The role of hydrogen-bonded interphase in achieving optimal performance of nitrile-butadiene rubber/graphene oxide nanocomposites

Graphene oxide (GO) nanosheets (0.5-2.0 phr) were incorporated into nitrile-butadiene rubber (NBR) to clarify how interfacial chemistry and dispersion control macroscopic performance. GO was synthesized by a modified Hummers method, and different filler concentrations of NBR/GO were prepared via solution-coagulation followed by sulfur vulcanization. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) confirmed multilayer GO and best sheet dispersion at 1 phr, whereas 2 phr showed initial aggregation. Fourier-transform infrared spectroscopy (FTIR) confirmed that the NBR backbone and nitrile groups remained intact, while weak GO-derived C-O-C/C-O bands appeared at higher loadings. The C≡N band at ∼2,237 cm^-1 preserved its position but showed a slight increase in bandwidth, consistent with the formation of a hydrogen-bonded interphase. X-ray diffraction (XRD) showed loss of GO periodicity in the rubber matrix. UV-Vis/Tauc analysis indicated a non-monotonic band gap (direct 3.01→3.13→3.11 eV; indirect 2.84→2.92→2.96 eV), arising from confinement at well-dispersed loadings and π-π stacking at higher loadings. Dielectric measurements (10²-10⁶ Hz, 20 °C-100 °C) evidenced a more stable ε' for GO-filled samples, maximized at 1 phr. Mechanical testing showed simultaneous gains in tensile strength, tear resistance, and rebound elasticity at low GO loadings, while swelling and thermo-oxidative retention improved due to barrier effects and chain immobilization. Overall, ∼1 phr GO delivers the best structure-property balance, combining hydrogen-bond-mediated interfacial adhesion and optimal dispersion with stable dielectric behavior and reduced swelling/aging sensitivity; 2 phr yields the highest tensile value but also results in incipient aggregation and reduced dielectric stability.