantages such as that an external force is not required, the device is easy to operate, and the microchannel structure is simple, the disadvantage is that particles may be focused in multiple linear streams (rather than a single stream) because of the inertial forces in a Newtonian fluid. Particle behavior in non-Newtonian fluids is affected by fluid elasticity in addition to inertial forces, particle migration in viscoelastic fluids has given rise to highly interesting and useful phenomena [11]
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