Structure of Urea Clusters Confined in AOT Reversed Micelles

Abstract

The structure of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and that of urea containing AOT reversed micelles has been investigated by small-angle neutron scattering (SANS) and Fourier transform infrared (FT-IR) spectroscopy at different AOT concentrations and urea/AOT molar ratios. For the AOT/n-heptane system, SANS data analysis indicates that AOT molecules form prolate ellipsoidal aggregates, which grow asymmetrically along the major axis upon increasing the surfactant concentration. For the urea/AOT/ n-heptane system, the SANS results are consistent with the hypothesis that urea is encapsulated as small-sized ellipsoidal hydrogen-bonded clusters within the hydrophilic micellar core of the AOT reversed micelles. The insertion of urea in the micellar core causes a significant increase of the aggregate size along the minor-axis direction. FT-IR data indicates that, quite independently from the urea and AOT concentrations, the encapsulation of urea clusters in the AOT micellar core involves some changes of the H-bonded structure characterizing pure solid urea. This structural change was rationalized in terms of the specific interactions between the urea NH2 and the AOT SO3groups in small-sized urea clusters. Moreover, the CO stretching mode analysis suggests that within the cluster the urea CO groups interact with the urea NH 2 groups whereas the AOT CO groups do not.

Highly viscous wormlike micellar phases formed from the mixed AOT/C14DMAO/H2O system

“…Most studies focused on the reverse structures of AOT with different counterions (Na + , Ag + , Ca 2+ , Ni 2+ , Al 3+ , and In 3+ ) and their use in synthesizing nanomaterials [36][37][38][39][40][41]. However, the results in aqueous solutions are considerably less than those in nonaqueous solutions.…”

Temperature-induced percolation behavior of AOT reverse micelles affected by poly(ethylene glycol)s

“…Over the last few decades increased interest has been established in assimilating various additives varying from inorganic compounds, biological molecules to the polymeric structures, within the core of the microemulsion systems [5][6][7][8][9]. Moulik et al [10][11][12] studied the effect of sodium cholate, salicylate and various hydrotopes (viz.…”

Mixed anionic and zwitterionic surfactant based microemulsions as vehicles for solubilizing organodiselenides

“…The high frequency values observed in ME-II as compared to ME-I reveal the entrapping of organodiselenide in the micellar interface. The results further depict the presence of specific interactions between the interfacial water molecules and the organodiselenide moieties [35]. The presence of organodiselenides perturbs the H-bonding capabilities of the OH, CO and C-O-C groups of the surfactant molecules.…”