Effect of isomer distribution on the self-assembly properties of alkylbenzene sulfonate surfactants

The self-assembly behaviour of alkylbenzene sulfonate surfactants (LAS), widely used as components for detergent formulations, is strongly influenced by the molecular structure of their hydrophobic tail and the distribution of its isomers. For instance, largely different behaviour has been observed in measurements of dynamic surface tension of different pure isomers or their mixtures. The surface activity varies across different mixture ratios and for the single components, indicating possible synergistic interactions at the interface and/or in bulk aggregation. The isomeric composition determines the surfactant properties, which points to the need for systematic studies that directly correlate specific isomer distributions with aggregate structure and function. Accordingly, we are interested to learn in detail how the aggregate structure and size may relate to the adsorption dynamics of the LAS, as well as their general property profiles. SANS in D2O shall allow to see the structural features in sub-nm resolution and to determine how the aggregate structure is controlled by the molecular architecture of the surfactants and their overall concentration. The obtained data will be analysed quantitatively by model fitting to different micellar structures such as polydisperse spheres or ellipsoidal micelles. From this we will be able to generate a generalised picture of how the structure of the LAS translates into its aggregation behaviour and also controls other properties.