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

Jiyong Cheon; Joonwoo Jeong

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arXiv · 2409.05097

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

Jiyong Cheon·Joonwoo Jeong

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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.

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Jiyong Cheon, Joonwoo Jeong. 2024-09-08. Solvent isotopic effect on the phase transition of lyotropic chromonic liquid crystals: Heavy water makes mesogens less charged. https://arxiv.org/abs/2409.05097

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