Highlight June 2007: Cavitation in a confined environment: potential applications in microfluidics

Cavitation bubbles are well-known to be very aggressive and destructive. This results from the fact that they concentrate the energy of the liquid during their shrinkage and from their ability to focus fluid flows to very small scales.

We investigate here a new range of applications of cavitation bubbles in a microfluidic context, either in a narrow gap or in a microsystem. We first study cavitation phenomena in a confined environment: a single bubble (10-20 μs lifetime) is created in the center of a 20-μm and 1-mm wide channel. We observe a purely radial and symmetric flow. The bubble dynamics borrows much from a 2D Rayleigh model and gives a planar flow characterized with a high Re number (> 500).




Dynamics of a single cavitation bubble created in a microfluidic confinement recorded using a 10⁶ frames/s Shimadzu camera. From left to right; in a 2D boundary free liquid; close to a rigid wall; in a microchannel (150 μm width); in a triangular chamber (200 μm side); in a square chamber ( 200 μm side).

Cavitation bubbles created in a microfluidic system close to microstructures, e.g., a wall, in a microchannel or in a microchamber, give interesting flow profiles. We observe a great influence of the boundaries on the bubble collapse: strong jets develop towards the rigid surface(s) to give an asymmetric flow that ends up as two counter vortices.

These preliminary experiments have demonstrated the potential of cavitation bubbles to solve a few issues encountered in microfluidics such as pumping or mixing liquids providing appropriate design of the microfluidic structures.

More details about this work can be found in Controlled cavitation in microfluidics systems, by Ed Zwaan, Séverine Le Gac, Kinko Tsuji and Claus-Dieter Ohl, Phys. Rev. Let., 98, 254501, 2007.