An unusual morphological transformation of rhamnolipid aggregates induced by concentration and addition of styrene: A small angle neutron scattering (SANS) study

The aggregation behaviour of rhamnolipid as mixed with styrene (as a representative of hydrophobic molecules commonly found in contaminated soils) was investigated by small angle neutron scattering (SANS) as a function of both rhamnolipid and styrene concentrations. Contrast variation was applied (i.e., deuterated and hydrogenated styrene) to resolve the morphologies of aggregates. A structural transformation from cylindrical micelles to a binary mixture of cylindrical micelles and vesicles induced by both elevated rhamnolipid and styrene concentration is proposed based on the analysis of the SANS data. The resultant structure of the aggregates, vesicle, is different from the “oil droplets” commonly reported in the microemulsions of water-oil-surfactant mixtures. It is also found that this transformation is far from being complete even at the highest styrene solubility, implying that further dissolution of styrene may be constrained by other factors.

.Figure optionsDownload as PowerPoint slideResearch highlights▶ Increased rhamnolipid concentration initiates a micelle-to-vesicle transformation. ▶ Addition of styrene initiates the same micelle-to-vesicle transformation. ▶ The micelle-vesicle structural phase transition is not common observed in regular water-oil-surfactant systems undergoing microemulsion. ▶ Contrast variation method of SANS shows a powerful tool to identify the binary structures in a mixture. ▶ The structural transformation is not complete even at highest styrene or rhamnolipid concentrations.