Mechanistic Insights into Mixed Surfactant-Biosurfactant Self-Assembly, Rheology and Surface Properties

The global surfactant market is expected to reach $44.9 billion by 2022, of which 67% of the demand is from the personal care and detergents market. Due to consumers’ increasing awareness on product sustainability, the microbially produced biosurfactants are increasingly gaining the interest of the personal care industry as potential alternatives for traditional petroleum derived and chemically synthesized surfactants. However, prior to that, an understanding of how performance criteria such as rheology and interfacial properties are affected by substitution of traditional surfactants with biosurfactants is required. In this study, the effect of rhamnolipid and sophorolipid biosurfactants on the rheological response and interfacial properties of traditional surfactants such as sodium laureth sulfate and cocamidopropyl betaine is explored utilizing a range of advanced characterization techniques. Diffusing Wave Spectroscopy based Optical Microrheology is specifically carried out to gain insights into the short time dynamics in these systems and is also utilized for extracting wormlike micelle structural parameters such as contour lengths and persistance lengths. These insights are utilized to develop unique formulation design rules for biosurfactant based products.