Solute Enrichment in Nanochannel: Convective Effects

A long started work by Simon on flow-induced effects in nanochannels. We show a novel effect resembling electric-field-induced concentration polarization. A pressure-driven flow modifies the solute concentration inside nanochannels to generate gradients from homogeneous initial conditions. Combining FCS measurement, theoretical and numerical modeling, Simon quantitatively describe this ubiquitous phenomenon and show how it can be harnessed for ultra-sensitive mass transport measurement in single nanochannel.

See more: Gravelle, Ybert J. Chem. Phys. 151, pp 244503-6 (2019).

 

Self-propulsion of Symmetric Chemical Sources

Chemical cloud around swimming disk (model); Camphor swimmer with controlable asymmetry

Dolachai finalized the work initiated during Ronan’s PhD on the spontaneous swimming of camphor disks lying at the air-water interface, arguably the oldest active system ever! Besides experimental characterization, we propose a very simple model to deals with the generics of swimming by symmetry-breaking.
See more: Boniface et al., Phys. rev. E 99, pp 062605-13 (2019).

Swim polarization in sedimenting active colloids

PDF of the active colloids velocity. The sedimenting angle increases from (a) to (d) showing the onset of swimming polarization upward.

Félix eventually managed to complete ideas he shared with Julien and Alexandre some times ago. Carefully controlling the sedimentation of our active colloids and gathering statistics on their instantaneous velocities, he was able to experimentally demonstrate the orientational swim polarization predicted some years ago. A good opportunity to confront experimental figures with theoretical predictions on sedimenting profiles and pressure(s) build up.
See more: Ginot et al., New J. Phys. 20, pp 115001 (2018).

Rationalizing the coupling between advective and diffusiophoretic transport

Maximum Phoretic Focusing for different flows characteristics.

Following our experimental, and numerical previous works, we continue to explore the effect of phoretic effects on the transport and mixing of suspended particles. Still in collaboration with our colleaguesat ENS de Lyon and LMFA we explore here the coupling between linear flows (shear flow and convergent-divergent flow) and diffusio- or thermophoretic drift of articles. This fully tractable analytical problem allows pointing remarkable properties of phoretic particle transport and to identify the proper framework of description. This puts forward the compressible nature of the particle velocity field in close analogy with the problem involved with inertial particles’ transport.
See more: Raynal et al., J. Fluid Mech. 247, pp 228-243 (2018)

Electroosmosis of soap Interfaces

Baptiste’s work on the electroosmotic response of soap interfaces. In collaboration with the Nonlinear optics group @iLM, we simultaneously investigated the flow field generated underneath surfactant-laden air/water interfaces, and the spatially-resolved surface concentration of surfactant molecules. This original combination of techniques reveals the generation of electroosmotic flows while keeping an homogeneous surfactant distribution, suggesting that no surface motility is involved. This paves the way for the better understanding of the electrokinetics at fluid interfaces.

See more: Blanc et al. Soft Matter 14, pp 2604-2609 (2018).