Application of atomic force microscopy in bitumen materials at the nanoscale: A review

This article reviews the state-of-the-art application of AFM in the field of bitumen materials. The working principle of conventional AFM and its derivative technologies including AFM peak force quantitative nanomechanical mode (PF-QNM) and atomic force microscopy-based infrared spectroscopy (AFM-IR) are first introduced. Then, sample preparation methods and selection methods of probes and test parameters for AFM observation are summarized to obtain high-quality bitumen maps. Following this, phase characteristics of bitumen surfaces and interiors are described, the cognition process of unique 'bee-structure' of bitumen surfaces are traced, and the similarities and differences between surface and interior phases of bitumen and the corresponding generation mechanisms are compared. Then, the application of AFM is discussed in detail. Eventually, a few technical challenges for the investigation of bitumen materials using AFM are discussed, and the corresponding potential solutions are recommended.