Use of scanning force microscopy studies with combined friction, stiffness and thermal diffusivity contrasts for microscopic characterization of automotive brake pads

A scanning force microscopy (SFM) study encompassing a thermal and various mechanical contrasts was performed on a sample related to automotive brake pads. The sample consisted of polybutadiene (PBD) and the solid lubricant antimony sulphide (Sb 2 S 3 ), both dispersed in a polymeric matrix of phenolic resin. Via this highly simplified composition, the assignment of contrasts to the ingredients was assured. The mechanical measurements, namely the stiffness measurements via force modulation microscopy (FMM) and the friction measurements via lateral force microscopy (LFM) and harmonically modulated lateral force microscopy (HM‐LFM), were carried out in one combined experiment (using the same silicon tip). Owing to the available stiffness data, the results of the lateral force measurements are discussed in terms of the size of the mechanical contact radius. Compared with LFM, HM‐LFM is less prone to topographic artefacts and shows enhanced contrasts. The additional phase image indicates deviations from perfect elastic behaviour. Consistently with the FMM measurement, the HM‐LFM phase image displays a distinct phase shift on PBD. For performing thermal measurements, a probe made up of Wollaston was employed. The resulting images are interpreted in terms of the thermal diffusivity and the thermal conductance of the tip– sample contact. Beyond the mechanical properties of the material under investigation, the influence of the bridging water layer also has to be taken into account.