Chiral lyotropic chromonic liquid crystals composed of disodium cromoglycate doped with water-soluble chiral additives†
We investigated the pitches of cholesteric liquid crystals prepared by mixing disodium cromoglycate (DSCG) in water with 5 different water-soluble chiral additives. The measurements are based on the Grandjean–Cano wedge cell method. Overall, the twisting effect is weak, and the shortest pitch of 2.9 ± 0.2 μm is obtained using trans-4-hydroxy-L-proline, by which the cholesteric sample is iridescent at certain viewing angles. Freeze-fracture transmission electron microscopy (FFTEM) was also performed for the first time on both the nematic and cholesteric phases, revealing that stacked chromonic aggregates are very long, up to a few hundred nm, which explains why cholesteric chromonic liquid crystals hardly have pitches in the visible wavelength region.