A fast microfluidic mixer based on acoustically driven sidewall-trapped microbubbles

  • Daniel Ahmed
  • Xiaole Mao
  • Bala Krishna Juluri
  • Tony Jun HuangEmail author
Short Communication


Due to the low Reynolds number associated with microscale fluid flow, it is difficult to rapidly and homogenously mix two fluids. In this letter, we report a fast and homogenized mixing device through the use of a bubble-based microfluidic structure. This micromixing device worked by trapping air bubbles within the pre-designed grooves on the sidewalls of the channel. When acoustically driven, the membranes (liquid/air interfaces) of these trapped bubbles started to oscillate. The bubble oscillation resulted in a microstreaming phenomenon—strong pressure and velocity fluctuations in the bulk liquid, thus giving rise to fast and homogenized mixing of two side-by-side flowing fluids. The performance of the mixer was characterized by mixing deionized water and ink at different flow rates. The mixing time was measured to be as small as 120 ms.


Microfluidics Rapid mixing Bubble-trap Acoustic microstreaming 



Authors thank Madineh Sarvestani, Thomas Walker, and Aitan Lawit for helpful discussion and Tristan Tabouillot for assistance in experiments. This research was supported by National Science Foundation (ECCS-0824183 and ECCS-0801922) and the Penn State Center for Nanoscale Science (MRSEC). Components of this work were conducted at the Penn State node of the NSF-funded National Nanotechnology Infrastructure Network.

Supplementary material

10404_2009_444_MOESM1_ESM.doc (2.5 mb)
Fig. S1 The sidewall grooves were filled with fluid (no bubbles were trapped). (a) Laminar flow of deionized water and ink in the absence of acoustic waves. (b) Laminar flow of deionized water and ink in the presence of acoustic waves. (DOC 2607 kb)
10404_2009_444_MOESM2_ESM.mpg (2.5 mb)
The video shows the bubbles were trapped when deionized water was injected into one inlet at a flow rate of 3 µl/min. As the fluid passed through the pre-designed grooves on the sidewall of the channel, air bubbles were trapped
10404_2009_444_MOESM3_ESM.mpg (3 mb)
The video shows the membrane of an air bubble oscillating when acoustically excited at a natural frequency of 81.4 kHz
10404_2009_444_MOESM4_ESM.mpg (1.1 mb)
The video shows the mixing effect of ink and water as the bubbles were acoustically excited at their natural frequency. Vigorous streaming resulted in homogenous mixing right after the fluids passing the first two bubbles. The combined flow rate was 12 µl/min


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Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • Daniel Ahmed
    • 1
  • Xiaole Mao
    • 1
    • 2
  • Bala Krishna Juluri
    • 1
  • Tony Jun Huang
    • 1
    • 2
    Email author
  1. 1.Department of Engineering Science and MechanicsPennsylvania State UniversityUniversity ParkUSA
  2. 2.Department of BioengineeringPennsylvania State UniversityUniversity ParkUSA

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