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From stimuli-responsive molecules to responsive interfaces, bubbles and foams
Over the last ten years, many advances have been obtained on the understanding of the properties of aqueous foams : for instance, regarding their stability, aging or rheology. Initially, the results were collected on model foams, made from basic surfactant solutions. More recently, we made large advances on controlling the foam properties by using new types of stabilizers or by doping the foam with soft and rigid colloidal particles. In all these cases, new behavior are observed, and effects like irreversible adsorption at interfaces and confinement-induced jamming have to be introduced. I’ll first present significant examples illustrating these effects, evidencing the links between chemical formulation and macroscopic sample properties.
Then, changing in situ the chemical formulation of a foam, by an external stimulus, to obtain efficient macroscopic reactivity is the next challenge. I will present some experiments on gas-liquid interfaces, liquid films, bubbles, gels and foams doped with stimuli-responsive molecules : these experiments allow us to investigate if a molecular stimuli-responsivity can actually be active and transposed to hierarchical macroscopic soft structures. Thanks to collaboration with chemists, we performed experiments with thermo-responsive surfactants and polymers and light-responsive surfactants. These results open many new questions : in particular, I will show how macroscopic motion, spreading and deformation can result from spatial gradients of the stimulus and from induced-Marangoni stresses.
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