The composites of graphene oxide (GO) with epoxy resin were prepared via the homogeneous liquid phase transfer method, allowing uniform distribution and nearly fully exfoliated condition of GO in the matrix. The ∼0.6% GO content is the absolute maximum that can be inserted into the epoxy matrix (at the flakes’ size 5–20 μm) without sacrificing the exfoliation level of the 2D filler and the uniformity of the composition. Curing at 180 °C causes the in situ disproportionation, or so-called “thermal reduction” of GO in the matrix. The as-induced conductivity of GO flakes alters dielectric properties of composites via the Maxwell–Wagner polarization. For the first time, we experimentally demonstrate the dielectric properties of composite materials comprising truly 2D single-atomic-layer structures. They exhibit relatively low permittivity values that reach saturation at ∼0.2% filling fraction, and classical relaxation peaks on the imaginary part function at 0.3–0.4% GO content. The presented experimental data strongly suggest that the Maxwell–Wagner polarization is sufficiently suppressed in composites comprising truly 2D structures because of their interaction with the matrix. On the contrary, high permittivity values, reported simultaneously with the high loading fractions (>0.6% at the flakes’ size 5–20 μm), are indicative of the nonsingle-layer character and/or the aggregation of the 2D inclusion particles in the polymer matrix.

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In this study, we report the properties of the epoxy polymer composites, comprising reduced graphene oxide (RGO) in the form of the single-atomic-layer sheets. This structure is different from composites comprising multilayer RGO flakes and RGO aggregates, typically described in the literature. Viscosity of the uncured liquid resin increases by 390% after introducing 0.4% GO and increases by 4700% after its subsequent in situ reduction. The latter is explained by the reorganization of the original liquid crystalline structure of the GO-epoxy formulations with GO reduction. At the filling fractions >0.1%, the single-atomic-layer RGO flakes are assembled into clusters, where they alternate with a thin resin layer. This structure is also responsible for very unusual dielectric behavior of the cured solid composites. From one side, the real part of the complex permittivity reaches relatively high values at extremely low filling fractions: 14 at 0.1% and 60 at 0.4% RGO content. At the same time, the permittivity dispersion is accompanied with the well-pronounced symmetrical loss peaks on the imaginary part functions, which is typical for low permittivity materials. Such dielectric behavior is difficult to interpret in the frames of any single existing model. The high permittivity values strongly evidence for the Maxwell-Wagner interfacial polarization, even though the shape of the loss peaks would be better interpreted by αand/or β-relaxation in neat solid polymers. The single-atomiclayer character of RGO affords a high interfacial area, which, in turn, translates to high capacitance and high permittivity. The relaxation time and activation energy, calculated from the temperature dependence experiments, suggest that the RGO clusters, but not individual RGO flakes, serve as conductive inclusions. The extremely long relaxation times are due to the charge transfer between the individual RGO flakes within the clusters. The striking difference between the newly prepared composites and control samples comprising multilayer RGO particles exemplifies the unique structure of our materials.