Processing–Structure Relationships in Epoxy Nanocomposites Filled with GNP, GO, and MoS2: Contact-Sensitive Impedance and Raman Mapping

This study examines how filler-specific processing and the resulting spatial organization govern the structural response and measured electrical behaviour of epoxy nanocomposites containing graphene nanoplatelets (GNP), graphene oxide (GO), or molybdenum disulfide (MoS2). Bulk specimens and spin-coated films containing 0.25–5 wt% nominal filler were prepared with 22 wt% and 8 wt% A1 amine hardener, respectively. GNP and MoS2 formulations required pulsed sonication followed by planetary mixing, whereas GO was processed by planetary mixing alone; temporary isopropanol was additionally required for the nominal 5 wt% GNP formulation. Film thickness, low-frequency impedance, diamond-ATR FTIR spectra, Raman spectra, and planar and cross-sectional Raman maps were evaluated. Films from the higher nominal GNP-loading formulation showed the clearest increase in mean thickness, consistent with concentration-dependent rheology and platelet interactions during spin coating. The impedance response was strongly contact-sensitive. Under identical embedded-contact conditions, the specimen prepared from the nominal 5 wt% GNP formulation exhibited substantially lower impedance than neat epoxy across the common frequency range, with a median |Z_GNP|/|Z_epoxy| ratio of approximately 0.16. The persistence of this difference across the common frequency interval provides a clear same-fixture electrical distinction between the two tested specimens. Because one specimen was examined per condition, this result is reported at the specimen level and is not used to assign bulk conductivity, a unique conduction mechanism, or a numerical percolation threshold. ATR-FTIR showed preservation of the epoxy fingerprint together with the oxygen-rich GO contribution, while Raman spectroscopy retained the characteristic carbon and MoS2 signatures. Raman mapping showed isolated filler-rich domains at nominal 0.25 wt% and broader, more spatially continuous domains at nominal 5 wt% for the matched GNP and GO datasets, while cross-sectional mapping confirmed subsurface filler signatures for all three systems. Together, the results establish a processing–structure–measurement framework for these three 2D-filler/epoxy systems and identify the experimental controls needed for reliable interpretation of functional response.