Quasi-static and dynamic compressive mechanical properties of amino acid ionic liquid-doped mixed-matrix membranes.

In this study, taking Matrimid®5218 and Pebax 1657 as polymer matrices, the amino acid ionic liquid (AAIL) [EMIm]Gln was incorporated to construct mixed-matrix membranes (MMMs), with the aim of systematically elucidating their quasi-static and dynamic mechanical responses. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) were used to characterize the functional groups, chain packing, morphology, and thermal stability of the membranes. These analyses were further integrated with nanoindentation, dynamic mechanical analysis (DMA), and uniaxial tensile testing to comprehensively evaluate local compressive behavior, viscoelastic response, and large-deformation fracture characteristics. The results demonstrate that the incorporation of [EMIm]Gln did not alter the fundamental structural framework of the membranes, but significantly enhanced segmental chain mobility. For the pristine Matrimid® membrane, the Young's modulus and hardness were 2.84 GPa and 126 MPa, respectively, which decreased to 2.21 GPa and 86 MPa after doping with 20 wt% [EMIm]Gln. In the Pebax-based MMMs, these values declined from 0.42 GPa and 28 MPa to even lower levels. DMA results further revealed that the glass transition temperature of the Matrimid®-based MMMs decreased from 310 °C to 283 °C, while the Pebax-based MMMs exhibited a continuous reduction in storage modulus accompanied by an increase in loss modulus. Overall, the introduction of [EMIm]Gln shifted the membranes from a "high-rigidity, low-energy-dissipation" regime toward a "low-rigidity, high-toughness" regime. Notably, Matrimid® was more sensitive to plasticization, whereas Pebax exhibited a stronger capacity to accommodate the ionic liquid. These findings provide a mechanistic basis for selecting suitable AAIL loadings in mechanically reliable mixed-matrix membranes.