Dynamic Stabilization of Foam Films with Acoustic Sound.

Abstract

This paper demonstrates the stabilization of single foam films at dynamic conditions induced by exposure to the acoustic sound. The foam films were formed from aqueous solutions using a Sheludko cell. In the presence of sound at certain sound frequencies and above certain thresholds of sound amplitude, the lifetime of the film with 1 × 10-4 M sodium dodecyl sulfate (SDS) in the presence of 0.1 M NaCl was significantly increased, and a stabilization map was drawn to show the three levels of film stability (i.e., unstable, metastable, and stable) obtained over a broad range of sound frequencies (1-19 kHz) and amplitudes (74-125 dB). In particular, stable films were observed at relatively high frequencies (14-19 kHz) and high amplitudes (>107 dB) and metastable films were observed at intermediate frequencies (8.8-9.3 kHz) and high amplitudes (>111 dB). The stabilization effect was also demonstrated with different surfactants at different concentrations, at different electrolyte concentrations (in the presence and absence of the surfactant), and at different temperatures. Image analysis suggested the presence of liquid flow within the films that were stabilized by exposure to the acoustic sound. The stabilization effect could be attributed to the hydrodynamic pressure arising at dynamic conditions.