Kamysbayev Vladislav, Srivastava Vishwas, Ludwig Nicholas B, Borkiewicz Olaf J, Zhang Hao, Ilavsky Jan, Lee Byeongdu, Chapman Karena W, Vaikuntanathan Suriyanarayanan, Talapin Dmitri V
Department of Chemistry and James Franck Institute , University of Chicago , Chicago , Illinois 60637 , United States.
X-ray Science Division, Advanced Photon Source , Argonne National Laboratory , Argonne , Illinois 60439 , United States.
ACS Nano. 2019 May 28;13(5):5760-5770. doi: 10.1021/acsnano.9b01292. Epub 2019 Apr 16.
The nature of the interface between the solute and the solvent in a colloidal solution has attracted attention for a long time. For example, the surface of colloidal nanocrystals (NCs) is specially designed to impart colloidal stability in a variety of polar and nonpolar solvents. This work focuses on a special type of colloids where the solvent is a molten inorganic salt or organic ionic liquid. The stability of such colloids is hard to rationalize because solvents with high density of mobile charges efficiently screen the electrostatic double-layer repulsion, and purely ionic molten salts represent an extreme case where the Debye length is only ∼1 Å. We present a detailed investigation of NC dispersions in molten salts and ionic liquids using small-angle X-ray scattering (SAXS), atomic pair distribution function (PDF) analysis and molecular dynamics (MD) simulations. Our SAXS analysis confirms that a wide variety of NCs (Pt, CdSe/CdS, InP, InAs, ZrO) can be uniformly dispersed in molten salts like AlCl/NaCl/KCl (AlCl/AlCl) and NaSCN/KSCN and in ionic liquids like 1-butyl-3-methylimidazolium halides (BMIMX, where X = Cl, Br, I). By using a combination of PDF analysis and molecular modeling, we demonstrate that the NC surface induces a solvent restructuring with electrostatic correlations extending an order of magnitude beyond the Debye screening length. These strong oscillatory ion-ion correlations, which are not accounted by the traditional mechanisms of steric and electrostatic stabilization of colloids, offer additional insight into solvent-solute interactions and enable apparently "impossible" colloidal stabilization in highly ionized media.
胶体溶液中溶质与溶剂之间界面的性质长期以来一直备受关注。例如，胶体纳米晶体（NCs）的表面经过特殊设计，以在各种极性和非极性溶剂中赋予胶体稳定性。这项工作聚焦于一种特殊类型的胶体，其中溶剂是熔融无机盐或有机离子液体。此类胶体的稳定性难以合理解释，因为具有高密度移动电荷的溶剂能有效屏蔽静电双层排斥力，而纯离子熔融盐代表了一种极端情况，其德拜长度仅约为1 Å。我们使用小角X射线散射（SAXS）、原子对分布函数（PDF）分析和分子动力学（MD）模拟，对NCs在熔融盐和离子液体中的分散情况进行了详细研究。我们的SAXS分析证实，多种NCs（Pt、CdSe/CdS、InP、InAs、ZrO）可以均匀分散在AlCl/NaCl/KCl（AlCl/AlCl）和NaSCN/KSCN等熔融盐以及1-丁基-3-甲基咪唑鎓卤化物（BMIMX，其中X = Cl、Br、I）等离子液体中。通过结合PDF分析和分子建模，我们证明NC表面会引发溶剂重构，其静电相关性延伸至德拜屏蔽长度之外一个数量级。这些强烈的振荡离子-离子相关性，传统的胶体空间位阻和静电稳定机制无法解释，为溶剂-溶质相互作用提供了额外的见解，并使得在高度电离介质中实现看似“不可能”的胶体稳定成为可能。
