Surfactant-surfactant molecular interactions in mixed monolayers at a highly hydrophobic solid/aqueous solution interface and their relationship to enhanced spreading on the solid substrate

Spreading of mixed aqueous hydrocarbon-chain surfactant solutions on the solid polyethylene (PE) surface has been studied. Synergistic effect on the spreading of the mixed surfactant solution on the PE film has been observed, and the obtained spreading is comparable to superspreading normally obtainable from trisiloxane-based surfactants. Some other interfacial phenomena related to surfactant spreading, such as surfactant-surfactant molecular interactions in the mixtures adsorbed at various interfaces, dynamic contact angle change of the mixed surfactant solutions during the process of spreading on the hydrophobic PE substrate, and surfactant adsorption at the solid/liquid and air/liquid interfaces have been investigated. It is suggested that stronger surfactant-surfactant attractive interactions and greater adsorption at the PE powder/aqueous solution interface than at the air/aqueous solution interface account for the observed spreading enhancement in the mixed hydrocarbon-chain surfactant systems, which is also accompanied by lower dynamic contact angles, implying greater dynamic spreading coefficients.