Angelita Rita Krama1,2, Yanic Paprotny1,3, Prof. Dr. Cosima Stubenrauch2, Dr. Peter Schmiedel1, Prof. Dr. Michael Schmitt3

1 LRR-Material Science, Henkel AG & Co. KGaA, 40589 Düsseldorf, Germany
² Universität Stuttgart, Institut für Physikalische Chemie, Pfaffenwaldring 55, D-70569 Stuttgart
3 Heinrich-Heine-University, Universitätsstraße 1, 40225, Düsseldorf, Germany

Traditional laundry, home‑, and personal‑care formulations frequently rely on synthetic, petroleum‑derived surfactants. To move toward more sustainable product architectures, surfactants from renewable microbial sources offer a promising path. Mannosylerythritol lipid B (MEL‑B, predominantly C15) is a microbial glycolipid with strong hydrophobicity, high affinity for oils and fats, and excellent interfacial activity. However, MEL‑B alone is too hydrophobic and has limited water solubility, which restricts its performance in cleaning applications. Its packing parameter, close to unity, leads to the formation of bilayers and vesicles rather than highly curved aggregates required for efficient solubilization.
To tune curvature and enhance functionality, we combine MEL‑B with rhamnolipid (RL, C10–C10), a more hydrophilic biosurfactant that forms spherical micelles. By blending both amphiphiles, the curvature of the mixed interfacial film can be systematically controlled, enabling access to structures relevant for formulation science and cleaning performance.
We investigate the physicochemical properties and phase behavior of MEL‑B/RL mixtures using ring tensiometry, spinning‑drop tensiometry, maximum bubble pressure tensiometry, dynamic light scattering, rheology, polarized light microscopy, small‑angle X‑ray scattering, and optical phase analyses. These complementary techniques elucidate the impact of the mixtures on air/water and oil/water interfacial properties as well as on aggregation kinetics.
Our results show that MEL‑B/RL mixtures significantly modify the curvature and packing of the amphiphilic film. The RL phase diagram reveals a transition from an isotropic to a hexagonal phase, while the ternary MEL‑B/RL/water system shifts from spherical aggregates toward lamellar structures. These findings demonstrate that even small amounts of MEL‑B effectively reduce curvature and promote flatter interfacial arrangements.
Overall, MEL‑B/RL mixtures provide a renewable, tunable surfactant system with adjustable curvature, interfacial properties, and phase behavior—supporting the development of more sustainable consumer‑care formulations.