Interfacial materials, such as foams, emulsions, are composed of many bubbles and drops, stabilized either by surfactants, polymers or colloids. The question we tackle is : « how do molecular interactions and interfacial dynamics in the surfactant layers control the macroscopic properties of foams, emulsions or capsules? ». We have a special interest in « reactive » systems, whose dynamics is out of equilibrium due to a chemical reaction or a phase transition or an environmental stimulation. In such conditions the interfacial dynamics such as adsorption/desorption fluxes can be strongly modified. From a fundamental point of view, we study how a tiny modification at the molecular scale of the viscosity, interfacial tension, adsorption fluxes has consequences at the mesoscopic and macroscopic scales.

AQUEOUS FOAMS AS CHEMICAL REACTORS : OXIDATION OF METALS AND APPLICATION TO THE RECYCLING OF METALS

Foams, are composed of many bubbles, stabilized by adsorbed surfactant molecules. They contain 90% of gas and 10% of liquid. We are currently using foams to oxidize and dissolve metals in the context of the recycling of metals in electronic wastes. We showed that oxygen, O2, present in the bubbles can oxidize metals in the presence of H+ ions in the continuous phase. We showed that the transfer of O2 and H+ controls the kinetics of the oxidation of Cu into Cu2+.

Publications

  • Relation between oxidation kinetics and reactant transport in an aqueous foam, P. Trinh, A. Mikhailovskaya, G. Lefèvre, N. Pantoustier, P. Perrin, E. Lorenceau, B. Dollet and C. Monteux J. Colloid and Interface Sciences, 2023, 10.1016/j.jcis.2023.03.140
  • Leaching foams : toward a more environmentally friendly process to recover metals from electronic wastes, P. Trinh, ACS Sustainable Chemistry and Engineering, 2021, doi.org/10.1021/acssuschemeng.1c02258

ASSEMBLING POLYMERS AT LIQUID INTERFACES

Interfacial rheology of H-bonded layer by layer assembly of polymers for encapsulation

We have assembled polymers layer by layer at liquid interfaces and showed that controlling the interaction between the polymers enables to control the interfacial rheology of the mulitlayers.

We have developped a microfluidic chip that enables to probe the interfacial tension and interfacial moduli of capsules obtained by assembling polymer molecules layer-by-layer at the oil/water interface. The capsules go through a constriction followed by an elongation chamber in which an extensional flow is obtained. By varying the interactions between the polymer layers in the membrane as well as the anchoring energy of the first layer to the interface, we are able to tune the resistance of the membrane to shear and elongation or compression, which controls their behaviour in the constriction/elongation chambers.

Collaborations: M. Reyssat (ESPCI), T. Salez (LOMA), P. Perrin (ESPCI), N. Pantoustier (ESPCI), G. Fuller (Stanford), J. Vermant (ETH)

Publications

  • « Microfluidic probing of complex interfacial rheology capsules », Tregouet, C., Salez, T., Monteux* C., Reyssat*, M., Soft Matter, 15 (13), 2782-2790, (2019) 10.1039/c8sm02507j
  • Transient deformation of a droplet near a microfluidic constriction: A quantitative analysis, Trégouët, C., Salez, T., Monteux*, C. & Reyssat*, M. Phys. Rev. Fluids3, 053603 (2018). 10.1103/PhysRevFluids.3.053603
  • Probing the adsorption/desorption of amphiphilic polymers at the air-water interface during large interfacial deformations Tregouet, C., Salez, T., Pantoustier, N., Perrin, P., Reyssat*, M., Monteux*, C., Soft Matter, (2019) 10.1039/c9sm00368a
  • Trégouët, C. et al. Adsorption dynamics of hydrophobically modified polymers at an air-water interface. Eur. Phys. J. E 41, (2018).
  • Dupré de Baubigny, J. et al. One-Step Fabrication of pH-Responsive Membranes and Microcapsules through Interfacial H-Bond Polymer Complexation. Sci. Rep. 7, (2017).
  • Le Tirilly, S. et al. Interfacial Rheology of Hydrogen-Bonded Polymer Multilayers Assembled at Liquid Interfaces: Influence of Anchoring Energy and Hydrophobic Interactions. Langmuir 32, 6089–6096 (2016).
  • Le Tirilly, S. et al. Interplay of Hydrogen Bonding and Hydrophobic Interactions to Control the Mechanical Properties of Polymer Multilayers at the Oil–Water Interface. ACS Macro Lett. 4, 25–29 (2015).
Impacting and gelling droplets

