Jean-Pierre DELVILLE

1.1 Opto-capillary interface deformation

Thermocapillary stresses are known to deform liquid interfaces. We investigate the case where heating is provided by a continuous Gaussian laser wave and showed that the direction of deformation of the liquid interface strongly depends on the viscosities and the thicknesses of the involved liquid layers. These results provide predictive behaviors for applications where localized thermocapillary stresses are used in confined situations, such as optofluidics.

Flows and interface deformation produced by optocapillary stresses on a water/oil interface heated by a cw laser beam.

Example of steady flow pattern in a double layer configuration

Representative Publications: (1) H. Chraïbi and J. P. Delville, “Thermocapillary flows and interface deformations produced by localized laser heating in confined environment”, Phys. Fluids 24, 032102 (2012).

1.2 Laser-microfluidics

The use of microfluidic drops as microreactors requires active control and manipulation. A route consists in heating locally two immiscible fluids to produce thermocapillary stresses along their interface. This opto-capillary coupling is implemented in adequate microchannel geometries to manipulate two-phase flows and propose a contactless optical toolbox including valves, droplet sorters and switches, droplet dividers or droplet mergers.

Microfluidic valve: Superposition of successive frames illustrating the advance of a droplet front during the formation process, (a) without and (b-c) with opto-capillary blocking.

Microfluidic switch by local thermocapillary actuation (up).

Droplet merger: sequence showing droplet fusion by laser-induced thermocapillary stresses (down)

Microfluidic sampler: In the absence of a laser the mother drop divides into two daughters of same size. Laser forcing allows for breaking this symmetry in a controlled way.

Representative Publications: (1) C. N. Baroud, J. P. Delville, F. Gallaire, R. Wunenburger, “Thermocapillary valve for droplet production and sorting”, Phys. Rev. E 75, 046402 (2007); (2) C. N. Baroud, M. Robert de Saint Vincent, J. P. Delville, “An optical toolbox for total control of droplet microfluidics”, Lab Chip 7, 1029 (2007); (3) M. Robert de Saint Vincent, R. Wunenburger, and J. P. Delville, “Laser switching and sorting for high speed digital microfluidics”, App. Phys. Lett. 92, 154105 (2008); (4) J. P. Delville, M. Robert de Saint Vincent, R. D Schroll, H. Chraibi, B. Issenmann, R. Wunenburger, D. Lasseux, W. W Zhang, E. Brasselet, “Laser microfluidics: fluid actuation by light”, J. Opt. A: Pure Appl. Opt. 11, 034015 (2009); (5) M. Robert de Saint Vincent and J. P. Delville, “Thermocapillary migration in small-scale temperature gradients: application to optofluidic drop dispensing”, Phys. Rev. E 85, 026310 (2012).

2.1 Optical radiation pressure at fluid interfaces

A. Ashkin demonstrated in the seventies that laser waves can deform fluid interfaces by momentum transfer. We have generalized this concept using binary liquid mixtures close to thermodynamic criticality to take advantage of the vanishing behavior of interfacial tension. We investigated this wave/interface interaction experimentally, theoretically and numerically. Moreover, the nonlinear wave/interface coupling leads to a large variety of interface shapes: bell, finger, needle, cone, or pacifier. Some of these shapes can in turn become unstable to give birth to liquid microjets or columns.

