Structure and Dynamics in Lamellar Liquid Crystals

Deuterium NMR has been used to probe the effects of mechanical agitation and aging of lamellar liquid crystals of sodium 4-(1-heptylnonyl)benzenesulfonate or sodium bis(2-ethylhexyl) sulfosuccinate with deuterium oxide. Samples prepared by vapor sorption show uniform water uptake and relatively sharp deuterium NMR powder patterns with quadrupole splittings of ca. 2 kHz. The shape of the deuterium NMR pattern was dependent upon the extent of mechanical agitation, with the limit being collapse to a single broad resonance. The NMR spectra of the mechanically agitated samples do not revert to the unagitated form over a period of years if left at room temperature. When liquid water was added directly to the dry surfactant, lamellar liquid crystals were formed which have nonuniform water content. The water becomes uniformly distributed and the deuterium NMR spectra indistinguishable from those prepared by vapor sorption only after aging for many days. The agitation-dependent line shapes can be explained by morphological changes in the liquid crystallites. © 1987 American Chemical Society