Alteration of pi-Electron Distribution To Induce Deagglomeration in Oxidized Polar Aromatics and Asphaltenes in an Aged Asphalt Binder
F Pahlavan and AM Hung and M Zadshir and S Hosseinnezhad and EH Fini, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, 6, 6554-6569 (2018).
This paper features electronic evaluation explaining molecular association and dissociation during oxidative aging and rejuvenation process in polyaromatic hydrocarbons. Specifically, we employ both computational modeling and laboratory experiments to show how the presence of external stimuli such as biorejuvenator can alter x-electron distribution to further induce deagglomeration. To better link findings to real-world materials and application, the study is done on the oxidized asphaltene and resin molecules; in addition, the disturbance of electron distribution is done using a biorejuvenator derived from animal waste. As petroleum asphalt binder oxidizes, the association forces between polar aromatics are strengthened owing to the introduction of polar chemical functionalities to their molecular structure. This is evidenced by X-ray diffraction (XRD) measurements showing that a new peak at high d-spacing appears after oxidation that is consistent with graphene-oxide-like (GO-like) structures. The GO-like structures become amorphous after the addition of biorejuvenator (BR), and the related peak in the XRD spectra vanishes. Density functional theory calculations show a destructive effect of BR on the pi-pi interaction between polyaromatics in the aggregation. The resulting pi-electron disruption is induced by the polar head of biorejuvenator with electron-withdrawing nature and its hydrocarbon tail with the ability of CH-pi-stacking with oxidized asphalt molecule. This, in turn, indicates that the biorejuvenator can act to restore oxidized asphalt binder by disassembling asphaltene agglomerates and disrupting resinous GO-like structures through a three-stage mechanism: partial penetration into small pores around agglomerates, partial segregation of agglomerates, and finally dispersion of smaller agglomerates.
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