Nanoindentation study of polydimethylsiloxane elastic modulus using Berkovich and flat punch tips

This article explores polydimethylsiloxane (PDMS) mechanical properties, and presents nanoindentation experiments with Berkovich and flat punch indenters. In the Berkovich tip quasi-static nanoindentation test, there are pull-in and pull-off events observed during the initial tip contact, and when withdrawing from the surface, respectively. The pull-in interaction needs to be accounted for to properly determine the initial contact point, and thus the accurate contact area. Once accounted for the pull-in event, the Berkovich and flat punch tips quasi-static nanoindentation tests give comparable results of about 1.5 MPa for the PDMS elastic modulus (5 : 1 elastomer base to the curing agent ratio). However, PDMS unloading stiffness is higher than the loading stiff- ness, and dynamic PDMS testing yields higher elastic modulus of about 3.6 MPa. While these results are comparable with the large strain macroscopic compression test results, the difference underscores the complexity of elastomer mechanical characterization and illustrates the discrepancies typical of the reported values. This article describes nanoindentation methods and critical aspects of inter- preting results to assess PDMS mechanical properties. V C 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41384.