We have measured the surface dilational elastic moduli of bubbles immersed in water and soap bubbles in air. The short time response was obtained by submitting the bubbles to a rapid expansion after which the surface tension evolution was monitored, using either image analysis or pressure measurements. It was possible with this method to measure directly the Gibbs elasticity. The longer time response was obtained by submitting the bubbles to low frequency oscillations. Experiments were performed with solutions of non-ionic surfactants, C 12 E 6 , C 12 G 2 , their 1:1 mixture, Pluronic F-68 and 127 and the surface elastic moduli were compared with the stability of foams made with these surfactants. The foams evolve with time, first by Ostwald ripening, controlled by the low frequency elasticity, and then by bubbles coalescence, controlled by the high frequency elasticity.

We have measured the short-time and long-time elastic responses to compression of various types of surfactant layers adsorbed at oil-water interfaces. We prepared reasonably monodisperse oil-in-water emulsions with the same surfactants and monitored the time evolution of the emulsion droplets' diameter. We used a broad variety of surfactants (cationic, nonionic, and small polymers) and alkanes with different chain lengths. The emulsion drop size evolution is first controlled by Ostwald ripening and later on by drop coalescence, the later step being quite short. The overall emulsion lifetime is therefore dominated by ripening and for a given oil appears well correlated with the low-frequency surface elasticity as expected (and not with the high-frequency one, which is expected to control coalescence). When the oil chain length is changed, the stability is related more to the oil solubility in water, which also controls ripening. The overall results demonstrate the great importance of surface elasticity in emulsion stability.