We have studied concentrated phases of Aerosol OT (AOT) in polar (water, ethylene glycol, formamide, N,N-dimethylformamide) and apolar (isooctane) solvents. We investigated two surfactant volume fractions (φ = 0.2 and φ = 0.6) with small angle x-ray scattering (SAXS), rheology and electrical conductivity experiments. AOT self-assembles differently depending on solvent type and concentration. SAXS experiments show that the AOT/water system displays a lamellar phase. In the other cases, only formamide displays a lamellar phase for φ = 0.6. The other solvents (and formamide at φ = 0.2) promote the self-assembly of AOT in other microstructures. The SAXS spectra display correlation peaks consistent with a disordered array of cylindrical aggregates. The microstructure of the AOT/isooctane system at φ = 0.2 is that of an arrangement of spherical aggregates. The results are explained in terms of surfactant packing models and solvent properties. For instance, the ability of ethylene glycol to form hydrogen bonds with AOT promotes the formation of cylindrical aggregates by increasing the area per surfactant polar head. As N,N-dimethylformamide is slightly miscible in hydrocarbons it increases the volume of the surfactant tail promoting reverse structures.
Bibliographical noteFunding Information:
Daniel Berrellez and Alan German Acedo‐Mendoza acknowledge financial support from the Consejo Nacional de Ciencia y Tecnología (Conacyt, Mexico). We thank the reviewers for insightful comments. We have incorporated some of their sentences in the revised manuscript. This study was partially funded by Conacyt grants 256753, 231444 and 242943.
© 2021 AOCS.
- Aerosol OT
- lamellar phase
- polar solvents