Elastomeric behavior of exfoliated graphite, as shown by instrumented indentation testing

This paper reports for the first time the elastomeric behavior of a non-polymeric material, as observed in exfoliated graphite compacts (⩽12 vol.% solid, preferably 4 vol.% solid) and enabled by the high-amplitude reversible and easy sliding of the graphite layers within the cell wall of exfoliated graphite. The reversibility is probably due to the cellular structure of exfoliated graphite. The elastomeric character is independent of the maximum load and essentially unchanged upon reloading. The total and reversible engineering shear strains of the cell wall (∼60 graphite layers, ∼20 nm thick) are up to 40 and 35 respectively during instrumented indentation (in the compaction direction) without fracture of the layers, compared to corresponding values of 12 and 8 for flexible graphite (38 vol.% solid). The fraction of displacement that is irreversible is as low as 12%, compared to 29% for flexible graphite. The modulus is as low as 83 kPa, compared to 790 kPa for flexible graphite. The greater the degree of compaction, the lower are the shear strain and reversibility, and the higher are the modulus and the displacement load. The ease of interlayer sliding is inadequate in flexible graphite or highly-oriented pyrolytic graphite (prior work) for substantial elastomeric behavior.