Exceptional negative thermal expansion and viscoelastic properties of graphene oxide paper

We report unusual negative thermal expansion and viscoelastic properties in graphene oxide paper. The paper was prepared from aqueous GO dispersions using a simple vacuum evaporation technique. From room temperature to 150 °C, this paper-like graphene oxide sheet exhibits a constant negative thermal expansion coefficient of −67 × 10−6/°C along the in-plane direction. Peculiar hysteresis loops of thermal expansion-temperature curves are observed, which are affected by the cooling rate and starting temperature of cooling. The tensile tests on GO paper show clear hysteresis loops, revealing the viscoelastic property of the paper. The viscoelastic properties show excellent frequency-stability in the range of 1.0–60 Hz. In the low temperature range −150 to 25 °C, however, they show a strong temperature dependence. The storage modulus of the graphene oxide paper continuously increases with decreasing temperature.