FOAMS

Photoresponsive surfactants and photofoams

Foams, are composed of many bubbles, stabilized by adsorbed surfactant molecules. The stability of interfacial materials over time or in response to a mechanical stress depends on the adsorption/desorption dynamics of the surfactant molecules, which depends on their shape or hydrophobicity, and plays a role at various scales, ie the drainage of a thin film, the coalescence of several bubbles… To understand and control the stability of interfacial materials, we used « photosensitive » surfactants which hydrophobicity can be tuned with UV or Blue illumination and we track the interfacial response from the microscopic to the macroscopic scale. Azobenzen surfactants, which have a trans- conformation a rest, can isomerize into their cis trans when illuminated under blue or UV light, which induces a modification of their polarity: cis-isomers are more polar and surface active than the trans isomers. A modification of the surfactant’s polarity can have surprising consequences at the mesoscopic scale (thin films) and macroscopic scale (foams). Collaboration : C. Tribet (ENS), F. Lequeux (ESPCI), I. Cantat (IP Rennes), A. Saint-Jalmes (IP Rennesà Publications

• Chevallier, E. et al. Pumping-out photo-surfactants from an air–water interface using light. Soft Matter 7, 7866 (2011).
• 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).
• 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).
• 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).

Highly stable foams made with 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. Producing stable foams from highly viscous fluids is a challenge : during the foaming process, the high viscosity prevents incorporation of gas bubbles into the viscoelastic matrix. We investigate the role of rheological properties of the continuous phase on the foaming process with a special interest in shear thinning and yield stress fluids or dilute suspensions in which aggregates can break upon shear and reform at the interface.

• Deleurence, R., Saison, T., Lequeux, F. & Monteux, C. Time scales for drainage and imbibition in gellified foams: application to decontamination processes. Soft Matter11, 7032–7037 (2015).
• Deleurence, R., Saison, T., Lequeux, F. & Monteux, C. Foaming of Transient Polymer Hydrogels. ACS Omega3, 1864–1870 (2018).
• P24. 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)