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The present study investigates the effects of very low concentrations of polypropylene glycol (PPG) on the rheological properties of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) aqueous solutions at the surface for the precise control of foam properties. Langmuir trough experiments and Brewster angle microscopy (BAM) of the AOT monolayer on the surfaces of PPG aqueous solutions indicated that a very low concentration of PPG increased the number of AOT molecules at the surface. Viscoelastic behaviors at the surface and surface tension isotherms in mixed aqueous solutions of AOT and PPG revealed that AOT interacted with PPG in the surface and bulk phase. A modified Ross−Miles method was performed to assess the foam stabilities of AOT aqueous solutions with and without PPG. The stabilization of foam by PPG was attributed to the rheological properties of AOT aqueous solutions at the surface.

This study investigated the relationship between the air–water interfacial dilational viscoelasticity and foam properties in mixed anionic surfactant aqueous solutions of sodium bis(2-ethylhexyl)sulfosuccinate (AOT), sodium n-dodecylsulfate (C12AS), sodium n-tetradecylsulfate (C14AS), and sodium n-hexadecylsulfate (C16AS). The surfactants used here differ only in hydrophobic chains. The air–water interfacial viscoelasticity of AOT aqueous solutions mixed with C12AS or C14AS was similar to that of AOT single aqueous solutions at the same constituent concentration of AOT. On the other hand, the air–water interfacial viscoelasticity of mixed aqueous solutions of AOT and C16AS was intermediate between the respective single aqueous solutions. The foam properties of these mixed aqueous solutions were evaluated by a modified Ross–Miles method and it was shown that foam stability is correlated with the maximum value of viscoelastic modulus in mixed aqueous solutions of AOT and AS.