arXiv subjects

Antoine Deblais

Publications and source records attributed to Antoine Deblais.

13 recordsLinked to original sources

arXiv2026

Active Reinforcement of Jammed Emulsions by Living Microswimmers

We show that living microswimmers mechanically reinforce dense emulsions. Castor-oil-in-water emulsions laden with the microalga Chlamydomonas reinhardtii are compared in three states: without algae, with immobilized algae, and with motile algae, over a broad range of oil fractions spanning the jamming transition. Oscillatory rheology reveals that motile algae systematically increase the yield stress, by up to a factor of two, whereas immobilized cells at the same concentration leave it essentially unchanged. The reinforcement thus originates from activity rather than from the mere presence of inclusions. Single-cell tracking shows that the droplet network confines the swimmers in pores that shrink as the oil fraction increases, and confinement is known to amplify the propulsion force of C. reinhardtii. A simple estimate based on this confinement-enhanced force accounts for the measured excess yield stress and indicates an effective, activity-induced depletion-like attraction between the passive droplets. These results identify a feedback loop: the microstructure confines the swimmers, confinement amplifies the forces they exert, and these forces stiffen the microstructure. Active emulsions thus emerge as a model platform for programming the mechanics of disordered soft solids through activity.

cond-mat.soft↗

arXiv2025

Emergent Isotropic-Nematic Transition in 3D Semiflexible Active Polymers

Active semiflexible filament collectives, ranging from motor-driven cytoskeletal filaments to slender organisms such as cyanobacteria and worm aggregates, abound in nature. Yet how activity and flexibility jointly govern their organization, especially Isotropic-Nematic (I-N) transition, remains poorly understood. Performing large-scale Brownian dynamics simulations of 3D active semiflexible polymers with varying flexibility degrees, we show that tangential active forces systematically shift the I-N transition to higher densities, with the shift controlled by the flexibility degree and activity strength. Strikingly, activity alters the nature of the transition: discontinuous at low strengths, continuous at moderate strengths, and ultimately suppressed at high activity levels. The delayed I-N transition originates from enhanced collective bending fluctuations, resulting in chain shrinkage and enlargement of effective confinement tube. At moderate activity levels, these fluctuations can trigger large-scale excitations that stochastically drive temporal transitions between nematic and isotropic states, indicating an activity-induced instability of the nematic field. We summarize this behavior in non-equilibrium state diagrams of density and activity for different flexibility degrees.

cond-mat.soft↗

arXiv2025

Optimal Translocation of Living \& Active Filaments in Confinement

Active filament translocation through confined spaces is central to processes ranging from DNA transport through nanopores to cytoskeletal dynamics in cell migration. Here, we use living filamentous \textit{Tubifex tubifex} worms as a model system to investigate how activity and filament conformation govern transport in confinement. By tuning activity via temperature and tracking worm dynamics in a two-chamber geometry connected by a narrow bridge, we quantify their translocation behavior and conformational states. In contrast to passive polymers and filaments, we find that contour length has negligible influence on trapping dynamics, while activity and reorientation jointly control escape. Strikingly, translocation efficiency is maximized at an intermediate temperature ($20^\circ$C), where a balance between directed propulsion and rotational diffusion optimizes exploration. We show that trapping times are governed by the interplay between the timescale of conformational rearrangements and the conformational entropy, quantifying the diversity of accessible shapes. Simulations of tangentially driven active filaments quantitatively reproduce the experimental observations and provide a minimal physical framework to rationalize the existence of an optimal activity. More broadly, our results identify general principles governing active filament transport in confinement, with implications for both biological systems and the design of synthetic active slender objects.

cond-mat.soft↗

arXiv2024

Drop-drop coalescence: a simple crossover function between inertial and viscous dynamics

