Investigating Solvent-Induced Aggregation in Edge-Functionalized Layered Silicates via All-Atom Molecular Dynamics Simulations

Molecular dynamics simulations can provide the means to visualize and understand the role of intermolecular interactions in the mechanisms involved in molecular aggregation. Along these lines, simulations can allow the study of how surface chemical modifications can influence nanomaterial assembly at the molecular level. Layered silicate clays have been of significant interest for some time, particularly with regard to their use in organic/inorganic nanocomposites. However, despite numerous reports on the covalent linkage of organic moieties via silanol condensation, the theoretical understanding of these systems has heretofore been limited to noncovalent interactions, specifically ionic interactions at the charged basal surfaces. Herein, a model for edge-functionalized layered aluminosilicate clay, based on the siloxane linkage, is presented. In addition to reproducing experimentally observed degrees of molecular aggregation of clay-linked perylene diimide derivatives with different terminal functional groups as a function of solvent composition, a molecular-level understanding of the role of van der Waals interactions and hydrogen bonding of the different end-groups on the aggregation state in different water/N,N-dimethylformamide mixtures is obtained. The reported model provides a means to simulate organic moieties covalently bound to the layered silicate edge, which will enable future simulations of nanocomposites and organic/inorganic hybrids based on this system.分子动力学模拟（molecular dynamics simulations）可为可视化并理解分子间相互作用在分子聚集相关机制中的作用提供途径。基于此，此类模拟可用于研究表面化学修饰如何在分子层面影响纳米材料组装。长期以来，层状硅酸盐黏土（layered silicate clays）一直受到广泛关注，尤其是在其用于有机/无机纳米复合材料（organic/inorganic nanocomposites）的相关研究中。然而，尽管已有大量关于通过硅醇缩合（silanol condensation）实现有机基团（organic moieties）共价连接（covalent linkage）的报道，但目前此类体系的理论认知仍局限于非共价相互作用（noncovalent interactions），具体为带电基面（charged basal surfaces）上的离子相互作用。本文报道了一种基于硅氧键连接（siloxane linkage）的边缘功能化层状铝硅酸盐黏土（edge-functionalized layered aluminosilicate clay）模型。该模型不仅可复现实验观测到的、不同末端官能团（terminal functional groups）修饰的黏土结合苝二酰亚胺衍生物（perylene diimide derivatives）的分子聚集程度随溶剂组成（solvent composition）变化的规律，还可在分子层面揭示不同末端基团的范德华相互作用（van der Waals interactions）与氢键（hydrogen bonding）在水/N,N-二甲基甲酰胺（water/N,N-dimethylformamide）混合溶剂中对聚集状态的影响。 本研究所报道的模型可用于模拟共价结合于层状硅酸盐边缘的有机基团，将为后续基于该体系的纳米复合材料与有机/无机杂化物（organic/inorganic hybrids）的模拟研究提供支撑。