Jacques Leng

Microevaporators 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 modeling, 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.

Dynamics of lamellar phase under flow.

We present a short review of what we name the “onion” phase. This phase results from shearing a lyotropic phase. It is obtained when a lamellar phase (smectic A phase) made of surfactant and water is submitted to a constant shear rate above a critical value. The lamellar to onion transition is described as an instability and corresponds to an out-of-equilibrium transition. This phase can be described as a phase of multi-lamellar vesicles (of micrometric size) filling up space. We presents experimental observations of the nature of the structural organization of these vesicles under flow. Consequences on the visco-elasticity of the lamellar phase are described and the evolution of the theoretical understanding is discussed.

Resonant ultrasonic attenuation in emulsions

We report the achievement of scattering resonant emulsions devoted to the frequency-control of acoustic attenuation in the megahertz range. By means of robotics, we produced highly monodisperse, in both size and shape, fluorinated-oil droplet suspensions, providing experimental evidence of several Mie scattering resonances. Ultrasonic experiments performed in such complex media are compared, with an excellent quantitative agreement, to theoretical predictions derived within the framework of the independent scattering approximation.