title: Photofoams: remote control of foam destabilization by exposure to light using an azobenzene surfactant.
abstract: We report evidence for photocontrolled stability and breakage of aqueous foams made from solutions of a cationic azobenzene-containing surfactant over a wide range of concentrations. Exposure to UV or visible lights results in shape and polarity switches in the surfactant molecule, which in turn affects several properties including critical micelle concentration, equilibrium surface tension, and the air-water interfacial composition (cis isomers are displaced by trans ones). We demonstrate that the trans isomer stabilizes foams, whereas the cis isomer forms unstable foams, a property that does not correlate with effects of light on surface tension, nor with total surfactant concentration. Achieving in situ breakage of foam is accordingly ascribed to the remote control of the dynamics of adsorption/desorption of the surfactant, accompanied by gradients of concentrations out of equilibrium. Photomodulation of adsorption kinetics and/or diffusion dynamics on interfaces is reached here by a noninvasive clean trigger, bringing a new tool for the study of foams.
authors.affiliation: Laboratoire de Sciences et Ingénierie de la Matière molle (PPMD-SIMM), CNRS-UMR 7615, ESPCI, 10 rue Vauquelin, 75005 Paris, France.
authors.forename: E
authors.initials: E
authors.lastname: Chevallier
authors.forename: C
authors.initials: C
authors.lastname: Monteux
authors.forename: F
authors.initials: F
authors.lastname: Lequeux
authors.forename: C
authors.initials: C
authors.lastname: Tribet
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D008027:Light; D015394:Molecular Structure; D055668:Photochemical Processes; D013500:Surface Tension; D013501:Surface-Active Agents / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: D001391:Azo Compounds; D013501:Surface-Active Agents; C009850:azobenzene