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arXiv 2409.05097cond-mat.soft
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溶剂同位素效应对溶致色晶液晶相变的影响:重水使介晶子电荷减少

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

Jiyong Cheon, Joonwoo Jeong

AI总结:

本研究通过相变温度、X射线散射和²³Na FT-NMR测量发现,D₂O替代H₂O会增强DSCG溶致色晶液晶的向列相稳定性,原因是更多Na⁺结合使聚集体电荷降低、静电排斥减弱。

摘要:

在溶致中间相中,溶质与溶剂分子之间的相互作用决定着它们的物理化学性质,例如相行为和黏弹性。在我们的模型体系中,由色甘酸二钠(DSCG)制成的溶致色晶液晶(LCLC)里,带电的板状分子在水(H₂O)中通过非共价吸引自组装形成细长聚集体。这些聚集体排列并呈现液晶相:向列相和柱状相。在此,我们报道了以D₂O替代H₂O时对LCLC相行为的同位素效应。D₂O-DSCG表现出比H₂O-DSCG更高的向列相-各向同性相转变温度。X射线散射显示,D₂O-LCLC中的聚集体间相关长度显著更长。相比之下,其他微结构性质,如聚集体间距离和聚集体内相关长度,几乎保持不变。我们的²³Na FT-NMR测量揭示,与H₂O-DSCG聚集体相比,D₂O-DSCG聚集体电荷更低,并有更多反离子Na⁺结合在其上。聚集体间较弱的静电排斥可能使向列相稳定,而这种溶剂同位素效应可能普遍适用于各种具有静电相互作用的水性溶致中间相。

英文摘要:

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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