Experimental investigation of the acoustic properties of liquids foams

Abstract

International audienceLiquid foams are mixtures of gas and liquid, with a liquid volume fraction $\phi _{l} {\leq}0.3$, stabilized with surfactants. Because of their composition and structure, liquid foams are very complex and unstable media with particular acoustical properties. Experimental studies are not very numerous; they have shown a strong dependence of the velocity and attenuation of sound on parameters such as $\phi _{l}$ and the average bubble size [1]. The existent theories explain a part of the acoustic behaviour of liquid foams, but are not exactly in accordance with the experimental data found in the literature. For example, the experimental phase velocities [Phys. Rev. E 66 (2002) 021404] are larger than the velocities predicted by the Wood approximation [A. B. Wood, A Textbook of sound (Bell, London, 1932)]. We present an experimental investigation of liquid foams by an ultrasonic setup based on two broadband air transducers (40-200kHz). The acoustic properties are deduced from the reflected signal. We discuss experimental results with commercial (shaving foams) and custom-made controlled foams and compare them with available models. The evolution of the acoustic properties with the aging of the foams is also discussed