Using the adhesive interaction between atomic force microscopy tips and polymer surfaces to measure the elastic modulus of compliant samples

An atomic force microscope (AFM) method for measuring surface elasticity based on the adhesive interactions between an AFM tip and sample surfaces is introduced. The method is particularly useful when there is a large adhesion between the tip and soft samples, when the indentation method would be less accurate. For thin and soft samples, this method will have much less interference from the substrate than is found using the indentation method because there is only passive indentation induced by tip-sample adhesion; in contrast, a large indentation with a sharp tip in the sample may break its stress-strain linearity, or even make it fracture. For the case where it is difficult to accurately locate the tip-sample contact point, which is problematic for the indentation method, the method based on adhesive interactions is helpful because it does not require locating the tip-sample contact point when fitting the whole retraction force curve. The model is tested on PDMS polymers with different degrees of cross-linking.