Nanoconfinement of Water Layers in Lamellar Structures Prepared in the Presence and Absence of Organic Solvent

Abstract

An attempt is made to draw a line of comparison between the extent of rigidity of the hydration layers bound to the interfacial region of lamellar structures of Aerosol OT (AOT, sodium bis(2-ethylhexyl) sulfosuccinate) in water, in the presence and absence of an organic solvent using POM, SAXS, cryo-TEM, and time-resolved fluorescence spectroscopy. These systems are ternary mixtures of AOT, water, and n-heptane containing lamellar structures in an aqueous layer at higher w(0) values (w(0) = 300 and 150) and a binary solution of 20 and 50% AOT in neat water (w/w). The solvation shells residing at the vicinity of these lamellar structures are monitored using two different coumarin probes (C153 and C500). It is intended to envisage a comparative solvation dynamics study of the restricted aqueous region confined in lamellar structures formed in ternary mixture and binary solution. Though steady state measurements show a similar microenvironment probed by the fluorophores in lamellar structures formed in the two different aqueous phases, temporal evolution of the solvent correlation function C(t) unveils the existence of lamellar structures with different degrees of confinement of water layers in these two systems. A slower relaxation of the restricted aqueous region in lamellar structures of binary solution signifies the presence of more rigid interfacially bound water layers at the lamellar interface than in the ternary mixture having a similar weight percentage of AOT in water. The present investigation concludes that the lamellar structures formed under two different conditions provide a similar hydrophobic environment with different extents of localized water populations at the lamellar interface as manifested by the solvent relaxation time in agreement with SAXS and cryo-TEM images.