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Biomedical subjects

P Tabeling

Publications and source records attributed to P Tabeling.

At least 19 recordsLinked to original sources
PubMed2006

Producing droplets in parallel microfluidic systems.

We study the dynamics of two microfluidic droplets emitters placed in parallel. We observe complex dynamical behavior, including synchronization, quasiperiodicity, and chaos. This dynamics has a considerable impact on the properties of the resulting emulsions: chaotic and quasi-periodic regimes give rise to polydispersed emulsions with poorly controllable characteristics, whereas synchronized regimes generate well-controlled monodispersed emulsions. We derive a dynamical model that reproduces the trends observed in the experiment.

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PubMed2006

Slippage of water past superhydrophobic carbon nanotube forests in microchannels.

We present in this Letter an experimental characterization of liquid flow slippage over superhydrophobic surfaces made of carbon nanotube forests, incorporated in microchannels. We make use of a particle image velocimetry technique to achieve the submicrometric resolution on the flow profile necessary for accurate measurement of the surface hydrodynamic properties. We demonstrate boundary slippage on the Cassie superhydrophobic state, associated with slip lengths of a few microns, while a vanishing slip length is found in the Wenzel state when the liquid impregnates the surface. Varying the lateral roughness scale L of our carbon nanotube forest-based superhydrophobic surfaces, we demonstrate that the slip length varies linearly with L in line with theoretical predictions for slippage on patterned surfaces.

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PubMed2006

Arnold tongues in a microfluidic drop emitter.

The Letter reports an experimental study of microfluidic droplets produced in T junctions and subjected to a local periodic forcing. Synchronized and quasiperiodic regimes--organized into Arnold tongues and devil staircases--are reported for the first time for a system dedicated to drop emission. The nature of the dynamical regime controls the droplet characteristics. These phenomena are mostly controlled by the characteristics of the forcing and the flow conditions.

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PubMed2005

Spatiotemporal resonances in a microfluidic system.

We report on the experimental observation of a spatiotemporal resonance phenomenon, in which a temporal excitation locks with a spatial pattern in an open flow system. The observation is made in a microfluidic system. We obtain the expected regimes--mixing and resonant patterns--in qualitative agreement with the theory. As an application, we realized a dual system particle extraction-micromixer.

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PubMed2005

Improving agglutination tests by working in microfluidic channels.

Latex agglutination tests are used for the diagnosis of diseases in man and animals. They are generally simple, cheap, and do not require sophisticated equipment, nor highly specialized skills. In this Technical Note, we put latex agglutination tests in a microfluidic format. The experiment is performed in PDMS (polydimethylsiloxane) microchannels, using streptavidin-coated superparamagnetic beads and a magnetic field. The target molecule is biotinylated protein A. By taking full advantage of the microfluidic conditions (scaling down of the detection volume and controlled action of the shear flow), we achieved an analytical sensitivity of 10 fmol l(-1)(several hundreds of fg ml(-1)) and a fast response (a few minutes) ; the test is also quantitative. Performances of agglutination tests can thus be improved by orders of magnitude by adapting them to a microfluidic format; this comes in addition to the usual advantages offered by this technology (integration, high throughput etc.).

Agglutination Tests↗
PubMed2005

Aggregation of paramagnetic particles in the presence of a hydrodynamic shear.

We present an experimental study of the aggregation of paramagnetic particles, in the presence of controlled laminar shear flow, conducted in microchannels subjected to an external magnetic field. The microfluidic channels are made of either glass/silicon or polydimethylsiloxane. In ranges of time up to hundreds of seconds, the growth mechanism of the linear chain consists of the accumulation of isolated particles or small clusters onto existing chains, which are all moving at different speeds. In this time regime the chain length increases linearly and has a growth rate that increases as a power law with the shear. At longer times the chain lengths saturate. The Smoluchovski model, which assumes single particle-chain interactions only, closely reproduces the observations both qualitatively and quantitatively. In particular, the evolution of the growth rate of the mean chain length with respect to the shear rate S, predicted as S1/4, is found to be consistent with the experiments.

