Adsorption and dilational rheology of polyacrylamide at interfaces: Implication on the stability of polymer-containing foamulsions

Understanding and developing a stable oil-laden foam (foamulsion) with targeted properties is important for many industrial applications including mineral flotation and resource recovery. In this work, the adsorption and interfacial viscoelasticity of polyacrylamide (PAM) and Triton X-100 (TX100) systems at the oil–water and air–water interfaces were investigated using dynamic tensiometry and dilational rheology measurements. For comparison, the TX100-alone systems were also examined at identical conditions. Pentane and dodecane were employed as representative oils. Dynamic surface/interfacial tension data for both mixed TX100/PAM and TX100-alone solutions could be well described by an empirical kinetic model. Although PAM itself in water was interface-inactive, the presence of TX100 surfactant with an onset concentration or above would induce the adsorption of PAM into the interfaces, as indicated by slower adsorption kinetic constant and higher viscoelastic moduli. A more concentrated surfactant in water was required for the oil–water interface than that for the air–water interface to trigger a significant impact of PAM on dynamic tensiometry and dilational viscoelasticity data. In addition, foam height decay profiles in oil–water mixture at two surfactant concentrations with or without PAM were monitored, from which the stability of foamulsion was quantified by foam half-life. It was found that at a low surfactant concentration, PAM had a negligible influence on the stability of foamulsions. However, PAM boosted the stability of foamulsions at relatively higher surfactant concentration (0.06 wt%), regardless of solvent types and contents. Correlation of foamulsion stability with interfacial tension and dilational viscoelasticity data is discussed.