N.M.R. and X-ray diffraction of the 7,7'-disodiumcromoglycate-water lyomesophases

Abstract

Aqueous solutions of 7,7'-disodiumcromoglycate (7,7'-DSCG) form a variety of mesophases, whose natures depend on concentration and temperature. We have used optical microscopy, N.M.R. (of ²H, ¹⁷O and ²³Na) and X-ray techniques to construct a phase diagram for this system and to characterize the various mesophases. In the concentration range 3 to 25 wt % 7,7'-DSCG four different mesophases are found. On cooling the isotropic solution an opaque gel phase is first obtained, followed on further cooling by a birefringent glassy liquid. At concentrations below 14wt% it is nematic, while at higher concentrations it appears to be a different, more ordered, phase. At lower temperatures a hexagonal phase is formed which finally solidifies on cooling to - 15°C. The N.M.R. and X-ray characteristics of these mesophases are discussed.