Representative Publications: (1) A. Casner, J. P. Delville, “Giant deformations of a liquid-liquid interface induced by the optical radiation pressure”, Phys. Rev. Lett. 87, 054503 (2001); (2) A. Casner, J. P. Delville, “Laser-induced hydrodynamic instability of fluid interfaces”, Phys. Rev. Lett. 90, 144503 (2003); (3) A. Casner et J. P. Delville, “Laser-sustained liquid bridges”, Europhys. Lett. 65, 337 (2004); (4) R. Wunenburger, A. Casner and J. P. Delville, “Light induced deformation and instability of a liquid interface- I. Statics”, Physical Review E 73, 036314 (2006); (5) R. Wunenburger, A. Casner and J. P. Delville, “Light induced deformation and instability of a liquid interface – II. Dynamics”, Physical Review E 73, 036315 (2006); (6) E. Brasselet, J. P. Delville, “Liquid−core liquid−cladding optical fibers sustained by light radiation pressure: Electromagnetic model and geometrical analog”, Phys. Rev. A 78, 013835 (2008); (7) E. Brasselet, R. Wunenburger, J. P Delville, “Liquid optical fibers with multistable core actuated by light radiation pressure”, Phys. Rev. Lett. 101, 014501 (2008); (8) H. Chraïbi, D. Lasseux, E. Arquis, R. Wunenburger, J. P Delville, “Stretching and squeezing of sessile dielectric drops by the optical radiation pressure”, Phys. Rev. E 77, 066706 (2008); (9) H. Chraïbi, D. Lasseux, E. Arquis, R. Wunenburger, J. P Delville, “Simulation of an optically induced asymmetric deformation of a liquid−liquid interface”, Eur. J. of Mech. − B/Fluids 27, 419 (2008); (10) H. Chraïbi, D. Lasseux, R. Wunenburger, E. Arquis, J. P Delville, “Optohydrodynamics of soft fluid interfaces: Optical and viscous nonlinear effects”, Eur. Phys. J. E 32, 43 (2010).

2.2 Optical radiation pressure in bulk liquids

Light momentum transfer can as well occur in bulk for the case of turbid liquids (suspensions, scattering fluids). In this case, the wave induces a liquid flow which can in turn deform fluid interfaces (if present) or keep continuous dripping from a needle tip. All optical microfluidic (channels and flows are here produced by light) becomes at hand.

  

Eddies (left) and tip dripping (right) produced by the scattering of a continuous laser beam propagating in a non-absorbing turbid liquid. 

Broad interface deformation induced by the liquid flow produced by scattering forces; the downward deformation is due to radiation pressure at the interface. Up: experimental; down: numerical simulation

Representative Publications: (1) R. D. Schroll, R. Wunenburger, A. Casner, W. W. Zhang, J. P. Delville, “Liquid Transport due to Light Scattering”, Phys. Rev. Lett. 98, 133601 (2007); (2) R. Wunenburger, B. Issenmann, E. Brasselet, C. Loussert, V. Hourtane, J. P. Delville, “Fluid flows driven by light scattering”, J. Fluid Mechanics 666, 273 (2011); (3) H. Chraibi, R. Wunenburger, D. Lasseux, J. Petit and J. P. Delville, “Eddies and interface deformations induced by optical streaming”; J. Fluid Mech. 688, 195 (2011).

2.3 Acoustic radiation pressure at fluid interfaces

Acoustic radiation pressure can as well deform fluid interfaces. As for the optical case, we investigated this wave/interface interaction experimentally, theoretically and numerically. Moreover, the nonlinear wave/interface coupling still leads to a large variety of interface shapes: bell, finger, needle, cone, or pacifier. Some of these shapes can in turn become unstable to give birth to liquid microjets or columns.

Steady-state deformation of the chloroform-water interface (up) and pacifier-like shape observed at larger acoustic amplitude.

Jet observed at the interface between water and chloroform (left) and acoustically stabilized silicone oil liquid column in water.

Representative Publications: (1) B. Issenmann, A. Nicolas, R. Wunenburger, S. Manneville, J. P. Delville, “Deformation of acoustically transparent fluid interfaces by the acoustic radiation pressure”, Europhysics Letters 83, 34002 (2008); (2) N. Bertin, R. Wunenburger, E. Brasselet, J. P. Delville, “Liquid-Column Sustainment Driven by Acoustic Wave Guiding”, Phys. Rev. Lett. 105, 164501 (2010); (3) B. Issenmann, R. Wunenburger, H. Chraibi, M. Gandil and J. P. Delville, “Unsteady deformations of a free liquid surface caused by radiation pressure”, J. Fluid Mech. 682, 460 (2011).

