Rhamnolipids are a form of glycolipid, and in the context of applications are of the more promising biosurfactants as they are produced in relatively large quantity by the microorganism pseudomonas. The rhamnolipids produced are in the form of mixtures of two major types, mono-rhamnolipid (Rha-C10-C10, R1) and di-rhamnolipid (Rha-Rha-C10-C10, R2). In this study, small angle neutron scattering (SANS) was used to investigate the size and morphology of rhamnolipid aggregates. SANS results of unseparated rhamnolipids mixtures indicate coexistence of planar and globular structures. For all the concentrations measured for R1, the SANS data show q-2 dependence, which indicates the formation of planar (lamellar/vesicle) structures. The SANS data for R2 are consistent with the formation of globular micelles. The effect of Ca2+ ions on the self-assembly were also studied and it was found that Ca2+ results in a tendency towards more planar structures.

Krafft points were measured for various mixtures containing different compositions of R1 and R2. The results showed a very interesting synergistic effect between R1 and R2 in terms of Ca2+ tolerance. That is, R1 by itself has a Krafft point of 86 °C in presence of 4mM Ca2+, but under the same condition, the Krafft point of 90:10=R1:R2 was only 11°C. Furthermore, Krafft points of composition consisting 20% and above of R2 were consistently below 0°C. The surface tension of R1, R2 and their mixtures of different composition were measured and appeared to show close to ideal mixing behaviour. These preliminary results indicate the presence of some interesting synergistic features of rhamnolipid and rhamnolipid mixtures.