Disconnected lamellar phases (Lα)(Lα) in pseudobinary water–non-ionic surfactant systems: A general phenomenon

This study provides new experimental evidence for the disconnection of the lamellar phase (Lα)(Lα) in pseudobinary water–non-ionic surfactant systems. To prove that the disconnection is indeed a general phenomenon the phase behavior of the pseudobinary system water–pentaethylene glycol dodecyl ether/hexaethylene glycol dodecyl ether (H2O–C12E5/C12E6) was investigated as a function of the surfactant composition δ and the total surfactant concentration γ. At a fixed γ of 0.10 the extension of the highly diluted Lα phase shrank continuously with increasing amount of C12E6, i.e., increasing δ  , until it disappeared at δ=0.60δ=0.60. The γ–T phase diagram of this particular surfactant mixture was found to have a disconnected Lα phase. For the first time, SAXS measurements were carried out to monitor structural changes related to the disconnection. For this purpose the interlayer spacing d   and the effective cross-sectional area asas were determined from the SAXS data along characteristic paths through the Lα phase.

Schematic drawing of a phase diagram, in which a disconnected Lα phase is formed. Undulating bilayers of the dilute Lα phase (left) and stacked monolayers of the concentrated Lα phase (right).Figure optionsDownload as PowerPoint slide