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首页> 外文期刊>The journal of physical chemistry, C. Nanomaterials and interfaces >Underlying Molecular Interactions between Sodium Montmorillonite Clay and Acidic Bitumen
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Underlying Molecular Interactions between Sodium Montmorillonite Clay and Acidic Bitumen

机译：蒙脱石粘土和酸性沥青之间的潜在分子相互作用

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摘要

Moisture damage is one of the common distresses in pavements; it is mainly associated with failure of interfacial bonds between bitumen and the stone aggregates that form the skeleton of pavement. The presence of acid compounds at the interface of bitumen and stone aggregates, especially siliceous aggregates, is implicated as a potential cause of interfacial failure, especially in the presence of moisture. This study investigates the merits of doping bitumen with sodium montmorillonite clay (MMT) as a sink for acid molecules, preventing them from reaching the interface of bitumen and stone aggregates. In a case study performed on bitumen doped with hexadecanoic acid, atomic force microscopy images clearly showed excessive growth of acid microstructures around the MMT particles, accompanied by a notable reduction of acid crystallization at the interface of bitumen and stone aggregates, indicating that MMT filler could be used to adsorb alkyl acid compounds. The high adsorption capacity of sodium montmorillonite clay was studied through quantum-based density functional theory (DFT) calculations. Based on the DFT results, three adsorption sites were identified for the mineral clay: hydroxyl groups protruding from the broken edges of clay, siloxane sites of the basal surface, and exchangeable cations in interlayer space. The adsorption on to edge surfaces is well stabilized by an extensive H-bonding network in this domain via the silanol groups (Si-OH). The dipole-dipole interactions between an acid and a siloxane surface carrying a negative charge make siloxane an active site for trapping acid molecules from bitumen binder. The interaction of acid molecules with the surface through Na+ cations was associated with a considerable adsorption energy, mostly due to the ion-dipole interactions between the oxygen of a carbonyl group (C=O) and an interlayer cation (Na+). Self-assembly of the acid molecules induced by H-bonding interactions between the head groups and van der Waals interactions between the tail alkyl groups reinforces the adsorption to form mono- or polylayers of the organic compound on the mineral surface. In agreement with recent findings, our DFT calculations corroborate the capability of saturated fatty acid to intercalate Na-montmorillonite clay sheets. This shows that acid molecules are adsorbed between adjacent clay layers, highlighting the role of clay as a highly efficient sorbent for saturated organic acids. The study results provide insights about the mechanisms by which clay minerals adsorb acids and prevent their migration to the bitumen-aggregate interface, consequently enhancing interfacial strength against moisture damage.
机译：水分损坏是人行道中的常见痛苦之一;它主要与沥青之间的界面键失败和形成路面骨架之间的界面键失败有关。在沥青和石聚集体的界面处存在酸化合物，尤其是硅质聚集体，涉及界面失效的潜在原因，特别是在存在水分的情况下。本研究研究了用蒙脱石粘土（MMT）的掺杂沥青作为酸分子的水槽的优点，防止它们达到沥青和石骨料的界面。在对掺杂六烷酸掺杂的沥青的情况下，原子力显微镜图像清楚地显示酸微粒周围的酸微观结构的过度生长，伴随着沥青和石骨料界面处的酸结晶的显着降低，表明MMT填充物可以用于吸附烷基酸化合物。通过量子的密度泛函理论（DFT）计算研究了蒙脱石粘土的高吸附能力。基于DFT结果，鉴定了三种吸附位点，用于矿物粘土：从粘土的破碎边缘突出的羟基，在层间空间中的可更换阳离子。通过该结构域通过硅烷醇基团（Si-OH）在该结构域中的广泛的H键合网络稳定，对边缘表面的吸附很好。酸和硅氧烷表面之间的偶极偶极相互作用使负电荷制成硅氧烷是从沥青粘合剂捕获酸分子的活性位点。酸分子与表面通过Na +阳离子的相互作用与具有相当大的吸附能相关，主要是由于羰基（C = O）的氧与层间阳离子（Na +）之间的离子偶极相互作用。通过H键合相互作用在尾烷基之间的H键合相互作用诱导的酸分子的自组装增强了吸附以在矿物表面上形成有机化合物的单或聚物。同意最近的发现，我们的DFT计算证实了饱和脂肪酸的能力，以嵌入Na-Montmorillililonite粘土片材。这表明酸分子被吸附在相邻的粘土层之间，突出粘土作为饱和有机酸的高效吸附剂的作用。研究结果提供了关于粘土矿物吸附酸的机制的见解，并防止其迁移到沥青聚集界面，因此提高了抗水分损伤的界面强度。

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