Investigation of the creep and glass transition of elastomers by the microindentation method: Epoxy resin and related nanocomposites

The experimental procedure and theoretical grounds of the applicability of the microindentation method as one of the effective techniques of relaxation spectrometry of solid-state polymers have been developed. It has been shown that the glass transition temperature and rheological parameters of the material (unrelaxed and relaxed elastic moduli, strain viscosity coefficients) can be determined from measurements of the temperature dependence of the microhardness of polymers in a high-elasticity state and in the glass transition region with the recording of the long-term creep under the indenter. These measurements provide sufficient information for the formulation of a rheological model of the material under investigation. The results of these measurements are supplemented by the concepts of thermally activated motion of molecular segments as the microscopic mechanism of structural relaxation in polymers, which makes it possible to obtain empirical estimates for the activation energies and vibrational frequencies of the molecular segments. The method is implemented in experiments on the microindentation of the epoxy resin and its composites with the addition of carbon nanotubes in the temperature range 230–300 K. The glass transition of these polymers has been observed at temperatures near 260 K, the unrelaxed and relaxed Young’s moduli have been measured, and two thermally activated relaxation processes determining the glass transition, as well as the shortterm and long-term creeps of these materials ($\alpha$- and $\alpha'$-processes), have been revealed.