Encapsulation is a process that enables to protect, transport and deliver active species in dedicated areas. One encapsulation process is the alginate/calcium dripping method, where droplets of a biopolymer, alginate are dripped on a calcium bath where the calcium ions diffuse into the polymer droplets and bind the molecules together to obtain a hydrogel bead. We investigate the shape relaxation of these gelling droplets. We show experimentally and numerically that a gelled layer grows at the surface. Due to volume contraction of the gelling shell, this layer induces tensile stresses and drives the flow of the ungelled liquid core, resulting in the relaxation of the droplets toward spherical shapes. Over time the thickness of this elastic membrane grows hence the bending stiffness required to change its shape eventually balances the surface stresses, which arrests the relaxation process.
These results provide general rules to understand the shape of solidifying materials combining both tension and bending driven deformations.

Surface stress and shape relaxation of gelling droplets, J. Godefroid, A. Marcellan, D. Bouttes, E. Barthel, C. Monteux, Soft Matter, 2023 10.1039/D3SM00533J,  hal-04217557v1

Highly stable foams made from assembled complex fluids

Increasing the stability of foams is a crucial issue in many applications such as surface decontamination or food products.We explore several possibilities to produce highly stable foams by increasing the viscosity of the bulk phase. For example highly stable foams can be obtained by stabilizing the foam with amphiphilic polymer chains which can be assembled into a non covalent network using hydrogen interactions. Cross-linking the polymer chains both at the interface and in bulk results in high interfacial and bulk viscosities which lead to highly stable foams.

  • Deleurence, R., Saison, T., Lequeux, F. & Monteux, C. Time scales for drainage and imbibition in gellified foams: application to decontamination processes. Soft Matter, 11, 7032–7037 (2015).
  • Deleurence, R., Saison, T., Lequeux, F. & Monteux, C. Foaming of Transient Polymer Hydrogels. ACS Omega 3, 1864–1870 (2018).
  • Mixtures of latex and surfactants of opposite charge as interface stabilizers, R. Deleurence, C. Parneix, C. Monteux*, Soft Matter, 10, 7088-7095 (2014)
  • Foamability and foam stability of silica/PEI gels, R. Deleurence, T. Saison, F. Lequeux, C. Monteux*, Colloids and Surfaces A, 534, 2-7 (2017)

FREEZING BUBBLES AND DROPS

The solidification of liquids containing bubbles and drops is of great interest in materials sciences. The fabrication of solid foams often starts with a precursor liquid foam which is then solidified. The fabrication of single crystals requires the exclusion of air bubbles during the crystallization process. We study a model system : the growth of ice crystals growing in a liquid containing bubbles or drops. During the growth of the ice, the surfactants, which are not soluble in the ice, accumulate at the ice/water interface. This concentration gradient induces forces that control the interaction between the drop and the ice crystals.

Collaboration : S. Deville (ILM Lyon)

Publications :

  • Solute effects on dynamics and deformation of droplets during freezing, Tyaggi, S., Monteux, C., Deville, S., Soft Matter, 2022, 10.1039/D2SM00226D
  • Multiple objects encountering a solidifying front , S. Tyagi, C. Monteux, S. Deville, Sci. Rep, 11, 1-14 (2021)
  • Objects interacting with solidification fronts : thermal and solute effects, Materialia, 12, 100802 (2020), 10.1016/j.mtla.2020.100802
  • A temperature-controlled stage for laser scanning confocal microscopy and case studies in materials science, Dedovets, D., Monteux, C. & Deville, S. Ultramicroscopy 195, 1–11 (2018). 10.1016/j.ultramic.2018.08.009
  • Five-dimensional imaging of freezing emulsions with solute effects, Dedovets, D., Monteux, C. & Deville*, S. Science 360, 303–306 (2018). 10.1126/science.aar4503