Journal Article↗
PubMed2004

Chaotic mixing in cross-channel micromixers.

In this article 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.

Complex Mixtures↗
PubMed2004

Spatiotemporal resonances in mixing of open viscous fluids.

In this Letter, we reveal a new dynamical phenomenon, called "spatiotemporal resonance," which is expected to take place in a broad range of viscous, periodically forced, open systems. The observation originates from a numerical and theoretical analysis of a micromixer, and is supported by preliminary experimental observations. The theoretical model nicely matches the numerical results, which again is supported by the experiment. Because of the general nature of the phenomenon, this phenomenon is not limited to microsystems. Because of the resonances, a slight tuning of the control parameters makes the mixer enhance the mixing, or suppress it, enhancing interfacial diffusion instead.

Journal Article↗
PubMed2001

Intermittency and coherent structures in the two-dimensional inverse energy cascade: comparing numerical and laboratory experiments.

We study the internal intermittency in the inverse energy cascade and in the condensation regime of two-dimensional turbulence, using physical and numerical experimental approaches. The analysis confirms that the velocity increments have nearly Gaussian distributions at all scales in the inverse cascade regime; it moreover shows that, in the condensation regime, the probability distribution functions of the velocity increments are non-Gaussian but do not significantly vary with the scale; it follows that one may consider that there is essentially no intermittency (in the usual sense), in the condensation regime. In both regimes, we emphasize that coherent structures (i.e., long-lived vortices) are clearly visible on the vorticity field, and we suggest the non-Gaussianity of the distributions in the condensation regime is due to the presence of a large-scale long-lived structures. The study is supplemented by the analysis of the distribution of energy transfers at various scales.

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PubMed2001

Intermittency of a passive tracer in the inverse energy cascade.

We report an experimental study of the dispersion of a passive tracer in the two-dimensional inverse energy cascade, which shows that a nonintermittent velocity field can sustain a strongly intermittent concentration field. The experiment suggests the exponents of the intermittent concentration field saturate at large orders towards xi(infinity) approximately 1.2. These observations are in excellent agreement with a recent numerical work [A. Celani, A. Lanotte, A. Mazzino, and M. Vergassola, Phys. Rev. Lett. 84, 2385 (2000)] and theoretical expectations [E. Balkovsky and V. Lebedev, Phys. Rev. E 58, 5776 (1998); V. Yakhot, ibid. 55, 329 (1997)].

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PubMed2001

Passive scalar intermittency in low temperature helium flows.

We report new measurements of mixing of passive temperature field in a turbulent flow. The use of low temperature helium gas allows us to span a range of microscale Reynolds number, R(lambda), from 100 to 650. The exponents xi(n) of the temperature structure functions approximately r(xi(n)) are shown to saturate to xi(infinity) approximately 1.45+/-0.1 for the highest orders, n approximately 10. This saturation is a signature of statistics dominated by frontlike structures, the cliffs. Statistics of the cliffs' characteristics are performed, particularly their widths are shown to scale as the Kolmogorov length scale.

Journal Article↗
PubMed2000

Experimental observation of batchelor dispersion of passive tracers

We report the first detailed experimental observation of the Batchelor regime [G. K. Batchelor, J. Fluid. Mech. 5, 113 (1959)], in which a passive scalar is dispersed by a large scale strain, at high Peclet numbers. The observation is performed in a controlled two-dimensional flow, forced at large scale, in conditions where a direct enstrophy cascade develops [J. Paret, M.-C. Jullien, and P. Tabeling, Phys. Rev. Lett. 83, 3418 (1999)]. The expected k(-1) spectrum is observed, along with exponential tails for the distributions of the concentration and concentration increments and logarithmlike behavior for the structure functions. These observations, confirmed by using simulated particles, provide a support to the theory.

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