Structure-dependent interfacial behavior of bioinspired glycolipid surfactants

Abstract

Surfactants continue to find expanding applications in areas such as environmental remediation, consumer product formulation, and textile processing; however, their petrochemical origin and associated environmental toxicity remain significant concerns. As a result, considerable effort has been directed toward the development of “green” surfactants, which are naturally derived and exhibit reduced toxicity while maintaining the functionality of conventional surfactants. Glycolipids, a class of bacterially derived surfactants composed of a sugar headgroup and alkyl tail, represent a promising subset of these materials with potential in applications such as environmental remediation and wastewater treatment, agriculture, aqueous mining, cosmetics, and detergents. Traditionally, glycolipids are produced by Pseudomonas aeruginosa as mixtures of mono- and dirhamnolipids with alkyl chains containing 10 carbons. However, recent advances in synthetic chemistry have enabled the production of single congeners and systematic variation of both headgroup composition (e.g., rhamno-, xylo-, and galactolipids) and alkyl chain length. The interfacial properties of these materials have not been comprehensively characterized. Here, we report a systematic evaluation of the surface and interfacial properties of a series of newly synthesized glycolipids. These compounds exhibit significantly lower critical micelle concentrations than sulfate surfactants of comparable alkyl chain length, while maintaining similar minimum surface tension values. This indicates that glycolipids retain comparable effectiveness while offering substantially greater efficiency. Variations in headgroup identity produce minimal changes in interfacial behavior, whereas alkyl chain length and tail architecture (single vs. double) have a pronounced impact. Together, these results elucidate structure–property relationships governing interfacial behavior and provide a foundation for the development of applications leveraging these green surfactants.