(661c) Chemical and Mechanical Relaxations In Multicomponent Model Bitumens

The chemical, physical, and mechanical properties of multicomponent amorphous solids represent contributions from the various molecules in the system.  A prime motivation is quantifying the mechanisms by which chemical changes invoke changes in mechanical properties, i.e. "chemo-mechanics".  As an example, this work presents  next-generation model systems for simulating asphalt/bitumen on the molecular level.  Compared to prior work (Energy Fuels 2007, 21, 1712 and 2008, 22, 3363), the molecules included are of higher molecular weight and have been observed in geochemistry studies.  Their structures, such as squalane and substituted hopanes, have biological origins.  Model asphaltene molecules proposed by others have been altered to alleviate high energies that arose from poor architecture choices. Atomistic molecular dynamics simulations are employed to predict single molecule rotation and diffusion rates. Debye-Stokes-Einstein scaling is used to relate relaxation rates to temperature-dependent mechanical properties.  Viscosity predictions show good agreement compared to representative measurements reported in the literature.  Molecules across the employed size ranges show the same diffusion activation energy, indicating common collective barriers for translation.