A defective lamellar phase in a nonionic surfactant-water system studied by NMR methods

Lamellar phases of some surfactant water system are not infinite, continuous lamellar planes but several experimental findings showed that they contain water-filled defects with highly curved edges. Here, the polydomain lamellar phase of the pentaethylene glycol dodecyl ether(C12E5)/decane/water system has been studied by 1H-NMR pulsed field gradient experiments (PGSE) and 2H-NMR line shapes of D2O, at a constant surfactant (S) to oil (O) weight ratio of 51.8/48.2. Within the lamellar phase of this system, which was observed at SþO weight fraction from 5 to 82 wt%, three types of bilayer organisation have been found. At low surfactantþoil concentrations, <45 wt% SþO, the lamellar phase consists of a stack of flat parallel bilayers while within a intermediate- concentration regime water-filled bilayers exist, as demonstrated by the pre- sence of three-dimensional water diffusion. At concentration higher than 68 wt% SþO this defected lamellar phase oriented in the magnetic field, giving a mono-domain structure.