Structure of liquid-crystalline phases formed by sodium dodecyl sulphate and water as determined by optical microscopy, X-ray diffraction and nuclear magnetic resonance spectroscopy

Abstract

The lyotropic liquid crystals formed in the sodium dodecyl sulphate + water system have been studied using optical microscopy, low-angle X-ray diffraction and nuclear magnetic resonance spectroscopy. Optical microscopy reveals the presence of a mesophase at compositions between those of the hexagonal and lamellar phases. The magnitudes of water and sodium n.m.r. quadrupole splittings indicate that this phase contains rod micelles similar to those in the hexagonal phase, despite the fact that the material aligns at glass surfaces with the director normal to the surface. The X-ray measurements suggest that the phase has a deformed hexagonal structure and results from a gradual distortion of the hexagonal lattice with increasing surfactant concentration. An hypothesis to account for its formation and properties is proposed, involving hydrogen-bonded water links between micelles.