NMR spectroscopy was used to investigate whether limonene, a typical fragrance molecule, incorporates itself into the micellar structure of zwitter-ionic and ionic surfactants. Specifically, Diffusion-Ordered-Spectroscopy (DOSY) was used to determine the concentration and temperature dependent diffusion coefficients of all components of aqueous surfactant/limonene solutions. These diffusion coefficients were then coupled with viscosity data to determine the aggregate radii of each component in the mixtures. Surprisingly, the limonene molecules were found to be aggregating independently of the surfactant micelles, with radii that are highly temperature dependent. Additional T1 and T2 relaxation studies were also performed in which the restriction to motion of the hydrophobic surfactant tails was found to increase with temperature. The combined results suggest the presence of equilibrium between two types of aggregates, one rich in surfactant, one rich in limonene. In the case of the zwitter-ionic surfactant, an increase in temperature appears to cause a gradual break-up of the two aggregates into the formation of one single, smaller-sized aggregate.
|Presenter:||Carl Schrader (Undergraduate Student)|
|Time:||11:05 am (Session II)|