The nano-/microscale stiffness and hardness of the crystalline structures developing in polyether ether ketone (PEEK), including individual spherulites and transcrystalline (TC) layers, were determined using nanoindentation and atomic force microscopy (AFM) in force spectroscopy mode in samples containing few carbon fibers. The crystalline morphologies were identified using polarized light microscopy (PLM) in transmission mode. The microstructure and weight percentage of crystallinity of each crystalline entity were also quantified using, respectively, tapping-mode (TM) AFM and Fourier transform infrared (FTIR) spectroscopy, to directly correlate the nano-/micromechanical behavior of PEEK to the crystalline structures. The crystalline structures of various dimensions involve different fraction of crystallinity as well as modulus and hardness values. The variation of the latter within individual crystalline entities can be correlated to a change of fibrils (i.e., lamellar stacks) density. These quantitative data are important in the context of optimizing the performance of PEEK based composites and of developing more predictive multiscale micromechanics-based models.
S. Vanpée, B. Nysten, A. M. Jonas, J. Chevalier, T. Pardoen, Polymer 2026, 345, 129516
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