Solvent isotopic effect on the phase transition of lyotropic chromonic liquid crystals: Heavy water makes mesogens less charged

Jiyong Cheon; Joonwoo Jeong

paper

Solvent isotopic effect on the phase transition of lyotropic chromonic liquid crystals: Heavy water makes mesogens less charged

arXiv:2409.05097

Abstract

The interplay among solute and solvent molecules in lyotropic mesophases governs their physicochemical properties, such as phase behaviors and viscoelasticity. In our model system, a lyotropic chromonic liquid crystal (LCLC) made by disodium cromoglycate (DSCG), charged plank-like molecules self-assemble to form elongated aggregates via non-covalent attractions in water (H $_{2}$ O). The aggregates align to exhibit liquid crystalline phases: nematic and columnar phases. Here, we report the isotopic effect on the phase behavior of the LCLC when D $_{2}$ O is substituted for H $_{2}$ O. D $_{2}$ O-DSCG exhibits higher nematic-to-isotropic phase transition temperatures than H $_{2}$ O-DSCG. X-ray scattering reveals considerably longer inter-aggregate correlation lengths in D $_{2}$ O-LCLCs. In contrast, the other microstructural properties, such as inter-aggregate distances and intra-aggregate correlation lengths, remain almost the same. Our $^{23}$ Na FT-NMR measurement reveals that D $_{2}$ O-DSCG aggregates are less charged with more counter-ions, Na $^{+}$ , bound to them than H $_{2}$ O-DSCG aggregates. Weaker electrostatic repulsion between aggregates may stabilize the nematic phase, and this solvent isotopic effect may generally apply to diverse aqueous lyotropic mesophases with electrostatic interactions.