We study the elastic response of graphene nanomeshes based on molecular-statics and molecular-dynamics simulations of uniaxial tensile deformation tests. Elastic properties are determined as a function of the nanomesh architecture, namely, the lattice arrangement of the pores, pore morphology, material density (ρ), and pore edge passivation, and scaling laws for the density dependence of the elastic modulus M, M(ρ), are established. We find that, for circular unpassivated pores, M scales with the square of ρ. Deviations from quadratic scaling are most strongly influenced by pore morphology and, to a lesser extent, by pore edge passivation and temperature.

The barocaloric effect (BCE) is characterized as thermal responses (variations of temperature or entropy) in a material resulting from compression. Several materials exhibit a BCE suitable for development of solid-state cooling devices, typically associated with pressure-induced phase transitions. A giant BCE has been observed for natural rubber (NR), which makes it a cheap and environmentally friendly candidate for such a purpose. The reason for the significant BCE in NR is still elusive, considering that there is no evidence of phase transitions in the process. The present study uses a combination of classical molecular dynamics (MD) simulations and a thermodynamic analysis to investigate the origin of the giant BCE in NR. MD simulations of adiabatic compression cycles for NR were carried out under varied applied pressures and initial temperatures and were able to capture the BCE. A detailed analysis of the results helped us to elucidate the structural transformations and resulting energy changes in the material under compression. MD results for isothermal compression along with the thermodynamic analysis showed that the high compressibility of NR combined with an unusual decrease in the potential energy at the molecular level upon compression favors significantly the BCE (quantified by isothermal entropy changes and adiabatic temperature changes in the process), a feature not commonly seen in other materials. These findings can be extended to other polymers and are certainly going to be useful toward the design of materials with an enhanced BCE.

In this work we present a combination of experimental, theoretical and computational analysis to demonstrate the colossal barocaloric (BC) effect in long-chain linear n-alkanes (paraffins). Adiabatic compression experiments with eicosane...

We report results of a comprehensive computational study of the mechanical response to nanoindentation of graphene nanomeshes (GNMs) or nanoporous graphene, namely, single-layer graphene sheets with periodic arrangements of nanopores, based on molecular-dynamics simulations of nanoindentation tests according to a reliable interatomic bond-order potential. We find the GNMs’ response to indentation to be nonlinearly elastic until fracture initiation, with elastic properties that depend strongly on the GNM porosity but are not sensitive to pore edge passivation, which, however, influences the GNM failure mechanism past fracture initiation. Increasing GNM porosity leads to a monotonic decrease of the 2D elastic modulus of the GNMs, and the modulus–porosity dependence follows a quadratic scaling law. The maximum stress reached at the GNM breaking point is high throughout the porosity range examined, even at very high porosity. The maximum deflection of the indented GNMs at their breaking point exhibits a minimum at porosities below 20%; beyond this critical porosity, the maximum deflection increases monotonically with increasing porosity and can reach values comparable to half of the indented sample radius at high porosities. Such high deformability is interpreted on the basis of the C–C bond length and stress distribution over the GNM at its breaking point. Moreover, our analysis reveals an inelastic, dissipative necking mechanism of GNM failure at high porosities that further enhances the excellent deformability of the GNMs. Our findings highlight the potential of graphene nanomeshes as 2D mechanical metamaterials whose mechanical response can be tuned by proper tailoring of their structural features.

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