Comparison of atomic force acoustic microscopy and dynamic nanoindentation methods for compliant polymer systems

Nanomechanical characterization of soft materials such as polymers and polymer composites represents a unique and challenging research topic of current interest. In this presentation, two characterization methods are compared directly using a set of model PDMS polymer systems. Experiments were conducted using both nanoindentation and atomic force acoustic microscopy (AFAM) to determine the dynamic mechanical properties. The experiments were conducted to determine reduced elastic modulus E* via AFAM measurement and storage modulus E via nanoindentation. The AFAM analysis was done using both a Hertzian contact model and a flat punch model. While the two methods showed marginal agreement, the resulting AFAM moduli were dependent on the model used in the analysis. Further investigation is needed to improve the accuracy of these measurements. In addition, further modeling is needed to improve the understanding of the tip-sample interaction in such systems. The results are anticipated to lead to the development of improved characterization methods for compliant materials. [Work supported by ARL.]