Challenges While Performing AFM on Bitumen

Using modern microscopic techniques such as atomic force microscopy (AFM) has added significant knowledge on the microstructure of bitumen. The advantages of AFM are that it requires relatively simple sample preparation and operates under ambient conditions. As the use of AFM is becoming more widespread and useful the RILEM technical committee (TC) on nano bituminous materials NBM 231 has conducted a round robin study on this method, the results with respect to reproducibility, repeatability or accuracy limits are presented elsewhere. However, the execution of good quality AFM experiments especially on bitumen is still a challenging task. Sample extraction and preparation are very crucial and attention should be paid to obtain homogenous samples with a sufficient thickness and no surface contamination. The preparation should include a high temperature treatment to provide a smooth homogenous surface. Annealing/resting of the sample has to be sufficiently long, at least 24 h under ambient temperatures to ensure the formation of a (meta)stable micro-structure. Imaging should be done using non-contact (Tapping) mode with stiff cantilevers (resonance frequency ~300 kHz) with a minimum amount of damping as possible.