3.1 Kinetics of liquid-solid phase transition induced by a resonant wave

Laser-induced phase transitions have been extended to the liquid-solid case using one-photon photochemical reactions. The late stage growth of photodeposits can be cast onto a universal behavior, whatever is the type of transition: photoexcitation, photodissociation or photocondensation.

Growth of a Cr (VI) photodeposit on a glass substrate

Universal photodeposit growth law for one-photon photochemical reactions.

Representative Publications: (1) E. Hugonnot, X. Müller, J. P. Delville, “Late-stage kinetics of laser-induced photochemical deposition in liquid solutions”, J. Appl. Phys. 92, 5520 (2002); (2) E. Hugonnot, J. P. Delville, “Kinetic control of surface patterning by laser-induced photochemical deposition in liquid solutions. I. Theoretical developments”, Phys. Rev. E 69, 051605 (2004); (3) E. Hugonnot, A. Popescu, S. Hanifi-Kadi, J. P. Delville, “Kinetic control of surface patterning by laser-induced photochemical deposition in liquid solutions. II. Experimental investigations”, Phys. Rev. E 69, 051606 (2004); (4) E. Hugonnot, M. H. Delville, J. P. Delville, “Universal behavior of photochemical deposition in liquid solutions driven by a one-photon transition”, Phys. Rev. E 75, 061602 (2007).

3.2 Photo-patterning of flat and curved substrates

We applied photochemical deposition to surface patterning; at first on flat substrate with a particular emphasis for the dynamic control of photodeposited holographic gratings; and then to the hemisphere dissymmetrization of spherical particles, to produced Janus beads with a controlled coating, or surface patterned spheres.

Periodic photodeposition performed by computed matrix addressing and dynamic surface relief grating

Radial growth of a circular coating photodeposited on a 10-mm-silica bead

Dissymmetric micropatterning on silica beads

Representative Publications: (1) E. Hugonnot, J. P. Delville, “Kinetics of surface relief gratings tailored by laser-induced photochemical deposition”, Appl. Phys. Lett. 80, 1523 (2002); (2) E. Hugonnot, A. Carles, M. H. Delville, P. Panizza, J. P. Delville, ““Smart” surface dissymmetrization of microparticles driven by laser photochemical deposition”, Langmuir 19, 226 (2003).

3.3 Photodeposit patterning and adhesion

We experimentally and theoretically investigated patterning and adhesion, always assumed and almost never discussed, of coatings photochemically deposited on substrates from photoactive solutions of different compositions and pHs.

Coating patterning and adhesion versus pH variations

Representative Publication: J. P. Delville, E. Hugonnot, C.e Labrugère, T.a Cohen-Bouhacina, and M. H.e Delville, “Patterning and Substrate Adhesion Efficiencies of Solid Films Photodeposited from the Liquid Phase”, J. Phys. Chem. C 114, 19792 (2010).

4.1 Optical nonlinearity in critical liquid mixtures and suspensions

A. Ashkin demonstrated in the eighties that a 100 mw c.w. laser wave is able to induce large optical Kerr effect by manipulating the concentration of artificial liquid suspensions. We have generalized this concept using binary liquid mixtures close to thermodynamic criticality (micellar phases of microemulsions) to take advantage of the divergence of different properties and thus produce “infinite” Kerr response. Local (electrostriction) and nonlocal (thermodiffusion) effects were investigated using self-focusing and wave mixing experiments.

Typical four-wave mixing setup.

Typical dynamical reflectivity in a near critical microemulsion.

Stationnary reflectivity variation when the critical point is neared.

Representative Publications: (1) E. Freysz, A. Ponton, J.P. Delville, A. Ducasse, “Self-focusing induced by Soret effect”, Opt. Comm. 78, 436 (1990); (2) E. Laffon, J.P. Delville, W. Claeys, A. Ducasse, “Non-linéarités optiques de suspensions de vésicules phospholiquides unilamellaires analysées par une expérience de conjugaison de phase”, J. Phys. II (France) 2, 1073 (1992); (3) E. Freysz, E. Laffon, J.P. Delville, A. Ducasse, “Phase conjugation in critical microemulsions”, Phys. Rev. E49, 2141 (1994).

