EM studies of long-lived fiber gels complemented by solid state 2H-NMR spectroscopy

Abstract

Aqueous gels (1%) consisting of the amphiphilic N-octyl-D- gluconamide (D-Glu-8) usually crystallize within a few hours.They remain stable for more than five months if 0.4% of sodium dodecylsulfate (SDS) is added. It was shown by electron microscopy that the gels are formed by helical fibers of at least bimolecular thickness (4 nm) and of several micrometers length. Randomly dispersed particles with a mean diameter of 5 nm, which are assumed as micelles, were also observed on micrographs (Fig.1).To provide evidence for this assumption and to rule out the possibility of artefacts introduced by the preparative method, we applied an additional technique, namely solid state 2H-NMR spectroscopy. The spectra point out the temperature dependent equilibrium between “solid” fibers and micelles, as represented by the Pake powder spectrum and the isotropic central singlet (Fig.2). The micellar part of the equilibrium is strongly enhanced in the presence of detergents such as SDS. High concentrations of SDS micelles extend the gel’s lifetime, presumably because these micelles dissolve the crystallization nuclei of D-Glu-8 and thus, prevent further crystal growth.