Issue 21, 2015

Vibrating membrane with discontinuities for rapid and efficient microfluidic mixing

Abstract

This study presents a novel acoustic mixer comprising of a microfabricated silicon nitride membrane with a hole etched through it. We show that the introduction of the through hole leads to extremely fast and homogeneous mixing. When the membrane is immersed in fluid and subjected to acoustic excitation, a strong streaming field in the form of vortices is generated. The vortices are always observed to centre at the hole, pointing to the critical role it has on the streaming field. We hypothesise that the hole introduces a discontinuity to the boundary conditions of the membrane, leading to strong streaming vortices. With numerical simulations, we show that the hole's presence can increase the volume force responsible for driving the streaming field by 2 orders of magnitude, thus supporting our hypothesis. We investigate the mixing performance at different Peclet numbers by varying the flow rates for various devices containing circular, square and rectangular shaped holes of different dimensions. We demonstrate rapid mixing within 3 ms mixing time (90% mixing efficiency at 60 μl min−1 total flow rate, Peclet number equals 8333 ± 3.5%) is possible with the current designs. Finally, we examine the membrane with two circular holes which are covered by air bubbles and compare it to when the membrane is fully immersed. We find that coupling between the holes' vortices occurs only when membrane is immersed; while with the bubble membrane, the upstream hole's vortices can act as a blockage to fluid flow passing it.

Graphical abstract: Vibrating membrane with discontinuities for rapid and efficient microfluidic mixing

Supplementary files

Article information

Article type
Paper
Submitted
17 júl. 2015
Accepted
09 sep. 2015
First published
09 sep. 2015

Lab Chip, 2015,15, 4206-4216

Author version available

Vibrating membrane with discontinuities for rapid and efficient microfluidic mixing

H. V. Phan, M. B. Coşkun, M. Şeşen, G. Pandraud, A. Neild and T. Alan, Lab Chip, 2015, 15, 4206 DOI: 10.1039/C5LC00836K

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