4.2 Laser-induced phase separation by optical manipulation

If the initial concentration is located close to a transition line, the variation of concentration produced by the laser wave (electrostriction and/or thermodiffusion) can be used to quench the mixture in composition and locally induce a phase separation. Drops are nucleated in the beam which behaves as an optical bottle.

Representation of an optical quench in composition on a schematic phase diagram

Liquid-liquid phase transition induced by optical manipulation

Representative Publications: (1) A. Ponton, J.P. Delville, E. Freysz, A. Ducasse, A.M. Bellocq, “Laser-induced structural changes in microemulsions”, Europhys. Lett. 17, 27 (1992); (2) J.P. Delville, C. Lalaude, E. Freysz, A. Ducasse, “Phase separation and droplet nucleation induced by an optical piston”, Phys. Rev. E49, 4145 (1994)

4.3 Optical Hysteresis

The drops nucleated by the optically induced phase separation behave as a set of ball lenses that self-focuses the exciting beam; the corresponding nonlinearity is not of optical origin but has instead a thermodynamic origin. Due to the S-shape of the Van der Waals isotherms, each drop behaves in fact as a bistable ball lens. As the field intercepting a drop depends on its modification by the previous lenses, the medium is equivalent to a set of self-induced bistable ball lenses coupled by the field. Consequently, by analogy with magnetization mechanisms, a hysteretical propagation is expected.

Axial and transverse beam profiles before and after optical quenching

Hysteretical self-focusing induced by the propagation in a set of coupled bistable ball lenses.

Representative Publication: (1) J.P. Delville, E. Freysz, A. Ducasse, “Optical hysteresis in laser-induced liquid-liquid phase separation”, Phys. Rev. E53, 2488 (1996)

4.4 Early Stage Dynamics of liquid-liquid phase transitions in an optical bottle

To access to the nucleation and the early stage growth, the mixture has been quenched in a fring pattern (i) to avoid wetting, (ii) to make use of the tremendous sensitivity of wave mixing experiments and, (iii) to mean polydispersity effects over the droplet distribution.

Dynamics of a growing droplets grating produced in a fringe pattern

Nucleation and early stage growth in reduced variables; comparison with predictions.

Representative Publications: (1) S. Buil, J. P. Delville, E. Freysz, A. Ducasse, “Induced transient gratings as a probe of the early stage kinetics of phase-separating liquid mixtures”, Optics Letters. 23, 1334 (1998); (2) S. Buil, J. P. Delville, A. Ducasse, “Early stage kinetics of phase-separating liquid mixtures”, Physical Review Letters 82, 1895 (1999); (3) S. Buil, J. P. Delville, A. Ducasse, “Nucleation and early stage growth in phase-separating liquid mixtures under weak time-dependent supersaturation”, European Physical Journal E 2, 105 (2000); (4) S. Buil, E. Hugonnot, and J. P. Delville, “Performances of holographic gratings monitored by laser-induced phase separation in liquid mixtures”, Phys. Rev. E 63, 041504 (2001)

4.5 Late Stage Dynamics of liquid-liquid phase transitions in an optical bottle

Beyond observations of classical droplet growth laws, the main originality of these investigations are linked to the confinement inside the optical bottle: (i) contrary to classical experiment no wetting coupling is expected, the beam behaves as a soft-wall bottle; (ii) buoyancy is balanced by radiation pressure, and (iii) the final droplet size is calibrated by the beam and thermodynamic properties. This offered the first opportunity to investigate droplet growth saturation up to thermodynamic equilibrium in the absence of wetting and hydrodynamic couplings.

Late stage growth kinetics in a laser beam.

Late-stage droplet growth law in presence of wetting free finite size effects.

