Effect of Free-Volume Holes on Dynamic Mechanical Properties of Epoxy Resins for Carbon-Fiber-Reinforced Polymers Studied by Positron Annihilation*

We studied the effect of free-volume holes on dynamic mechanical properties (storage modulus E', loss modulus E'', damping factor tanδ, and complex viscosity |η^*|) for six types of amine-cured epoxy resins with different chemical structures. Positron annihilation lifetime (PAL) experiments were applied to determine the free-volume hole properties of each sample. The correlations between hole fraction and dynamic mechanical parameters were studied by Williams-Landel-Ferry equation. In the temperature range of T_g(PAL)<T<T_g(PAL)+100 °C (T_g(PAL) is the T_g given by PAL experiments), regular variations of dynamic mechanical parameters with increasing relative hole fraction (1-h_PAL@Tr/h_PAL, where h_PAL is the hole fraction from PAL experiments, and h_PAL@Tr is the h_PAL at reference temperature T_r) are revealed: (1) log[E'(T)] and log[|η^*|(T)] initially decrease linearly and then remain nearly unchanged; (2) log[E''(T)] and log[tanδ(T)] initially increases linearly and then decrease linearly. In this work, PAL spectroscopy provided precious quantitative information of free-volume holes in polymers [1].

[1] H. J. Zhang, S. Sellaiyan, T. Kakizaki, A. Uedono, Y. Taniguchi, K. Hayashi, Macromolecules 50, 3933 (2017).