Visualizing Elastocapillary Expansion of Graphene through Bulge Tests

The expansion or shrinkage of elastic membranes when wetted by liquids has long been a theoretical concept, yet remained untested due to the extremely small in-plane deformations involved. Here, we leverage out-of-plane bulging to verify that water wetting can indeed cause graphene bubbles to expand. Notably, we find that the graphene bubble becomes "softer" when in contact with water. By incorporating surface tension into Vlassak's model, we obtain a revised equation that accurately attributes the expansion of graphene to the reduction of surface tension at the graphene-water interface. Furthermore, we exploit the underlying principle to actively program deformation and vibrational dynamics of graphene membranes by applying an electric field at the solid-liquid interface. Our results provide fundamental mechanistic insights into the crucial role of surface tension for elastic membranes and open up new avenues for designing responsive structures driven by surface tension.