Slides - Fondation Nanosciences

Rheology of micro-swimmersuspensionsSalima Rafaï, Levan Jibuti and Philippe PeylaLSP- University Joseph Fourier – CNRS – GrenobleCIBLE Programme – Rhône-Alpes Region

Rheology (viscosimetry) ofactive suspensionsChlamydomonasSpermatozoaE. Coliparamecia

Rheology (viscosimetry) ofactive suspensionsMacroscopicProperty effChlamydomonasSpermatozoaE. ColiMicroscopicPropertyMotility(velocity)paramecia

Rheology of chlamydomonassuspensions10mUnicellular micro-alga2 Anterior flagella (puller)50 Hz breast-strokeA swimming chlamyRapid camera 500Hz

Chlamydomonas = swimmer without inertiaLow reynolds number motionRe=VR/ V=40m/sR=10 m=10 -6 m 2 /sNo inertiaHight reynolds number motionRe=VR/ V=10 m/sR=10 m=10 -6 m 2 /sInertia

Chlamydomonas = swimmer without inertiaAt low Reynolds number,a time-reversible motion is inefficient for swimmingScallop theorem (Purcell, 1975)InertiaRe>>1No InertiaRe

Effective viscosityof chlamydomonas suspensions=5s -1 eff Volume fraction=V chlamys/ V suspension

A 3D model of chlamydomonas-FBeating of flagella 50Hz10m-F/2-F/2Unicellular micro-alga2 Anterior flagella (puller)50 Hz breast-stroke3D Model:Chlamy = sphere+multipole of forcesP. Nott, JFM 2008 (2D model)

Model for the rheology of active suspensionsMMMM3D Fluid particle dynamics- Tanaka et al, PRL, 2000- Peyla et al, EPL 2007, EPL 2008

Rheology of active suspensionswith non-rotary particles eff MMMMIshikawa & Pedley, JFM, 2007

Rheology of active suspensionsZYA dead chlamyis simply tumblingin the shear flowA live chlamymaintains its directionin the shear flowZZXDeadLiveX y =/2YX y =Y

Rheology of active suspensionswith non-rotary particles=1 eff =0.0G is a fixe torque that slow down the rotationMGMMM=G/(8R 3 Howard Brenner, 1965(dilute polar suspensions)

Rheology of active suspensionsZYA dead chlamyis simply tumblingin the shear flowA live chlamymaintains its directionin the shear flowZZXDeadLiveX y =/2YX y =Y

Rheology of active suspensionswith non-rotary particles=1 eff =0.0G is a fixe torque that slow down the rotationMGMMM=G/(8R 3 Howard Brenner, 1965(dilute polar suspensions)

Rheology of active suspensionswith non-rotary particlesGMMMM(η eff−η 0)/η 0Shear thiningΘ=1Θ=0.5Θ=0.33Θ=0.0Θ=G/(8πR 3 γ/2)

Outcomes• Fixe orientation of the live chlamy → rheological signature (higher η eff)• Origin of this phenomenon still an open question….- drag force of the flagella- Effect of gravity-…Experiment with a single chlamy dynamics in a shear→ more complex modelization•This method can help to diagnose the motility of a big population of motile cellsToward a test of motility for spermatozoa- simple and quantitative- million of cells are tested.

« And now let’s go for somethingcompletely different… »• Natural micro-swimmers• Artificial nano-swimmers

Au/Pt nanoswimmers2 H 2 O 2(aq) 2 H 2 O+O 2(aq)400 nmAuPt2μmChem. Eur. J. 11, 6462 (2005)Paxton, Sen, MalloukPlatinum nanorods composite (Janus particles)

Au/Pt NanoswimmersChem. Eur. J. 11, 6462 (2005)Paxton, Sen, Mallouk2 H 2 O 2(aq)2 H 2 O+O 2(aq)AuPtH 2O 2(%) Speed (μms -1 ) Directionality (s) Axial velocity (μms -1 )4.9 7.7 ± 0.9 0.078 6.6 ± 1.03.3 7.9 ± 0.7 0.075 6.6 ± 0.71.6 5.6 ± 0.6 0.065 4.0 ± 0.80.33 4.9 ± 0.3 0.060 3.4 ± 0.40.031 3.9 ± 0.5 0.019 0.9 ± 0.4Pure water 3.7 ± 0.3 0.007 0.4 ± 0.1

Au/Pt NanoswimmersL2RAuPtVF drag =ζV=2πμL/[ln(2L/R)-0.72) Vμ=10 -3 Pa.s L=2μm R=185nmF drag=0.048 pNNo inertia :Drag forceChemical forceF drag +F κ +η=0Random force

Concentrationdifference ΔO 2Au/Pt NanoswimmersAuPtO 2 bubblesVxSurface tension (γ) is different : Δγ (Marangoni effect)dF κ =dγ/dx 2πR dxF κ = ∫ L dF=∫ L dγ/dx 2πR dx=Δγ 2πRFor F=0.048 pN, we need Δγ=0.041 pNμm−1This correspond to a ΔO 2=3.1 10 -5 MBased on an experimental estimation ΔO 2=6.6 10 -5 M

Au/Pt Nanoswimmers suspensionsA new artificial active fluidWith collective effects:•Self-organization•Chimiotaxis (Motion ingradients)•Rheology•Micro-fluidicsBUT high concentrations are needed:20-30%, 10 nl per sample ~ 10 6 particles!!

Erasmus – Mundus MasterNanoscience and NanotechnologyNanophysicsNanochemistryNano-biotechnologyNano-engineering1st Year : Leuven (Belgium) -¨Partnership with IMEC2sd Year : Dresden (Germany), Chalmers (Göteborg, Sweden),Grenoble (France) partnership with LETI