Rhamnolipids are of current interest as greener alternatives to common synthetic surfactants. However, little is known about the fundamental aggregation properties of these surfactants. To better understand these aggregation properties, surface tensiometry, dynamic light scattering, and static and time-resolved fluorescence spectroscopy were applied to aggregates formed from the native monorhamnolipid mixture produced by Pseudomonas aeruginosa ATCC 9027 and to aggregates formed from all possible stereoisomers (R,R; R,S; S,R; and S,S) of the most common naturally-occurring monorhamnolipid congener, Rha-C10-C10. For concentrations above the critical micelle concentration (CMC) of ~180 �M at pH 8, globular micelles of ~2-3 nm predominate along with two other minor aggregates, likely bilayers and vesicles, with dimensions of ~12 and ~140 nm, respectively. Monorhamnolipid micelles were further probed in fluorescence quenching studies with pyrene as the probe and benzophenone to determine average aggregation number (Nagg) of these aggregates. Micelles from these monorhamnolipids have N-agg- valuesof ~30-35 molecules.

Aggregation characteristics of rhamnolipid biosurfactants and several synthetic variants

247th National Meeting (2014)

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