Biomedical subjects

Jean-Baptiste Salmon

Publications and source records attributed to Jean-Baptiste Salmon.

8 recordsLinked to original sources

PubMed2006

Viscosimeter on a microfluidic chip.

In this work, a viscosimeter implemented on a microfluidic chip is presented. The physical principle of this system is to use laminar parallel flows in a microfluidic channel. The fluid to be studied flows side by side with a reference fluid of known viscosity. By using optical microscopy, the shape of the interface between both fluids can be determined. Knowing the flow rates of the two liquids and the geometrical features of the channel, the mean shear rate sustained by the fluid and its viscosity can thus be computed. Accurate and precise measurements of the viscosity as a function of the shear rate can be made using less than 300 microL of fluid. Several complex fluids are tested with viscosities ranging from 10(-)(3) to 70 Pa.s.

Journal Article↗

PubMed2006

X-ray microfocussing combined with microfluidics for on-chip X-ray scattering measurements.

This work describes the fabrication of thin microfluidic devices in Kapton (polyimide). These chips are well-suited to perform X-ray scattering experiments using intense microfocussed beams, as Kapton is both relatively resistant to the high intensities generated by a synchrotron, and almost transparent to X-rays. We show networks of microchannels obtained using laser ablation of Kapton films, and we also present a simple way to perform fusion bonding between two Kapton films. The possibilities offered using such devices are illustrated with X-ray scattering experiments. These experiments demonstrate that structural measurements in the 1 A-20 nm range can be obtained with spatial resolutions of a few microns in a microchannel.

Microarray Analysis↗

PubMed2005

An approach to extract rate constants from reaction--diffusion dynamics in a microchannel.

A theoretical model is proposed to extract rate constants of second-order chemical reactions down to the millisecond time scale from the observation of reaction-diffusion processes in a microchannel. We validate this theoretical approach by examining an appropriate model reaction. The measured rate constant is in excellent agreement with this obtained from nuclear magnetic resonance experiments.

Coumarins↗

PubMed2004

Observation of droplet size oscillations in a two-phase fluid under shear flow.

Experimental observations of droplet size sustained oscillations are reported in a two-phase flow between a lamellar and a sponge phase. Under shear flow, this system presents two different steady states made of monodisperse multilamellar droplets, separated by a shear-thinning transition. At low and high shear rates, the droplet size results from a balance between surface tension and viscous stress, whereas for intermediate shear rates it becomes a periodic function of time. A possible mechanism for such kinds of oscillations is discussed.

Journal Article↗

PubMed2003

Shear banding in a lyotropic lamellar phase. I. Time-averaged velocity profiles.

Using velocity profile measurements based on dynamic light scattering and coupled to structural and rheological measurements in a Couette cell, we present evidences for a shear banding scenario in the shear flow of the onion texture of a lyotropic lamellar phase. Time-averaged measurements clearly show the presence of structural shear banding in the vicinity of a shear-induced transition, associated with the nucleation and growth of a highly sheared band in the flow. Our experiments also reveal the presence of slip at the walls of the Couette cell. Using a simple mechanical approach, we demonstrate that our data confirm the classical assumption of the shear banding picture, in which the interface between bands lies at a given stress sigma(*). We also outline the presence of large temporal fluctuations of the flow field, which are the subject of the second part of this paper [Salmon et al., Phys. Rev. E 68, 051504 (2003)].

Journal Article↗

PubMed2003

Shear banding in a lyotropic lamellar phase. II. Temporal fluctuations.

We analyze the temporal fluctuations of the flow field associated with a shear-induced transition in a lyotropic lamellar phase: the layering transition of the onion texture. In the first part of this work [Salmon et al., Phys. Rev. E 68, 051503 (2003)], we have evidenced banded flows at the onset of this shear-induced transition which are well accounted for by the classical picture of shear banding. In the present paper, we focus on the temporal fluctuations of the flow field recorded in the coexistence domain. These striking dynamics are very slow (100-1000 s) and cannot be due to external mechanical noise. Using velocimetry coupled to structural measurements, we show that these fluctuations are due to a motion of the interface separating the two differently sheared bands. Such a motion seems to be governed by the fluctuations of sigma(*), the local stress at the interface between the two bands. Our results thus provide more evidence for the relevance of the classical mechanical approach of shear banding even if the mechanism leading to the fluctuations of sigma(*) remains unclear.

Journal Article↗

PubMed2003

Velocity profiles in shear-banding wormlike micelles.

Using dynamic light scattering in heterodyne mode, we measure velocity profiles in a much studied system of wormlike micelles (CPCl/NaSal) known to exhibit both shear-banding and stress plateau behavior. Our data provide evidence for the simplest shear-banding scenario, according to which the effective viscosity drop in the system is due to the nucleation and growth of a highly sheared band in the gap, whose thickness linearly increases with the imposed shear rate. We discuss various details of the velocity profiles in all the regions of the flow curve and emphasize the complex, non-Newtonian nature of the flow in the highly sheared band.

Journal Article↗

PubMed2002

Dynamical behavior of a complex fluid near an out-of-equilibrium transition: approaching simple rheological chaos.

We report here an extensive study of sustained oscillations of the viscosity of a complex fluid near an out-of-equilibrium transition. Using well defined protocols, we perform rheological measurements of the onion texture near a layering transition in a Couette flow. This complex fluid exhibits sustained oscillations of the viscosity, on a large time scale (500 s) at controlled stress. These oscillations are directly correlated to an oscillating microstructural change of the texture of the fluid. We observe a great diversity of dynamical behavior and show that there is a coupling with spatial effects in the inverted Delta v direction. This is in agreement with a careful analysis of the temporal series of the viscosity with the dynamical system theory. This analysis indicates that the observed dynamical responses do not strictly correspond to three-dimensional chaotic states, probably because some spatiotemporal effects are present and are likely to play an important role.

Journal Article↗