Light-controlled flows in active fluids

Dervaux, Julien; Resta, Marina Capellazzi; Brunet, Philippe

doi:10.1038/nphys3926

Cited by 34 publications

(55 citation statements)

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“…Water has a surface tension γ = 72 mN m −1 , a density ρ = 1000 kg m −3 , and a dynamic viscosity η = 10 −3 Pa s. In Fig. 6 we plot the threshold velocities at which biological contaminants are expected to be entrained in the liquid film on the flat plate based on physical values found in the literature [40][41][42][43][44][45][46][47]. For microorganisms such as bacteria and parasites, the substrate needs to be pulled out of the polluted water at velocities smaller than 10 −2 − 10 −1 mm s −1 to prevent contamination.…”

Section: Application To Biological Contaminationmentioning

confidence: 99%

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Capillary filtering of particles during dip coating

et al. 2019

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An object withdrawn from a liquid bath is coated with a thin layer of liquid. Along with the liquid, impurities such as particles present in the bath can be transferred to the withdrawn substrate. Entrained particles locally modify the thickness of the film, hence altering the quality and properties of the coating. In this study, we show that it is possible to entrain the liquid alone and avoid contamination of the substrate, at sufficiently low withdrawal velocity in diluted suspensions. Using a model system consisting of a plate exiting a liquid bath, we observe that particles can remain trapped in the meniscus which exerts a resistive capillary force to the entrainment. We characterize different entrainment regimes as the withdrawal velocity increases: from a pure liquid film, to a liquid film containing clusters of particles, and eventually individual particles. This capillary filtration is an effective barrier against the contamination of substrates withdrawn from a polluted bath and finds application against biocontamination.

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Section: Application To Biological Contaminationmentioning

confidence: 99%

“…(3). The arrow indicates the range of size of different biological organisms[40][41][42][43][44][45]. The solid symbols and the open symbols indicates contaminated and noncontaminated substrates, respectively.…”

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confidence: 99%

Capillary filtering of particles during dip coating

et al. 2019

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“…Microscopic flow fields [3][4][5] can lead to large-scale collective motion [6][7][8] with enhanced drug resistance [9,10], surprising rheological properties [11][12][13], and global features controllable by structured confinement [14][15][16][17][18]. When coupled with population-wide taxis, these flows result in macroscopic instabilities [19][20][21] which increase nutrient fluxes [22] and can provide unexpected new avenues for capture and manipulation of small objects [23].…”

Section: Introductionmentioning

confidence: 99%

Universal entrainment mechanism controls contact times with motile cells

2018

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Contact between particles and motile cells underpins a wide variety of biological processes, from nutrient capture and ligand binding, to grazing, viral infection and cell-cell communication. The window of opportunity for these interactions depends on the basic mechanism determining contact time, which is currently unknown. By combining experiments on three different species -Chlamydomonas reinhardtii, Tetraselmis subcordiforms, and Oxyrrhis marina-simulations and analytical modelling, we show that the fundamental physical process regulating proximity to a swimming microorganism is hydrodynamic particle entrainment. The resulting distribution of contact times is derived within the framework of Taylor dispersion as a competition between advection by the cell surface and microparticle diffusion, and predicts the existence of an optimal tracer size that is also observed experimentally. Spatial organisation of flagella, swimming speed, swimmer and tracer size influence entrainment features and provide trade-offs that may be tuned to optimise the estimated probabilities for microbial interactions like predation and infection. * A.M. and R.J. contributed equally to this work and are joint lead authors. A.M., R.J. and M.P. designed the study, analysed results, developed the theory, wrote the manuscript; R.J. performed the experiments; A.M. developed the model, performed simulations. † R.J. Current Address: IMEDEA, University of the Balearic Islands, Carrer de Miquel Marquès, 21 07190 Esporles, Illes Balears ‡ Correspondence: M.Polin@warwick.ac.uk (S) J above the length L (S) M at the peak of the distribution. Exponential fits to these curves give L (CR) J = 9.2 ± 0.6 µm for CR, L (TS) J = 7.4 ± 1.2 µm for TS and L (OM) J = 11.7 ± 1.4 µm for OM, while we find L (CR) M ≈ 6.7 µm, L (TS) M ≈ 8.6 µm and L (OM) M ≈ 7.5 µm. Unexpectedly, the characteristic entrainment length L (S) J

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“…It is highly flexible as the the spatiotemporal modulation of illumination tunes the velocity of particles, and subsequent density 40,41 , with a micron-resolution and can conveniently be switched on and off 42 . The superimposition of light gradients can direct the motion of particles, as for biological cells 43 , self-electrophoretic nanotrees 44,45 , or photocatalytic symmetric 37,46,47 or Janus 38,48 microswimmers. In this paper, we show how light patterns can be used with photocatalytic particles to control the phenomenon of diffusiophoresis, the motion of a colloidal particle along a gradient of chemicals 49,50,[50][51][52][53] .…”

Section: Introductionmentioning

confidence: 99%

Diffusiophoretic design of self-spinning microgears from colloidal microswimmers

Aubret

Palacci

2018

Soft Matter

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Design strategies to assemble dissipative building blocks are essential to create novel and smart materials and machines. We recently demonstrated the hierarchical self-assembly of phoretic microswimmers into self-spinning microgears and their synchronization by diffusiophoretic interactions [Aubret et al., Nature Physics, 2018]. In this paper, we adopt a pedagogical approach and expose our strategy to control self-assembly and build machines using phoretic phenomena. We notably introduce Highly Inclined Laminated Optical sheets microscopy (HILO) to image and quantify anisotropic and dynamic diffusiophoretic interactions, which could not be observed by standard fluorescence microscopy. The dynamics of a (haematite) photocalytic material immersed in (hydrogen peroxide) fuel under various illumination patterns is first described and quantitatively rationalized by a model of diffusiophoresis, the migration of a colloidal particle in a concentration gradient. It is further exploited to design phototactic microswimmers, that direct towards the high intensity of light, as a result of the the torque exerted by the haematite in a light gradient on a microswimmer. We finally demonstrate the assembly of self-spinning microgears from colloidal microswimmers by controlling dissipative diffusiophoretic interactions, that we characterize using HILO and quantitatively compare to analytical and numerical predictions. Because the approach described hereby is generic, this works paves the way for the rational design of machines by controlling phoretic phenomena.

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Light-controlled flows in active fluids

Cited by 34 publications

References 50 publications

Capillary filtering of particles during dip coating

Capillary filtering of particles during dip coating

Universal entrainment mechanism controls contact times with motile cells

Diffusiophoretic design of self-spinning microgears from colloidal microswimmers

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