Representative Publications: (1) C. Lalaude, J. P. Delville, S. Buil, A. Ducasse, “Kinetics of crossover in phase-separating liquid mixtures induced by finite size effects” Phys. Rev. Lett. 78, 2156 (1997); (2) J. P. Delville, C. Lalaude, S. Buil, A. Ducasse, “Late stage kinetics of phase separation induced by a cw laser wave in binary liquid mixtures”, Physical. Review E 59, 5804 (1999); (3) J. P. Delville, C. Lalaude, A. Ducasse, “Kinetics of laser-driven phase separation induced by a tightly focused wave in binary liquid mixtures”, Physica A 262, 40 (1999)

5.1 Synthesis of nano and micro silica beads

In closed systems, control over the size of monodisperse metal-oxide colloids is generally limited to submicrometric dimensions. To overcome this difficulty, we explore the formation and growth of silica particles under constant monomer supply. Monodisperse spherical particles are produced up to a mesoscopic size and their growth can be described in an universal way.

Setup used for controlling particle growth under continuous addition

Growth of silica particles at given temperature and flow rate. The bare scale is 200 nm.

Data reduction onto a master behavior of the growth of silica beads investigated at different temperature and flow rates.

Representative Publications: (1) K. Nozawa, M. H. Delville, H. Ushiki, P. Panizza, J. P. Delville, “Growth of monodisperse mesoscopic metal-oxide colloids under constant monomer supply “, Phys. Rev. E 72, 011404 (2005); (2) K. Nozawa, H. Gailhanou, L. Raison, P. Panizza, H. Ushiki, E. Sellier, J. P. Delville, M. H. Delville, “Smart Control of Monodisperse Stöber Silica Particles: Effect of Reactant Addition Rate on Growth Process”, Langmuir 21, 1515 (2005).

5.2 Dynamic interfacial tension

Dynamic interfacial tension effects can be investigated by examining the rupture of fluid necks during droplet formation of surfactant-laden liquids. The temporal behavior of the interfacial tension can be deduced from deviations to expected behaviors for the pinch-off.

Jet breakup in a microchannel under the optocapillary action of a laser beam

Dynamic interfacial tension in presence of laser-induced jet breakup. The thinning dynamics is shown in the inset

Representative Publication: (1) M. Robert de Saint Vincent, J. Petit, M. Aytouna, J. P. Delville, D. Bonn, and H. Kellay, “Dynamic interfacial tension effects in the rupture of liquid necks”, J. Fluid Mech. 692, 499 (2012).

5.3 Devices for digital microfluidic

We developed an optical, microfabrication-free approach for performing real-time measurements of individual droplet characteristics (frequency of production, velocity, and length) flowing in a transparent microfluidic channel.

Signal obtained as a droplet image crosses the photodiodes

Measured frequency, velocity, and length, of droplets produced at imposed flow rates with a KDS 100 Syringe pump.

Representative Publications: (1) M. Robert de Saint Vincent, S. Cassagnère, J. Plantard and J. P. Delville, “Real-time droplet caliper for digital microfluidics”, Microfluid Nanofluid 13, 261 (2012); (2) J. P. Delville, J. Plantard, S. Cassagnères, M. Robert de Saint Vincent, “Measuring device for characterizing two-phase flows”, Patent PCT/FR2010/0004826, published July 03 2009.

5.4 Hydrodynamics in fluctuating systems

We investigated the thinning dynamics of a liquid neck before break-up when the neck reaches dimensions comparable to the thermally excited interfacial fluctuations, as in nanojet break-up or the fragmentation of thermally annealed nanowires. And we fully characterize the universal dynamics of this thermal fluctuation-dominated regime.

Destabilization of a liquid column produced by light after laser interruption and close-up view of the neck thinning before break-up.

Variation of the neck thinning up to breakup. The viscocapillary and the fluctuation-dominated regimes are fit respectively to a linear function and a power law with exponent forced at 0.42. 

Representative Publication: (1) J. Petit, D. Rivière, H. Kellay and J. P. Delville, “Break-up dynamics of fluctuating liquid threads”, Proc. Nat. Ac. Sci. USA 109, 18327 (2012).