Pinning in a Contact and Noncontact Manner: Direct Observation of a Three-Phase Contact Line Using Graphene Liquid Cells

Pinning of a three-phase contact line at the nanoscale cannot be explained by conventional macro-scale theories, and thus requires an experimental insight to understand this phenomenon. We performed in-situ TEM observation of the three-phase contact lines of bubbles inside graphene liquid cells to experimentally investigate the causes of nanoscale pinning. In our observations, the three-phase contact line was not affected by the 0.6 nm-thick inhomogeneity of the graphene surface, but thicker metal nanoparticles with diameters of 2–10 nm and nano-flakes caused pinning of the gas-liquid interface. Notably, we found that flake-like objects can cause pinning that prevents the bubble overcome the flake object in a non-contact state, with a 2-nm-thick liquid film between them and the bubble. This phenomenon can be explained by the repulsive force obtained using the Derjaguin, Landau, Verwey, and Overbeek theory. We also observed the flake temporally prevented the gas-liquid interface moving away from the flake. We discussed the physical mechanism of the attractive force-like phenomenon by considering the nanoconfinement effect of liquid sandwiched by two graphene sheets and the hydration layer formed near the solid surface

Nanoscale Bubble Dynamics Induced by Damage of Graphene Liquid Cells

Graphene liquid cells provide the highest possible spatial resolution for liquid-phase transmission electron microscopy. Here, in graphene liquid cells (GLCs), we studied the nanoscale dynamics of bubbles induced by controllable damage in graphene. The extent of damage depended on the electron dose rate and the presence of bubbles in the cell. After graphene was damaged, air leaked from the bubbles into the water. We also observed the unexpected directional nucleation of new bubbles, which is beyond the explanation of conventional diffusion theory. We attributed this to the effect of nanoscale confinement. These findings provide new insights into complex fluid phenomena under nanoscale confinement