Rapid sedimentation of microparticles by vertically asymmetric acoustofluidics in an equilateral triangular channel

Abstract

The ability to settle particles in a fluid has a significant impact on many applications in fields like biology, chemistry, environment, and industrial processing. Here, we set up an acoustofluidics framework, based on an equilateral-triangular-channel design, which can generate vertically asymmetric acoustic pressure profiles and can result in unidirectionally downward acoustic radiation force and acoustic streaming-induced drag force on the pressure nodal plane, enabling rapid agglomeration and sedimentation of microparticles toward the channel wall. This approach is verified in an acoustofluidic device, mainly composed of an equilateral triangular glass capillary (with outer and inner side lengths of 2 and 1 mm, respectively) and two piezoelectric transducers (15 × 1.4 × 2 mm3), both experimentally and numerically and a good agreement is obtained. Specifically, ultrasound enhanced sedimentation of 10 μm polystyrene particles was used to demonstrate the efficiency of the system, which shows that, with the additional acoustic force fields, the acoustofluidic resonator had much higher sedimentation efficiency in comparison to the gravity-induced sedimentation in a fluid (which is about 7 min). The ultrasound enhanced settling efficiency (i.e., the settling time) in such a system is strongly dependent on the pressure magnitudes and the configuration of the acoustofluidic device. It was demonstrated that, at a driving voltage of 25 Vpp, the present device enables settling of 95% of the microparticles to the channel wall within 30 s and 100% at about 1 min.