A hybrid model to determine mechanical properties of soft polymers by nanoindentation

In nanoindentation tests for soft polymers, the elastic modulus estimated from the Hertz model varies with applied force, implying the effect of adhesion work needs to be considered in contact theory. In this article, a hybrid method of combining the Hertz model and the Johnson–Kendall–Roberts (JKR) model is presented, to analytically explain the descending phenomenon of the modulus estimation by considering adhesive effects. Thus both the force-independent elastic modulus and the adhesion work can be evaluated by fitting the experimental data, without need to know the adhesive force in advance. The successful application to the measurement of polydimethylsiloxane (PDMS) material’s elastic modulus demonstrates the method is applicable to the mechanical characterization of soft polymers by nanoindentation.