Laboratoire de Sciences et Ingénierie de la Matière molle (PPMD-SIMM), CNRS-UMR 7615, ESPCI, 10 rue Vauquelin, 75005 Paris, France.
Langmuir. 2012 Feb 7;28(5):2308-12. doi: 10.1021/la204200z. Epub 2012 Jan 27.
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.
我们报告了在广泛浓度范围内，由含有阳离子偶氮苯的表面活性剂溶液制成的水基泡沫的光控稳定性和破裂的证据。暴露于紫外或可见光下会导致表面活性剂分子的形状和极性发生转变，这反过来又会影响包括临界胶束浓度、平衡表面张力和空气-水界面组成在内的多种性质（顺式异构体被反式异构体取代）。我们证明反式异构体稳定泡沫，而顺式异构体形成不稳定的泡沫，这种性质与光对表面张力的影响无关，也与表面活性剂总浓度无关。因此，泡沫的原位破裂归因于表面活性剂吸附/解吸动力学的远程控制，同时伴有非平衡浓度梯度。通过非侵入性的清洁触发，在这里实现了对界面上吸附动力学和/或扩散动力学的光调制，为泡沫的研究带来了新的工具。
