Surface Charge at the Bitumen/Water Interface Investigated by Phase-Sensitive Sum Frequency Generation Vibrational Spectroscopy: Effects of pH, Ions, and Surfactants

摘要

The structure of water at bitumen/water interfaces was studied using phase-sensitive sum frequency generation (SFG) vibrational spectroscopy. The sign of the SFG spectra indicated that the surface of bitumen has a negative net charge. An ordered water structure was observed on the bitumen surface, and the ordering was enhanced at the industry-relevant pH value of 9. The presence of salt in the water neutralized the surface charge of bitumen and nearly destroyed the ordered water structure with a concentration of similar to 100 mM. It was found that Ca2+ was more effective than Na+ in screening the surface charge of bitumen. Both the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant dodecyl trimethylammonium chloride (DTAC) interacted with the bitumen. While the anionic surfactant slightly increased the negative charge of the bitumen surface, the cationic surfactant produced a surface charge reversal, indicated by the sign change of the SFG spectrum.