The coalescence of liquid drops is a fundamental process that remains incompletely understood, particularly in the intermediate regimes where capillary, viscous, and inertial forces are comparable. Here, we experimentally investigate the dynamics of drop-to-drop coalescence during the transition between viscous and inertial regimes using high-speed imaging. Our results reveal that the liquid bridge between droplets shows power-law growth with exponents between 1/2 and 1 during drop coalescence. We propose a novel scaling approach using a dimensionless crossover function that smoothly transitions between viscous and inertial limits. This simple approach, inspired by previous work on drop impact, successfully collapses the experimental data for a wide range of liquid viscosities and coalescence times onto a single master curve. We further compare our results with recent theoretical models and demonstrate how our approach complements and extends current understanding in the crossover of drop coalescence. This study contributes to both the fundamental physics of drop coalescence and its practical applications in various industrial processes.

physics.flu-dyn↗

arXiv2024

Locomotion of Active Polymerlike Worms in Porous Media

We investigate the locomotion of thin, living T. tubifex worms, which display active polymerlike behavior, within quasi-2D arrays of cylindrical pillars, examining varying spatial arrangements and densities. These active worms spread in crowded environments, with a dynamics dependent on both the concentration and arrangement of obstacles. In contrast to passive polymers, our results reveal that in disordered configurations, increasing the pillar density enhances the long-time diffusion of our active polymer-like worms, while we observe the opposite trend in ordered pillar arrays. We found that in disordered media, living worms reptate through available curvilinear tubes, whereas they become trapped within pores of ordered media. Intriguingly, we show that reducing the worm's activity significantly boosts its spread, enabling passive sorting of worms by activity level. Our experimental observations are corroborated through simulations of the tangentially driven polymer model with matched persistence length predicting the same trends.

cond-mat.soft↗

arXiv2024

Early Stages of Drop Coalescence

Despite the large body of research on coalescence, firm agreement between experiment, theory, and computation has not been established for the very first moments following the initial contact of two liquid volumes. Combining a range of experimental and computational modeling approaches in two different geometries, namely drop-drop and drop-bath configurations, we have been able to elucidate the influence of the intervening gas and van der Waals forces on coalescence. For simple liquids considered here, the gas influences both pre- and post-contact regimes, with jump-to-contact being the primary mode of merging. Subsequently, wave-like air pockets are observed and ultimately influence the initial opening dynamics of the neck.

physics.flu-dyn↗

arXiv2023

Beware of CaBER: Filament thinning rheometry does not always give `the' relaxation time of polymer solutions

The viscoelastic relaxation time of a polymer solution is often measured using Capillary Breakup Extensional Rheometry (CaBER) where a droplet is placed between two plates which are pulled apart to form a thinning filament. For a slow plate retraction protocol, required to avoid inertio-capillary oscillations for low-viscosity liquids, we show experimentally that the CaBER relaxation time $\tau_e$ inferred from the exponential thinning regime is in fact an apparent relaxation time that may increase significantly when increasing the plate diameter and the droplet volume. Similarly, we observe that $\tau_e$ increases with the plate diameter for the classical step-strain plate separation protocol of a commercial (Haake) CaBER device and increases with the nozzle diameter for a Dripping-onto-Substrate (DoS) method. This dependence on the flow history before the formation of the viscoelastic filament is in contradiction with polymer models such as Oldroyd-B that predict a filament thinning rate $1/3\tau$ ($\tau$ being the model's relaxation time) which is a material property independent of geometrical factors. We show that this is not due to artefacts such as solvent evaporation or polymer degradation and that it can only be rationalised by finite extensibility effects (FENE-P model) for a dilute polymer solution in a viscous solvent, but not for semi-dilute solutions in a low-viscosity solvent.

cond-mat.soft↗

arXiv2023

Worm Blobs as Entangled Living Polymers: From Topological Active Matter to Flexible Soft Robot Collectives

Recently, long and slender living worms have garnered significant interest because of their impressive ability to exhibit diverse emergent behaviors in highly entangled physical and topological conditions. These worms can form an active viscoelastic, three-dimensional soft entity known as the 'blob', which can behave like a solid, flow like a liquid, and even respond to external stimuli such as light to locomote or change shape. To understand the behavior of the blob, it is crucial to consider the high degree of conformational entanglement that individual units can achieve because of their high aspect ratio and tunable activity. This topologically active collective necessitates reevaluating established soft matter concepts in polymer physics to advance the development of active polymer-like materials. Our understanding of the complex emergent dynamics of the worm blob promises to catalyze further research into the behavior of entangled active polymers and guide the design of synthetic topological active matter and bioinspired tangling soft robot collectives.

