Molecular dynamics simulation and microscopic observation of compatibility and interphase of composited polymer modified asphalt with carbon nanotubes

Abstract

Interfacing and compatibility are the most challenging issues that affect the performance of polymer modified asphalt. Mechanisms of interfacial enhancement among four base asphalt components (asphaltenes, resins, aromatics, and saturate), styrene-butadiene-styrene (SBS), and carbon nanotubes (CNTs) were investigated by molecular dynamics simulation, with the aim of understanding the key parameters that control the compatibility of CNTs and interphase behavior on the molecular scale. The compatibility of SBS-modified asphalt (SBSMA) was simulated based on self-assembly theory using indexes of binding energy, mean square displacement, diffusion coefficient, and relative concentration distribution. The interphase behavior and microstructure were observed by fluorescence microscopy and scanning electron microscopy. In addition, a rutting experiment was used to verify the molecular dynamics simulation based on macroscopic performance. The results showed that after adding CNTs, the binding energy of the SBS and aromatics increased from 301.8343 to 327.1102 kcal/mol. The diffusion coefficient of the SBS and asphaltenes decreased more than 3.2×10⁻¹¹ m²/s, and the correlation coefficients between the diffusion coefficient and the molecular weight, surface area and volume were all lower than 0.3. Relative concentration distribution curves indicated that CNTs promote the ability of SBS to swell. Microscopic observations demonstrated that the swelling ability of SBS was increased by CNTs. Overall, the interphase of SBSMA was improved by the additional reinforcement, swelling, and diffusion provided by CNTs. Finally, the rutting experiment found that no matter what the temperature, the rutting factor of CNT/SBSMA is higher than that of SBSMA, which corroborates the findings from the molecular dynamics simulations.

概要

目的

利用碳纳米管(CNT)增强苯乙烯-丁二烯-苯乙烯(SBS)改性沥青的相容性,并利用分子动力学模拟探索其微观机制。

创新点

利用分子动力学模拟从分子尺度解释了CNT对SBS改性沥青相容性的增强机制,并解释了荧光显微镜、扫描电镜和车辙因子实验的结果。

方法

本文采用分子动力学模拟、微观形貌观察和动态力学分析等方法进行研究。

结论

1. SBS将与沥青质竞争沥青系统中的轻质成分,这会导致SBS膨胀不足;2. CNT的加入大大增加了沥青中各种分子与SBS聚合物的结合能,使SBS改性的沥青体系更加稳定;3. 通过对两种改性沥青体系的结合能进行T检验,发现CNT并没有影响SBS和沥青之间的弱相互作用;4. 沥青分子的运动主要取决于体系中分子间的相互作用,而不是分子表面积、分子量和体积;5. CNT的加入使得芳香分和饱和分的分布更加均匀,缓解了SBS和沥青质之间的竞争,促进了SBS的膨胀;6. 荧光显微镜、扫描电镜和车辙实验的结果验证了分子模拟的结论。