Terahertz nondestructive evaluation of Ta4C3TX/polyacrylamide hydrogels: Microstructure characterization and structure-property correlations

This study successfully synthesized MXene/polyacrylamide (Ta 4 C 3 T X /PAM) composite hydrogels via in situ polymerization and systematically investigated their terahertz response and electrical properties. Reflective terahertz time-domain spectroscopy (THz-TDS) was employed to characterize the composite microstructure, with a focus on evaluating MXene nanosheet dispersion and mapping the surface morphology. This approach enabled the clear visualization of both internal conductive networks and surface structural features, providing critical insights into conductive network formation and surface uniformity. A Kramers–Kronig-based phase correction method was implemented to accurately extract optical constants, while a novel compressed-sensing algorithm significantly enhanced the reconstruction quality of terahertz images. The key findings demonstrate that MXene incorporation enhances terahertz reflectivity, absorption, and electrical conductivity, with distinct resonance peaks observed across the terahertz band. Spatial analysis of terahertz parameters further enabled mapping of MXene distribution and assessment of network connectivity. In particular, directional statistical analysis of the reconstructed images was performed to derive alternating-current (AC) conductivity along different orientations, revealing significant anisotropic charge transport behavior in the composite. This work establishes terahertz waves as an effective tool for analyzing internal conductive networks and surface morphology in composite hydrogels, correlating microstructural features—such as filler dispersion, network connectivity, and surface topography—with macroscopic functional properties. A proposed multilevel interaction mechanism elucidates the synergistic roles of impedance matching, scattering, and energy dissipation in the enhanced terahertz response. These findings underscore the strong potential of terahertz technology as an advanced non‑destructive testing method for the structural and functional evaluation of functional composite materials.