The influence of polar additives on chromonic mesophase formation of Edicol Sunset Yellow

Partial phase diagrams have been determined for the chromonic mesogen Edicol Sunset Yellow (ESY) in the presence of urea and formamide. Both additives reduce the composition ranges of the nematic and hexagonal phases compared to water alone, but the effects are quite small. Up to 10 m urea reduces the mesophase regions by ca 40°C. NMR measurements of 2H quadrupole splitting show that the interaction of urea with the ESY aggregates cannot be explained by the same simple ‘bound/free’ two-state model that fits the water binding. The addition of urea does not displace bound water, for example by competition with water for H-bonding sites. For the urea, there appears to be a larger fraction associated with the stacks on increasing ESY concentration. We suggest that this is due to urea molecules being ‘forced’ to occupy sites between the ESY within the stacks because of the restricted solvent regions (ca 1 nm), resulting in mesophase destabilisation.