NMR Self-Diffusion and Transverse Relaxation Time in Bitumen: The Effect of Aging

In this investigation the dynamics of two types of bitumens with different penetration grade were tested by using dynamic shear rheometry (DSR) and Nuclear Magnetic Resonance (NMR) at unaged conditions, and upon both short-and long-term artificial aging. The gel-sol transition temperature T*(gel!sol) was found to increase with increasing the time of aging treatment. Arrhenius parameters of the viscosity were found, unexpectedly, to be correlated with those of simple liquids, suggesting that the two kinds of systems, although chemically and physically quite different, share the same basic process at the molecular level. The molecular dynamics has been then investigated by NMR Pulsed Field Gradient Stimulated-Echo (PFGSE) and relaxometry (Carr-Purcell-Meiboom-Gill, CPMG, spin-echo pulse sequence) to capture the effect of aging upon dynamics variables such as self-diffusion coefficients D and transverse relaxation times T-2. The translational diffusion at T> T*(gel!sol) of the light molecular components of both types of bitumens was characterized by broad distributions of D which were found independent of the experimental time scale up to 0.2 s. Similarly, T2 data could be described as a continuous unimodal distributions of relaxation times determined both at T< T*(gel!sol) and T> T*(gel!sol).

Automated summary

In this investigation, the dynamics of two types of bitumens with different penetration grade were tested under unaged conditions and upon short- and long-term artificial aging using DSR and NMR. The study found that the gel-sol transition temperature increased with aging time, and unexpectedly, the viscosity parameters were correlated with those of simple liquids, indicating a shared basic process at the molecular level. NMR techniques were used to investigate the molecular dynamics, including self-diffusion coefficients and relaxation times, and it was found that the translational diffusion and relaxation times showed broad distributions and continuous unimodal distributions, respectively.