DYNAMICS OF COLLOIDS AT INTERFACES

Colloidal particles can adsorb at liquid interfaces and be used to stabilize foams or emulsions over long period of times. Unlike surfactants, colloidal particles adsorb irreversibly at interfaces and form highly rigid layers, which can protect bubbles from coalescence or coarsening. However the adsorption dynamics of colloidal particles is very slow, wich can be an issue in foaming or emulsifying processes, where large amounts of bubbles and drops have to be generated rapidly. Indeed colloidal particles diffuse slowly to interfaces and once they touch the interface, the progression of the particles toward their equilibrium position is very slow due to pinning/unpinning of the liquid interface on nanometric defects present at the surface of the particle. Below we give two examples of experimental systems for which the adsorption dynamics can be accelerated.

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Adsorption dynamics of water/water interfaces

We have studied the adsorption dynamics of micrometric particles at a water/water interface, obtained by demixion of two incompatible polymer solutions (dextran/gelatin). The interfacial tension is of the order of 10µN/m. We found th.at the adsorption dynamics is much faster than for standard oil/water interfaces with high interfacial tensions. This is due to the fact that the pinning energy of the contact line on the particles, which directly depends on the interfacial tension, is strongly reduced. However the adsorption of gelatin pancakes on the particles, entangled with other polymer chains in the semi-dilute network, may slow down the adsorption process

PNiPAM microgels

Soft PNiPAM microgel particles are micron sized particles which can spontaneously deform as they adsorb at liquid interfaces. The adsorption dynamics of such particles is therefore very fast. We study the link between the conformation of the particles at interfaces and the stability of the corresponding liquid interfaces and how this depends on the cross-linking density, hence softness of the particles. Studying the drainage of thin liquid films made with microgel solutions, we are able to deduce the conformation of the particles at the films interfaces. We also can learn whether the particles form a bridged monolayer or a stable bilayer. We find that the softest particles tend to spread at low concentrations while they form dense layers at high concentration in which the particles stretch perpendicularly to the interface, which stabilize the films against rupture.

  • Influence of concentration and cross-linking density on the drainage of thin-liquid films containing microgels, L. Keal, V. Lapeyre, V. Schmitt, V. Ravaine, C. Monteux*, Soft Matter, 13(1), 170-180 (2017)
  • « Tracking the interfacial dynamics of PNiPAM soft microgels particles adsorbed at the air–water interface and in thin liquid films », Y. Cohin, M. FIsson, K. Jourde, GG. Fuller, N. Sanson, L. Talini, C. Monteux*, Rheologica Acta, 2013, Invitation to the special issue « Novel trends in Rheology »
  • Poly(N-isopropylacrylamide) Microgels at the Oil-Water Interface:Interfacial Properties as a Function of Temperature”, C. Monteux*, C. Marlière, P. Paris, N. Pantoustier, N. Sanson, P. Perrin, Langmuir, 26, 13839 (2010)

REACTIVE WETTING

The wetting dynamics of a drop on a substrate depends the flow and dynamics occuring at the scale of a few nanometers at the contact line between the solid and the drop. We study situations, inspired from industrial applications, where a mass transfer, caused by evaporation or substrate dissolution, occur very close to the contact line, which induces local variations of the viscosity or interfacial tensions, and modifies the wetting dynamics.

Wetting of soluble substrate

When a droplet spreads on a hydrophilic polymer film, the contact angle is not zero, as a dry polymer always present hydrocarbon moities at the air-solid interface. However, as the water drop spreads, water evaporating from the drop, diffuses into the film and hydrates it. The content of water in the film depends on the contact line velocity and thickness of the polymer film and controls the dynamic contact angle. In the case where the film is composed of a charged polymer, a gradient in osmotic pressure is created at the contact line, which can lead to the pinning of the contact line.

