Fused Aromatics To Restore Molecular Packing of Aged Bituminous Materials
F Pahlavan and S Hosseinnezhad and A Samieadel and A Hung and E Fini, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 58, 11939-11953 (2019).
This study incorporates computational and laboratory experiments to determine specific interaction mechanisms between conjugated structures (interrupted and continuous conjugates) and selected polyaromatics hydrocarbons (PAH) stacks such as those found in oxidized asphaltene molecules. The theoretical results obtained by quantum-mechanical calculations and molecular dynamics simulations show that both continuous and interrupted conjugates are effective to weaken the pi- intersheet forces and decrease the size of PAH nanoaggregates, with interrupted conjugates being more efficient than continuous conjugates to exfoliate PAH stacks. Owing to their limited partial entrance into the PAH stacks, interrupted conjugates are not trapped inside the PAR interlayer, and can easily detach from the stacks. This allows an interrupted conjugate not to be consumed in interaction with one PAH stack, making the interrupted conjugate available to affect many other stacks in the matrix. The higher exfoliation capacity of the interrupted aromatic conjugates is also evidenced in the results of our experiments based on UV-vis and rheometry analyses. This is reflected in a higher reduction in the polydispersity index and a higher increase in both the crossover frequency and crossover modulus of aged bitumen (containing stacks of large PAH referred to as asphaltene nanoaggregates) when it is doped with an interrupted conjugate (fluoranthene) compared to when it is doped with a continuous conjugate (pyrene). The study results contribute to the body of knowledge by providing an in-depth understanding of how variation in the pi-electron distribution of conjugated structures affects their efficacy to exfoliated self- assembled stacked structures of polyaromatic hydrocarbons such as asphaltenes.
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