Interfacial and wetting behavior of natural–synthetic mixed surfactant systems

Abstract

Interfacial and wetting behavior of a double chain cationic synthetic surfactant di-dodecyldimethyl ammonium bromide (DDAB), a natural surfactant (Shikakai), and their mixtures of five different ratios have been studied by surface tension and dynamic contact angle measurements. Pure Shikakai has higher surface tension and contact angle values at critical micelle concentration (CMC) than DDAB, indicating that it is inferior to DDAB and also commonly used synthetic surfactants. Addition of DDAB to Shikakai gives a gradual lowering of the CMC, surface tension and contact angle values at the CMC. When the concentration of DDAB is ∼50 mol% the final surface tension and contact angle values are very close to those of pure DDAB. The mixed surfactant solutions show strong non-ideal solution behaviour because of the interaction between the two surfactants. As the wetting properties of a natural surfactant are enhanced in the presence of a synthetic surfactant, the use of plant–synthetic mixed surfactant systems may be useful in wetting and in several other applications. At the same time the consumption of synthetic surfactant can also be reduced.