Confinement effects on water structure in membrane lyotropic phases

The change of the water structure in aqueous solutions of the tri-ethyleneglycol mono n-decyl ether (C10E3) was studied by micro Raman scattering. The results obtained on the O–H stretching band show that the behavior of the hydrogen bonding (H-bonds) water network can be used as a probe to follow the lamellar (Lα) to sponge (L3) phase transition. In the lamellar phase, the stack of the surfactant molecules aggregated into a two-dimensional structure (membrane) acts as a soft confinement system for the H-bond water network of which the regular tetrahedral structure is perturbed. The change of the planar organization of the membranes to a highly disordered and infinite array of bilayers in the sponge phase amplifies the surface of contact between amphiphilic surfactant and water molecules which drives a strong disruption of the regular tetrahedral H-bonding water network.

ROH parameter, corresponds to the fraction of water molecules involved in a regular tetrahedral network, as a function of the temperature for the 20 wt.% C10E3–water system. The dashed lines represent the approximate borders of the phases (Lα, lamellar phase; L3, sponge phase) as estimated by the observation with phase contrast microscopy.Figure optionsDownload high-quality image (55 K)Download as PowerPoint slideHighlights
► The water structure confined in lyotropic membrane phases differs from bulk water.
► Confinement effects disrupt the regular hydrogen bonding water structure in both phases.
► The OH stretching band can be used as a probe to follow lyotropic phase transitions.
► The regular tetrahedral water structure is strongly perturbed in the sponge phase.