Intrinsic Insertion Limits of Graphene Oxide into Epoxy Resin and the Dielectric Behavior of Composites Comprising Truly 2D Structures

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.