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The electromagnetic interference (EMI) shielding devices fabricated by graphene-based nanocomposites are constantly exposed to high temperature and X-band frequency during service, but at present no theory can account for such environmental effects. In this work, a micromechanics-based theory is developed to address the influence of temperature and X-band frequency on EMI shielding of graphene/silica nanocomposites. First, the temperature-dependent electromagnetic constitutive relations are established for both graphene and silica, and then the temperature-dependent electromagnetic interface effects, including electron tunneling and hopping for the conductivity and dielectric polarization and relaxation for the permittivity, are introduced. With these constituent and interface properties, the effective complex permittivity and permeability of the nanocomposite are evaluated through the effective-medium approximation. The EMI shielding effectiveness (SE) in the X-band range is calculated from Maxwell's equations under the near-field wave source. The predicted complex permittivity and EMI SE are shown to agree with the experiments of rGO/silica nanocomposites over 320–480 K and 8–12 GHz. The X-band EMI SE enhances with the increase of temperature due to the increase of reflection loss, and the temperature influence increases with the sample thickness. Several other novel attributes are also discovered. • EMI SE for graphene-based nanocomposites is studied under near-field wave source. • Temperature-dependent electromagnetic properties of graphene, matrix, and interface are included. • It is demonstrated that the EMI SE is directly connected to microstructural parameters. • The results are validated with data of rGO/silica nanocomposites over 320–480 K and 8–12 GHz. [ABSTRACT FROM AUTHOR]

While the subject of creep and recovery in polymers is not new, its temperature dependence in graphene-polymer nanocomposites is. In such nanocomposites, the interface activity plays a critical role that is absent in a pure polymer phase. Several recent experiments have also demonstrated the remarkable impact of temperature in such nanocomposites, but at present no theory seems to exist to predict the observed data. The issue is even more complicated when filler agglomeration is present. To achieve this goal, we invoke a two-scale agglomerate-based homogenization scheme to address the issue of filler agglomeration and a thermodynamically driven temperature-degraded process to describe the interface effect. Time-temperature superposition principle with a reduced time scale is also employed for the polymer matrix. Several key microstructural features including graphene volume concentration, aspect ratio, and dispersion state of nanofillers in the graphene-rich agglomerates and the graphene-poor matrix are all considered. The theory is developed in the Laplace transformed space. It is shown that the predicted creep strain of a graphene/polystyrene nanocomposite is significantly enhanced with the increase of temperature, but its recovery strain remains relatively flat. Graphene loading notably decreases the overall creep, but filler agglomeration and temperature-degraded process both greatly enhance it. The calculated results are all in close agreement with experiments. This work could provide guidance for tailoring creep and recovery properties of graphene nanocomposites by temperature. • Derive the thermodynamics-based evolution equation for temperature-degraded process of imperfect interlayer. • Evaluate temperature-dependent creep and recovery of agglomerated graphene nanocomposite via two-scale homogenization scheme. • Investigate the influence of microstructural parameters on the temperature-dependent effective viscoelastic characteristics. [ABSTRACT FROM AUTHOR]