Impact of Nearly Water-Insoluble Additives on the Properties of Vesicular Suspensions

Nearly water-insoluble additives are commonly used in surfactant-based consumer products to enhance their appeal or performance. We used viscosity measurements, time-resolved cryogenic transmission electron microscopy, and NMR spectroscopy to investigate the effect of several additives, linalyl acetate (LA), cyclohexanol, phenol, catechol, guaiacol, and eugenol, that have extremely low water solubility, on the evolution of microstructures in an aqueous multilamellar vesicle suspension of diethylester dimethylammonium chloride (DEEDMAC), a major ingredient in fabric softeners. LA and eugenol are used as fragrances in some detergent-related consumer products. The other additives were chosen to have degrees of aromaticity that are intermediate between LA and eugenol. The viscosity of the DEEDMAC suspension increased only marginally upon addition of LA, while it rose significantly upon addition of eugenol. Cryo-TEM revealed no observable changes to the multilamellar structures in the DEEDMAC suspension when LA was added. The addition of eugenol triggers a transition from multilamellar vesicles to predominantly unilamellar vesicles and bilayer fragments through exfoliation and breakage. By examining NMR results from all the additives, we propose that π electrons in aromatic rings interact strongly with the cationic DEEDMAC head groups. Such interactions are strong in eugenol but not present in LA.