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Spontaneous oil suction by dry aqueous foams
Detergency, food products, fire fighting or enhanced oil recovery are diverse examples that involve both aqueous foam and oil. Indeed, when using appropriate surfactants, oil and aqueous foam can be intimately mixed without destroying the foam. In most of the experimental studies concerning oils and foams, oil is first emulsified in a surfactant solution by vigorous stirring. Then, the oil-laden foam is obtained by sparging air in the emulsion. We show that oil laden foam can also be obtained using the capillary depression that naturally prevails in dry foam and demonstrate that dry foams can be used to draw and transport oil volume even if the oil is initially confined. Using surface evolver simulations and both local and global scale experiments, we review the thermodynamics criteria to observe oil spontaneous imbibition in foam. Then, we emphasize the oil imbibition dynamics, and its interplay with the ageing dynamics of foam. We propose a comprehensive understanding to rationalize our findings.