Speaker
Description
In recent years, biosurfactants have been sparking increasing interest in both, academic research and industry, as an alternative to conventional, petrochemical-derived surfactants. From an application point of view, the use of biosurfactants allows for more biocompatible formulations that are also less harmful to the environment, due to a lower $\mathrm{CO_2}$ footprint in production and their enhanced biodegradability. Their aggregation behaviour and interfacial activity in solution, however, is far from being fully understood and often depends on a multitude of parameters, e.g. pH, ion concentration or temperature. Rhamnolipids, a class of glycolipids that is produced by microorganisms, are among the most thoroughly researched biosurfactants [1,2]. In our current research, we are focussing on biocompatible microemulsion formulations, which are an interesting basis for, e.g. cosmetic or detergent applications due to their ultralow interfacial tension between water and oil phases and excellent wetting properties. in the quaternary system $\mathrm{H_2O}$ – Isopropylmyristate (IPM) – di-Rhamnolipid ($\mathrm{Rha_2C_{10}C_{10}}$) – Octane-1,2-diol, where IPM is used as nonpolar oil phase, while Rha2C10C10 and octanediol serve as surfactant and hydrophobic co-surfactant respectively. The use of a co-surfactant allows to tune the composition of the interfacial film, which is a key parameter to influence its curvature, allowing to drive a system through phase inversion from oil-in-water to water-in-oil microemulsions via the balanced, bicontinuous morphology [3].
Having extensively studied the phase behaviour of these quaternary microemulsions, we recently had the opportunity to carry out contrast variation SANS experiments with the goal to investigate the composition of the interfacial film at different temperatures. To this end, we first used deuterated IPM to reach film contrast conditions (i.e. a contrast matching of the aqueous and oil phase) and subsequently d-octanediol to reach a rhamnolipid contrast (matching of the aqueous, oil, and octanediol components). To our surprise, we found an untypical scattering behaviour at high q, pointing towards an uneven distribution of $\mathrm{Rha_2C_{10}C_{10}}$ molecules in the amphiphilic film or a very defined conformation of the rhamnolipid’s double sugar head group. Our results highlight the power of contrast variation SANS in the study of novel surfactants and how it needs to be coupled with other studies, such as molecular dynamics or high-resolution NMR to understand the complex interfacial aggregation behaviour of this important class of biosurfactants.
[1] N. Baccile et al. Langmuir 2023, 39 (27), 9273-9289.
[2] P. Le Bastart de Villeneuve, F. Trummer et al. J. Mol. Liq. 2025, 436, 128271.
[3] R. Strey, M. Jonströmer J. Phys. Chem. 1992, 96(11), 4537-4542.