A Defective Lamellar Phase in a Nonionic Surfactant Water System Studied by NMR Methods

Abstract

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(C 12 E 5 )/decane/water system has been studied by 1 H-NMR pulsed field gradient experiments (PGSE) and 2 H-NMR line shapes of D 2 O, 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 S+O weight fraction from 5 to 82 wt%, three types of bilayer organisation have been found. At low surfactant+oil concentrations, <45wt% S+O, 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 presence of three-dimensional water diffusion. At concentration higher than 68 wt% S+O this defected lamellar phase oriented in the magnetic field, giving a mono-domain structure.