Modulus mapping of rubbers using micro- and nano-indentation techniques

Modulus measurements are among the most useful properties available for monitoring the cure and aging of rubbers. Historically, such measurements were done on macroscopic samples, but over the past 15 years, several penetration techniques have been and are being developed that allow quantitative estimates of modulus to be made with lateral resolutions of 100 mum or better. This review summarizes these developments and the types of unique information that can be generated on rubbery materials. A large part of the review focuses on the types of results available from a modulus profiling apparatus that has been used to study rubbers for the past 15 years. This instrument allows estimates to be made of the inverse tensile compliance (closely related to Young's tensile modulus) with a lateral resolution of around 50 to 100 mum. Several recently developed alternative methods for achieving similar spatial resolution are also described. Finally, a brief review is given of the recent attempts to measure quantitative modulus values for rubbers with even better resolution using instruments historically focused on metals and other hard materials such as nano-indenters, the atomic force microscope and the interfacial force microscope.