Publications

  • Tay, A., Bendejacq, D., Monteux, C. & Lequeux, F. How does water wet a hydrosoluble substrate, Soft Matter 7, 6953 (2011).
  • Tay, A., Monteux, C., Bendejacq, D. & Lequeux, F. How a coating is hydrated ahead of the advancing contact line of a volatile solvent droplet. Eur. Phys. J. E (2010) doi:10.1140/epje/i2010-10662-7.
  • Monteux, C., Tay, A., Narita, T., De Wilde, Y. & Lequeux, F. The role of hydration in the wetting of a soluble polymer. Soft Matter 5, 3713 (2009).
  • Tay, A., Lequeux, F., Bendejacq, D. & Monteux, C. Wetting properties of charged and uncharged polymeric coatings—effect of the osmotic pressure at the contact line. Soft Matter 7, 4715 (2011).
Wetting and evaporation

When a droplet containing colloidal particles is evaporating, the high rate of evaporation at the contact line and pinning of the contact line by the particles causes the accumulation of the solute at the contact line and to the formation of rings of colloids at the periphery of the drop. We have investigated the coupling between the pinning of the contact line and the evaporation flux in diverse situations. In the case of bidisperse colloidal dispersions, the small particles tend to segregate at the contact line. In the case of polymers solutions, the accumulation of polymer at the contact line induces a viscosity increase in the few nanometers close to the contact line, which controls the dynamic contact angle. As a consequence the dynamic contact angle depends on the relative humidity. We are now investigating the case of evaporating thin films of surfactant solutions, where additional Marangoni flows can either destabilize or stabilize the films, depending on the adsorption dynamics of the surfactants.

Collaborations – F. Lequeux (ESPCI), M. Doi, A. Crosby (U Mass), S. Deville (ILM Lyon), A. Antkowiak (Sorbonne Université)

Publications

  • Noirjean, C., Marcellini, M., Deville, S., Kodger, T. E. & Monteux, C. Dynamics and ordering of weakly Brownian particles in directional drying. Phys. Rev. Mater. 1, (2017).
  • Liu, Y., Lee, D. Y., Monteux, C. & Crosby, A. J. Hyperbranched polymer structures via flexible blade flow coating. J. Polym. Sci. Part B Polym. Phys. 54, 32–37 (2016).
  • Monteux, C. &Lequeux, F. Packing and Sorting Colloids at the Contact Line of a Drying Drop. Langmuir 27, 2917–2922 (2011)
  • Monteux, C. & Lequeux, F. Packing and Sorting Colloids at the Contact Line of a Drying Drop. Langmuir 27, 2917–2922 (2011)
  • Kajiya, T., Monteux, C., Narita, T., Lequeux, F. & Doi, M. Contact-Line Recession Leaving a Macroscopic Polymer Film in the Drying Droplets of Water−Poly( N , N -dimethylacrylamide) (PDMA) Solution. Langmuir25, 6934–6939 (2009)
  • Monteux, C., Elmaallem, Y., Narita, T. & Lequeux, F. Advancing-drying droplets of polymer solutions: Local increase of the viscosity at the contact line. EPL Europhys. Lett.83, 34005 (2008)

PHOTORESPONSIBLE SURFACTANTS, LIQUID FILMS AND FOAMS

We have shown that the adsorption/desorption dynamics of photoresponsive surfactants depends on their cis-trans conformation. We have used this property to control Marangoni flows in thin liquid films and control the stability of aqueous foams.

  • Chevallier, E. et al. Pumping-out photo-surfactants from an air–water interface using light. Soft Matter 7, 7866 (2011).
  • Chevallier, E., Monteux, C., Lequeux, F. & Tribet, C. Photofoams: Remote Control of Foam Destabilization by Exposure to Light Using an Azobenzene Surfactant. Langmuir 28, 2308–2312 (2012).
  • Chevallier, E., Saint-Jalmes, A., Cantat, I., Lequeux, F. & Monteux, C. Light induced flows opposing drainage in foams and thin-films using photosurfactants. Soft Matter 9, 7054 (2013).
  • Mamane, A., Chevallier, E., Olanier, L., Lequeux, F. & Monteux, C. Optical control of surface forces and instabilities in foam films using photosurfactants. Soft Matter 13, 1299–1305 (2017).