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La diffusion de rayons X (RX) est un outil classique pour sonder la matiere de l'echelle atomique (1 A) a l'echelle colloidale (100 nm). Pourtant, il existe a l'heure actuelle tres peu de travaux qui combinent les outils de la microfluidique et les techniques de diffusion des RX. Cette etude decrit la microfabrication de puces microfluidiques en polyimide (Kapton) et la fabrication d'un systeme millifluidique simple a base d'elements en polyimide. Ces systemes sont adaptes pour realiser des mesures de diffusion de RX avec un faisceau intense microfocalise car le Kapton est d'une part, relativement resistant aux fortes intensites generees par un synchrotron et transparent aux rayons X d'autre part. Nous presentons des reseaux de microcanaux obtenus par ablation laser et collage thermique de deux films de Kapton ainsi qu'un dispositif millifluidique permettant de generer des gouttes de maniere tres reguliere. Les possibilites qu'offrent ces deux systemes sont illustrees par des experiences de diffusion RX. La premiere etude consiste a suivre, dans un microcanal, la transition de structure d'un fluide complexe sous cisaillement. La deuxieme permet de sonder la composition et la structure des objets contenus dans des gouttes en ecoulement dans un capillaire en polyimide. Ces experiences montrent que des mesures de structures entre 1 A et 20 nm sont realisables avec une resolution spatiale de quelques microns.

In this paper we report on the influence of different geometric and boundary constraints on nonlocal (spatially inhomogeneous) effects in wormlike micellar systems. In a previous paper, nonlocal effects were observable by measuring the local rheological flow curves of micelles flowing in a microchannel under different pressure drops, which appeared to differ from the flow curve measured using conventional rheometry. Here we show that both the confinement and the boundary conditions can influence those nonlocal effects. The role of the nature of the surface is analyzed in detail using a simple scalar model that incorporates inhomogeneities, which captures the flow behavior in both wide and confined geometries. This leads to an estimate for the nonlocal "diffusion" coefficient (i.e., the shear curvature viscosity) which corresponds to a characteristic length from 1 to 10 microm.

This work aims at evaluating a new surfactant based viscoelastic fluid for Chemical EOR applications. The surfactant based fluid exhibits a viscous phase at low concentration and high temperature, useful for improving oil recovery. The viscoelastic fluid is induced by wormlike micelles formed by self-assembled surfactants. The phase diagram of the surfactant in pure water was established using a pervaporation-based microfluidic device (Leng et al., PRL, 96, 2006). Isotropic wormlike micelles have been observed up to 12 % w/w. In a second step, Particle Tracking Microrheology (PTM) was used to investigate the rheological properties of the fluid for surfactant concentrations below 2% w/w in water. Viscosity at low surfactant concentrations (0.1% to 0.3 % w/w), T= 80°C, in synthetic sea water (3.9 % w/w TDS) and in sodium chloride (2 % w/w TDS) has been recorded. Data shows that the viscosity is weakly dependent on brine concentration and evolves between 3 and 15 mPa.s (γ=10 s-1), for surfactant concentrations between respectively 0.1% to 0.3 % w/w. The second series of tests consisted of core-flood experiments at 80°C in Clashach sandstone with brine solution (NaCl 2% w/w) containing surfactant concentrations between 0.1 %w/w and 0.3 %w/w. The surfactant is shown to adsorb moderately on the sandstone (50 μg/g) and displace a great fraction of residual oil (from Sor=0.49 to Sor=0.20). These preliminary results show a strong potential for this new surfactant based viscoelastic fluid in chemical EOR. Compared to other viscoelastic fluids this product shows the following advantages: Superior viscosity, at low surfactant concentration, in hard brine and at high temperature Better displacement of residual oil in core-flood with moderate adsorption

The flow curve of wormlike micelles usually exhibits a stress plateau sigma* separating high and low viscosity branches, leading to shear-banded flows. We study the flow of semidilute wormlike micellar systems in a confined geometry: a straight microchannel. We characterize their local rheology thanks to particle image velocimetry. We show that flow curves cannot be described by a simple constitutive equation linking the local shear stress to the local shear rate. We demonstrate the existence of nonlocal effects in the flow of wormlike micellar systems and make use of a theoretical framework allowing the measurement of correlation lengths.

The flow curve of wormlike micelles usually exhibits a stress plateau σ* separating high and low viscosity branches, leading to shear‐banded flows. We study the flow of semidilute wormlike micellar systems in a confined geometry: a straight microchannel. We characterize their local rheology thanks to particle image velocimetry. We show that flow curves cannot be described by a simple constitutive equation linking the local shear stress to the local shear rate. We demonstrate the existence of nonlocal effects in the flow of wormlike micellar systems and make use of a theoretical framework allowing the measurement of correlation lengths.

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.