Effects of Sodium and Magnesium Cations on the Aggregation of Chromonic Solutions Using Molecular Dynamics

Abstract

Lyotropic chromonic liquid crystals (LCLCs) constitute a unique variety of water-soluble mesogens that spontaneously assemble into elongated aggregates, thereby resulting in the formation of liquid crystal phases depending on the temperature and concentration. The influence of ionic additives on the aggregation of LCLC has been extensively studied, but the molecular mechanisms governing these effects remain unclear. In this investigation, we perform atomistic molecular dynamics simulations of dilute sunset yellow (SSY) LCLC solutions doped with NaCl and MgCl2 salts. Structural and dynamical properties of SSY hydration shells are considerably modified by the partial substitution of their H bonds with sodium/magnesium-sulfonate ion pairs. Although the intermolecular distance of ∼3.4 Å between SSY mesogens is preserved regardless of the ionic content, the growing number of ion pairs favors the reduction of the electrostatic repulsion between mesogens, increasing the length of SSY stacks. Moreover, magnesium cations exert the strongest electrostatic effects due to their higher hydration capabilities and acute electrostatic binding to SSY. For these reasons, experimental observations of dilute SSY solutions doped with Mg2+ exhibit higher nematic-to-isotropic transition temperatures than Na+. This work provides a fundamental understanding of the influence of ionic additives on the self-assembly of diluted LCLC solutions derived from the synergistic molecular mechanisms between mesogens, the solvent, and cations.

Induced Chiral Chromonics Confined in Micrometric Droplets

“…Furthermore, atomistic molecular dynamics simulations of dilute SSY LCLC solutions doped with NaCl and MgCl 2 salts show that molecules stack more efficiently by increasing the number of mesogens per stacking column, that is, raising the columnar length of individual SSY aggregates. [ 19 ] In ref. [ 17 ] the same authors demonstrate also how the simultaneous presence of Na + and L‐alanine counterions establishes a complex interconnected network of non covalent interactions which stabilizes DSCG aggregates.…”

Lyotropic Chromonic Liquid Crystals and Their Impurities Reveal the Importance of the Position of Functional Groups in Self-Assembly

“…In other words, even though we eliminate 2N-SA, SS-AN, and RS-SA by purification and replace their portions with pure SSY, i.e., to make the final concentration same, it would be hard to notice the differences in the phase transition temperatures. Therefore, we presume that 2N-SA, SS-AN, and RS-SA participate in the SSY aggregate formation, and it is because the antiparallel stacking of SSY molecules in the aggregates ,,, is not much interrupted by the changes in the peripheral groups. The subtle changes in the aggregate structures by these impurities shown in Figure c–e support this argument.…”

“…First, water-soluble chiral dopants and their helical twisting powers for chiral nematic LCLCs have been studied, extending to the study of chiral amplification under confinement. − Additionally, the effects of additives such as salts, polymers, and surfactants on the aggregates and phase behavior have been charted; ,,,− additives also affect LCLCs’ surface anchoring, wetting, and director configuration. − In short, the additives alter the inter- and intra-aggregate interactions, e.g., screening the electrostatic repulsion, changing the size distribution of the aggregates, and modifying phase boundaries and macroscopic properties. The simulations of LCLC with additives supplement these stories. , Knowing that the phases and properties of LCLCs are sensitive to the additives, it is worth noting that studies on the effects of intrinsic additives, i.e., impurities, such as raw materials, intermediates, and byproducts made during synthesis, still lack. Namely, besides the extrinsically added impurities such as chiral dopants and polymers, it is essential to investigate the effects of natural impurities.…”

Theoretical Platform for Liquid-Crystalline Self-Assembly of Collagen-Based Biomaterials

“…Simplicity of free energy expression is essential since our ultimate objective is the self-assembly simulation which in itself is computationally complex. A heavy computational load is expected because the self-assembly process covers a wide range of length scale (i.e., ranging from nano-to macro-scale) and it may go through a variety of complex microscopic mechanisms [41,[55][56][57][58][59]. Thus, to improve tractability, we expand the functional part of Equation (15), Ŵ (γ), in terms of the second Legendre polynomial by use of Equation 8:…”