Interface-derived extraordinary viscous behavior of exfoliated graphite

Exfoliated graphite is obtained by the rapid heating of acid-intercalated graphite flakes. It exhibits a cellular microstructure, with about 60 graphite layers in the cell wall. The recently reported extraordinarily strong viscous behavior of the exfoliated graphite and its cement-matrix composite has been explained in this paper in terms of an interface-derived viscous mechanism, which is in contrast to the well-known bulk viscous deformation mechanism that rubber exhibits. The interfacial mechanism is associated with the dynamic sliding at low amplitudes between the graphite layers in the cell wall of exfoliated graphite during dynamic loading in the elastic regime. The ease of sliding is enabled by the loosening of the interlayer interface that has occurred during exfoliation, in which the cell wall extends greatly like a balloon due to extensive sliding between the graphite layers in the cell wall. The viscous behavior is consistent with the well-known resiliency of flexible graphite, which is a sheet made by greatly compressing exfoliated graphite without a binder. In the cement-matrix composite, the exfoliated graphite is sandwiched with sufficient tightness by the cement matrix in the microstructure of the composite, thereby providing constrained-layer damping in the microscale.