Quantifying Interphase Evolution in Epoxy/WS2 Nanocomposites: A Raman Spectroscopic Study of Aminoacetic Acid Surface Modification

The performance of polymer nanocomposites is governed primarily by the structure and properties of the matrix–filler interphase. This study presents a quantitative Raman spectroscopy analysis of interphase evolution in epoxy nanocomposites reinforced with two-dimensional WS2, whose surface chemistry was systematically tuned via grafting of aminoacetic acid (AA) at concentrations of 2.5, 5.0, and 7.5 wt.%. By tracking peak shifts, linewidths, intensity ratios, and integrated areas of the characteristic WS2 phonon modes (2LA(M) + E2g1, A1g, and defect-related bands), we establish a non-linear, concentration-dependent interfacial response. Minor spectral variations at 2.5 wt.% AA indicate limited interfacial interaction. At 5.0 wt.% AA, suppression of the A1g mode and significant band broadening reflect increased structural disorder. At 7.5 wt.% AA, coordinated red shifts (~−1.8 cm−1) and the appearance of an additional band near 432.8 cm−1 suggest the development of a strain-mediated interfacial state. Overall, increasing AA concentration leads to a non-linear evolution of the WS2–epoxy interface, as reflected in peak positions, linewidths and intensity ratios. These Raman-derived descriptors correlate directly with enhanced mechanical properties (flexural and tensile strength) and thermal stability (Vicat softening point) of the composites. The results demonstrate that effective interfacial coupling requires a critical surface coverage and that Raman spectroscopy serves as a powerful tool for non-destructively probing and optimizing interphase architecture in TMD/polymer systems.