arXiv subjects

Jean-Christophe Baret

Publications and source records attributed to Jean-Christophe Baret.

6 recordsLinked to original sources

arXiv2026

Light-driven active phase separation and droplet division

Phase separation organizes matter across scales, yet how it operates under sustained energy input remains poorly understood. Experimental approaches to driven phase separation have largely relied on chemically fueled systems, in which reaction fluxes are intrinsically coupled to fuel consumption and reaction-network complexity. Here we show that continuous molecular switching alone is sufficient to generate active phase behavior in a minimal two-phase system. Using light-responsive DNA-azobenzene coacervates confined in microfluidic droplets, we modulate intermolecular interactions with spatiotemporal precision and quantitatively track phase separation dynamics under illumination. Light-driven azobenzene isomerization controls both thermodynamics and kinetics, setting phase boundaries and regulating dissolution and nucleation rates. Under single-wavelength illumination that couples forward and backward isomerization into a dynamic photostationary state, coarsening is arrested and micron-sized coacervates are stabilized. When the two photoisomerization pathways are driven independently, spatially unbalanced reaction fluxes generate sustained interfacial instabilities, including surface undulations, budding, and division. These behaviors arise from a physical coupling between reaction kinetics and phase separation, without chemical fuels or biochemical regulation. Our results show that non-equilibrium phase behavior is governed by how opposing reaction fluxes are imposed, establishing reversible molecular switching as a minimal route to active materials from equilibrium building blocks.

cond-mat.soft↗

arXiv2024

Emulsion Electrocoalescence in microfluidics: impact of local electric fields

The mechanism of coalescence of aqueous droplet pairs under an electric field is quantitatively studied using microfluidics in quiescent conditions. We experimentally trap droplet pairs and apply electric fields with varying frequencies and formulation compositions. We find that the electrical resistance of the oil used as continuous phase controls the onset of electrocoalescence in quiescent conditions. We observe that the local field enhancement between droplets strongly depends on formulations but also on the number of droplets across the electrodes. These findings provide a better understanding of the onset of electrocoalescence and pave a route towards the rationalization of droplet-based microfluidics operations.

cond-mat.soft↗

arXiv2023

Phase separation dependent active motion of Janus lipid vesicles

Active colloidal systems have emerged as promising contenders for the future of microdevices. While conventional designs have extensively exploited the use of hard colloids, the advancement of cell-inspired architectures represents a pivotal path towards realizing self-regulating and highly functional artificial microswimmers. In this work, we fabricate and actuate Janus lipid vesicles demonstrating reconfigurable motion under an AC electric field. The giant unilamellar vesicles (GUVs) undergo spontaneous phase separation at room temperature leading to Janus-like GUVs with two distinct lipid phases. We report self-propulsion of the Janus GUVs via induced charge electroosmosis, in between parallel electrodes. Remarkably, the fluid nature of the lipid membrane affected by the electric field leads to asymmetry-symmetry transient states resulting in run-and-tumble events supported by structure domain analysis. We characterise an enhanced rotational diffusivity associated with tumble events, decoupled from thermal reorientation. Lastly, we identify cargo-release capabilities and a variety of shape-encoded dynamic modes in these vesicles. This cell-inspired architecture provides an alternative route for creating motile artificial cells and programmable microswimmers.

cond-mat.soft↗

arXiv2019

Rapid Stabilization of Droplets by Particles in Microfluidics: Role of Droplet Formation

Droplet-based microfluidics has emerged as a powerful technology for the miniaturization and automation of biochemical assays. The replacement of surfactants by nanoparticles as interfacial stabilizers has gained increasing interest. However, the stabilization mechanism of droplets by nanoparticles in microchannels is poorly understood, drastically hindering the development of practical applications. Current methods for droplet stabilization involve a trade-off between low droplet production throughput and waste of large number of nanoparticles. Here, we introduce a modification to the droplet production junction that reduces the droplet stabilization time by an order of magnitude, and at the same time significantly reduces the particle waste. Our results show that the limiting step in the kinetics of stabilization is the initial time where both phases come into contact and offer a guideline for the design of particle-stabilized droplet production devices.

cond-mat.soft↗

arXiv2014

Wetting heterogeneity in mixed-wet porous media controls flow dissipation

Pressure controlled displacement of an oil/water interface is studied in dense packings of functionalized glass beads with well-defined spatial wettability correlations. An enhanced dissipation is observed if the typical extension $ξ$ of the same-type wetting domains is smaller than the average bead diameter $d$. Three dimensional imaging using X-ray microtomography shows that the frequency $n(s)$ of residual droplet volumes $s$ for different $ξ$ collapse onto the same curve. This indicates that the additional dissipation for small $ξ$ is due to contact line pinning rather than an increase of capillary break-up/coalescence events.

physics.flu-dyn↗

arXiv2002

An extremal model for amorphous media plasticity

An extremal model for the plasticity of amorphous materials is studied in a simple two-dimensional anti-plane geometry. The steady-state is analyzed through numerical simulations. Long-range spatial and temporal correlations in local slip events are shown to develop, leading to non-trivial and highly anisotropic scaling laws. In particular, the plastic strain is shown to statistically concentrate over a region which tends to align perpendicular to the displacement gradient. By construction, the model can be seen as giving rise to a depinning transition, the threshold of which (i.e. the macroscopic yield stress) also reveal scaling properties reflecting the localization of the activity.

cond-mat.dis-nn↗