Micro-evaporators for kinetic exploration of phase diagrams

We use pervaporation-based microfluidic devices to concentrate species in aqueous solutions with spatial and temporal control of the process. Using experiments and modelling, we quantitatively describe the advection-diffusion behavior of the concentration field of various solutions (electrolytes, colloids, etc) and demonstrate the potential of these devices as universal tools for the kinetic exploration of the phases and textures that form upon concentration

Mise en en forme de réseaux 3D de nanoparticules par voie microfluidique et applications aux métamatériaux dans le domaine du visible

Les métamatériaux sont définis comme étant des matériaux artificiels présentant des propriétés exotiques qui modifient la propagation des ondes électromagnétiques. À la fin des années 90, Pendry et al. démontrèrent théoriquement qu'il est possible de générer de tels métamatériaux, grâce à des structures particulières au sein du matériau (le fameux "splitring resonator"). Les métamatériaux sont donc structurés à une échelle inférieure à la longueur d'onde incidente, et décrits par une permittivité et une perméabilité effective. En 2000, Smith et al. fabriquèrent le premier métamatériau mais dans la gamme micro-onde. Les perspectives dans le domaine de l'optique (300800 nm) sont très prometteuses, mais le transfert des technologies utilisées en micro-ondes rencontre des obstacles. Un des défis dans le domaine émergent des métamatériaux est d'assembler à grande échelle des nanoparticules NPs (10-50 nm) en des super-réseaux présentant des propriétés collectives. Des nanostructures tridimensionnelles de matériaux nobles, ayant de fortes réponses plasmoniques, peuvent en effet générer des matériaux aux nouvelles propriétés optiques. Cette thèse fait partie du projet européen METACHEM, dont le but est de fabriquer des métamatériaux dans le domaine de l'infrarouge et du visible, en se basant sur l'utilisation de la nanochimie et de l'assemblage de matériaux. Plus précisément, ce travail de thèse se situe à l'interface entre les groupes de chimie qui synthétisent des nanoparticules en dispersion, et les groupes de caractérisation optique des matériaux. Dans ce travail de thèse, nous utilisons une technique originale la microévaporation basée sur les outils microfluidiques, afin de générer de façon contrôlée des assemblées 3D de nanoparticules (dimensions typiques 1 mm10 m 50 m).AbstractBORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Measurement of the ultrasonic diffusion coefficient in a resonant multiple scattering suspension

We report on frequency-resolved experimental measurements of the ultrasonic diffusivity in the MHz range. By means of robotics, we produced a highly monodisperse suspension made of soft metallic micro-beads randomly-dispersed in a water-based gel-matrix. The measured diffusion coefficient is shown to vary significantly with frequency by more than one order of magnitude that is probably due to the sharp scattering resonances of the metallic particles

Elastic instability in stratified core annular flow

We study experimentally the interfacial instability between a layer of dilute polymer solution and water flowing in a thin capillary. The use of microfluidic devices allows us to observe and quantify in great detail the features of the flow. At low velocities, the flow takes the form of a straight jet, while at high velocities, steady or advected wavy jets are produced. We demonstrate that the transition between these flow regimes is purely elastic -- it is caused by viscoelasticity of the polymer solution only. The linear stability analysis of the flow in the short-wave approximation captures quantitatively the flow diagram. Surprisingly, unstable flows are observed for strong velocities, whereas convected flows are observed for low velocities. We demonstrate that this instability can be used to measure rheological properties of dilute polymer solutions that are difficult to assess otherwise.Comment: 4 pages, 4 figure

Microfluidic device for monitoring catalytic events on armored bubbles

Abstract: A polydimethylsiloxane‐based microfluidic device allows monitoring local oxidation events in organic solvents at the level of an individual air bubble armored with surface‐active low‐surface energy catalytic particles. This new technique permits tunable design of microreactors for gas‐liquid‐solid reactions

Social isolation and incident heart failure hospitalization in older women: Women\u27s health initiative study findings

Background The association of social isolation or lack of social network ties in older adults is unknown. This knowledge gap is important since the risk of heart failure (HF) and social isolation increase with age. The study examines whether social isolation is associated with incident HF in older women, and examines depressive symptoms as a potential mediator and age and race and ethnicity as effect modifiers. Methods and Results This study included 44 174 postmenopausal women of diverse race and ethnicity from the WHI (Women\u27s Health Initiative) study who underwent annual assessment for HF adjudication from baseline enrollment (1993-1998) through 2018. We conducted a mediation analysis to examine depressive symptoms as a potential mediator and further examined effect modification by age and race and ethnicity. Incident HF requiring hospitalization was the main outcome. Social isolation was a composite variable based on marital/partner status, religious ties, and community ties. Depressive symptoms were assessed using CES-D (Center for Epidemiology Studies-Depression). Over a median follow-up of 15.0 years, we analyzed data from 36 457 women, and 2364 (6.5%) incident HF cases occurred; 2510 (6.9%) participants were socially isolated. In multivariable analyses adjusted for sociodemographic, behavioral, clinical, and general health/functioning; socially isolated women had a higher risk of incident HF than nonisolated women (HR, 1.23; 95% CI, 1.08-1.41). Adding depressive symptoms in the model did not change this association (HR, 1.22; 95% CI, 1.07-1.40). Neither race and ethnicity nor age moderated the association between social isolation and incident HF. Conclusions Socially isolated older women are at increased risk for developing HF, independent of traditional HF risk factors. Registration URL: http://www.clinicaltrials.gov; Unique identifier: NCT00000611