Foam properties and stabilizing mechanism of sodium fatty alcohol polyoxyethylene ether sulfate-welan gum composite systems

Foam properties of the anionic–nonionic surfactant sodium fatty alcohol polyoxyethylene ether sulfate (AES) and microbial polysaccharide welan gum composite systems have been investigated. Both foaming ability and foam stability of AES/welan gum composite system are better than for either single component. It is important to control the quantities of the two species when to use, since there exist optimum foaming concentrations for AES (1000 mg L−1) and welan gum (80 mg L−1). Competitive adsorption exists between AES and welan gum at the air/liquid interface. A network structure is formed in the AES/welan gum composite system as the dynamic modulus has exponential relationship with the concentration. High interfacial elasticity is required to prevent the coalescence of the bubbles and the rupturing of interfacial layers. The hydrogen bonds and van der Waals forces between AES and welan gum may hinder AES molecules from diffusing from the bulk to the interface. The formation of an interface network of welan gum and the structural stability of double helices, arranged in parallel as zipper model within the network, strengthen the ability of the film to resist disturbance and deformation.