cond-mat.soft↗

arXiv2023

Surface-Mediated Molecular Transport of a Lipophilic Fluorescent Probe in Polydisperse Oil-in-Water Emulsions

Emulsions often act as carriers for water-insoluble solutes that are delivered to a specific target. The molecular transport of solutes in emulsions can be facilitated by surfactants and is often limited by diffusion through the continuous phase. We here investigate this transport on a molecular scale by using a lipophilic molecular rotor as a proxy for solutes. Using fluorescence lifetime microscopy we track the transport of these molecules from the continuous phase towards the dispersed phase in polydisperse oil-in-water emulsions. We show that this transport comprises two timescales, which vary significantly with droplet size and surfactant concentration, and, depending on the type of surfactant used, can be limited either by transport across the oil-water interface, or by diffusion through the continuous phase. By studying the time-resolved fluorescence of the fluorophore, accompanied by molecular dynamics simulations, we demonstrate how the rate of transport observed on a macroscopic scale can be explained in terms of the local environment that the probe molecules are exposed to.

cond-mat.soft↗

arXiv2021

Emulsion Destabilization by Squeeze Flow

There is a large debate on the destabilization mechanism of emulsions. We present a simple technique using mechanical compression to destabilize oil-in-water emulsions. Upon compression of the emulsion, the continuous aqueous phase is squeezed out, while the dispersed oil phase progressively deforms from circular to honeycomb-like shapes. The films that separate the oil droplets are observed to thin and break at a critical oil/water ratio, leading to coalescence events. Electrostatic interactions and local droplet rearrangements do not determine film rupture. Instead, the destabilization occurs like an avalanche propagating through the system, starting at areas where the film thickness is smallest.

cond-mat.soft↗

arXiv2021

Creep and drainage in the fast destabilization of emulsions Creep and drainage in the fast destabilization of emulsions

The destabilization of emulsions is important for many applications but remains incompletely understood. We perform squeeze flow measurements on oil-in-water emulsions, finding that the spontaneous destabilization of emulsions is generally very slow under normal conditions, with a characteristic time scale given by the drainage of the continuous phase and the coalescence of the dispersed phase. We show that if the emulsion is compressed between two plates, the destabilization can be sped up significantly; on the one hand, the drainage is faster due to the application of the squeezing force. On the other hand, creep processes lead to rearrangements that also contribute to the destabilization.

cond-mat.soft↗

arXiv2021

Light-switchable deposits from evaporating drops containing motile microalgae

Deposits from evaporating drops have shown to take a variety of shapes, depending on the physicochemical properties of both solute and solvent. Classically, the evaporation of drops of colloidal suspensions leads to the so-called coffee ring effect, caused by radially outward flows. Here we investigate deposits from evaporating drops containing living motile microalgae (Chlamydomonas reinhardtii), which are capable of resisting these flows. We show that utilizing their light-sensitivity allows to control the final pattern: adjusting the wavelength and incident angle of the light source enables to force the formation, completely suppress and even direct the spatial structure of algal coffee rings.

cond-mat.soft↗

arXiv2019

Rheology of Active Polymer-like T. Tubifex Worms

Of all complex fluids, it is probably the rheology of polymers we understand best. In-depth insight into the entanglement and reptation of individual polymers allows us to predict for instance the shear-thinning rheology and the behaviour in virtually any flow situation of practical importance. The situation is markedly different when we move from passive to active polymers where the coupling of filament activity, hydrodynamic interactions, and conformations open the way to a plethora of novel structural and dynamical features. Here we experimentally study the rheology of long, slender and entangled living worms (Tubifex tubifex) and propose this system as a new type of active polymer. Its level of activity can be controlled by changing the temperature or by adding small amounts of alcohol to make the worms temporarily inactive. We find that (i) shear thinning is reduced by activity, (ii) the characteristic shear rate for the onset of shear-thinning is given by the time scale of the activity, and (iii) the low shear viscosity as a function of concentration shows a very different scaling from that of regular polymers. Our study paves the way towards a new research field of `living polymers'.

cond-mat.soft↗