The influence of bilayer fluidity on the stability of aqueous foams made from surfactant vesicle dispersions

Abstract

The structures formed by surfactant self-assembly in bulk can affect the surface properties of the resulting solutions, thus impacting foam formation and stability. Bilayer fluidity in surfactant vesicle dispersions is expected to influence molecular packing at the surface and the viscosity of the continuous phase, thereby affecting the quality of the aerated dispersions. Hence, it should be possible to control foam characteristics by tuning the surfactant organization within bilayers. In this work, surfactant vesicle dispersions were prepared in the presence of an unsaturated fatty alcohol, at different concentrations, used to induce variations in bilayer fluidity at room temperature. A variety of experimental techniques was employed to characterize both bulk and surface properties of the vesicle dispersions and the resulting foams prepared by the hand-shaking method. It was seen that added fatty alcohol reduced the packing of surfactant in the bilayers. All tested dispersions presented similar foaming ability, although foams produced from vesicles with highly ordered surfactant chains were remarkably more stable, making this the first direct evidence of bilayer fluidity impact on foam stability. Such an enhanced stability was attributed to the formation of a dense surfactant film at the surface of the bubbles and to the low rate of liquid drainage in the foams, thus opening new possibilities of accurately controlling foam stability in products in which surfactant vesicles can be found.