Aggregation of model asphaltenes: effect of chain length and functional groups

The relationship between the chemical structures of natural asphaltenes and their aggregation mechanism remains poorly understood. To establish the influence of different chemical functional groups on the aggregation pathway of natural asphaltenes, a series of model triphenylene-based compounds were investigated. Synthesized with alkoxy chains of varying length and amide appendages, both with and without an acid terminating moiety, their aggregation kinetics in toluene were studied over several length scales, using a combination of dynamic light scattering (DLS) and diffusion-ordered NMR spectroscopy, complemented with GROMACS molecular dynamics (MD) simulations. The chemical structures of the polyaromatic compounds play an important role in their aggregation behavior: non-centrosymmetric model compounds were more prone to aggregation and formed large clusters. Furthermore, polar components appear to have a more significant influence than π-stacking on the driving force of aggregation, as the large clusters formed were observed to possess multiple configurations. Both amide and acid groups could generate strong attractive forces between molecules, overcoming the energy barrier imposed by the aromatic solvent and molecular core. These conclusions underline a strong structure-function relationship, of a model system examined on multiple size-scales, in a single solvent.

天然沥青的化学结构与它们的聚集机制之间的关系尚缺乏深入理解。为了确立不同化学官能团对天然沥青聚集途径的影响，一系列以三苯基为基础的模型化合物被研究。这些化合物通过不同长度的烷氧基链和酰胺基团合成，包括有无羧酸终止基团的情况。在甲苯中，它们的聚集动力学被研究，跨越了多个长度尺度，采用动态光散射（DLS）和扩散有序核磁共振波谱（NMR）相结合的方法，并辅以GROMACS分子动力学（MD）模拟。多芳烃化合物的化学结构在其聚集行为中起着至关重要的作用：非中心对称的模型化合物更易聚集，并形成大型的聚集体。此外，极性组分似乎比π-堆积对聚集驱动力有更显著的影响，因为观察到形成的大聚集体具有多种构型。酰胺和羧酸基团均能产生分子间强烈的吸引力，克服由芳香族溶剂和分子核施加的能量壁垒。这些结论在一个单一溶剂中，针对多尺度模型系统的研究中，揭示了结构-功能之间强烈的关联性。