Imaging and Spectroscopic Analysis of Bitumen

Atomic force microscopy (AFM) is capable to picture the topology of bitumen at a submicrometer level and optical spectroscopy can gather chemical information [1-3]. Here we combine AFM and Raman spectroscopy, which allows a better specification of the chemical origin of bitumen. AFM imaging was performed from the topology, following with Raman imaging from the same area correlating the chemical composition of bitumen with each point of the image. The major challenge in applying Raman is the highly fluorescent character of bitumen, which interferes with Raman and in worst case pyrolysis products are built due to laser absorption at high laser power. Here, this problem has successfully been solved through surface enhanced Raman spectroscopy (SERS) applying silver nanoparticles on the bitumen surface. This application also enables Raman spectroscopy with low laser power, i.e. 0,5 mW at 532 nm. In contrast to former research [4], where Raman spectra were obtained from carbonized bitumen, in this case SERS spectra from virgin bitumen were recorded for the first time. Previous publications [4] only presented carbonized bitumen, which is not suited to draw conclusions regarding the chemical composition of the original bitumen. In the past, several methods for unravelling bitumen microstructure were developed and applied. However, the here presented method will allow additional clues concerning the mechanical properties and the aging behavior of bitumen at a macroscopic level. The high lateral resolution of the new approach is also a step closer to the chemical origin of the structure of the core-shell particles which are situated on the bitumen sample surface.