Blistering at the solid-liquid interface: the graphite case-study

The mechanical swelling of a sample surface, which produces bubbles having different dimensions (from the sub-micrometer up to some tens of micrometer), is termed as blistering. This phenomenon was historically considered as a detriment of the sample surface, while, more recently, it turned out to be a model system for testing the mechanical properties of confined 3D objects. In particular, the development of blisters underneath a single layer of atoms (such as graphene) is crucial for the investigation of permeability of ultrathin sheets. In the variety of materials well-documented in the scientific literature, we present and discuss the specific case study of blister evolution on the basal plane of graphite, when the crystal undergoes an ion-intercalation during the oxidation process. Our choice is motivated by the importance of investigating graphite in an electrolytic environment, because of its electrochemical/mechanical performances that can be exploited in many applications: as an electrode in electrochemical cells, batteries, fuel-cells, but also, as a layered-crystal, in procedures for graphene production. More generally, the ion intercalation in graphite represents a model system to understand the mechanisms at molecular length-scale of the insertion of molecules inside a stratified crystal. This process, driven by electrochemistry, can be followed mainly by investigating the solid-liquid interface. Otherwise, investigating the graphite at the end of the intercalation process after emersion outside of the electrolyte leads to the observation of many residues from the solution on the graphite surface, which perturb the true morphology of blisters. In this case, rinsing the graphite surface with water would be even more perturbing, since additional chemical reactions and phenomena would alter both the chemical status and morphology of the intercalated electrode.