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Mixing in microfluidics

This topic corresponds to my transition towards microfluidics. This work was done through two collaborations, with P. tabeling from ESPCI and with J. Delaire from ENS-Cachan.

Related papers can be dowloaded at the bottom of this page.
Mixing in a microfluidic system and spatio-temporal resonances
in collaboration with A. Dodge and P. Tabeling - ESPCI

In this work we concentrate on a particular micromixer that exploits chaotic trajectories to achieve mixing. The micromixer we consider here is a cross-channel intersection, in which a main stream is perturbed by an oscillatory flow, driven by an external source. Depending on the amplitude and frequency of the oscillatory flow, one obtains wavy and chaotic regimes, reminiscent of a tendril-whorl mapping. The chaotic states, in which material lines are stretched and folded, favour mixing. A
spatiotemporal resonance phenomenon, in which the material-line deformation is transient, is shown. An experiment using soft lithography and integrated valves, in which the resonant states are revealed, is described. From a practical viewpoint, the cross-channel micromixer offers a variety of regimes, which can be exploited to mix fluids or separate particles of different sizes. In the context of microsystems, it can be viewed as a ‘smart’ elementary system.

Papers : from 2004 to 2005

A novel microfluidic flow-injection analysis device with fluorescence detection for cation sensing. Application to potassium
in collaboration with S. Desportes and J. Delaire - ENS-Cachan

A microfabricated device has been developed for fluorimetric detection of potassium ions without previous separation. It is based on use of a fluorescent molecular sensor, calix–bodipy, specially designed to be sensitive to and selective for the target ion. The device is essentially made of a Y-shape microchannel moulded in PDMS fixed on a glass substrate. A passive mixer is used for mixing the reactant and the analyte. The optical detection arrangement uses two optical fibres, one for excitation by a lightemitting diode, the other for collection of the fluorescence.This system enabled the flow-injection analysis of the concentration of potassium ions in aqueous solutions with a detection limit of 0.5 mmol L−1 and without interference with sodium ions. A calibration plot was constructed using potassium standard solutions in the range 0–16 mmol L−1,
and was used for the determination of the potassium content of a pharmaceutical pill.

Paper : 2007

Mixing Regime :

YouTube Video

Resonant regime :

YouTube Video