  The adhesion of two-dimensional (2D) materials to other surfaces is so far
believed to be a solid-solid mechanical contact. Here, we conduct both
atomistic simulations and theoretical modeling to show that there exists a
reversible conversion of energy between thermal and mechanical work in the
attachment/detachment of 2D materials on/off a surface, indicating that 2D
materials adhesion is fundamentally like gas adsorption rather than solid
adhesion. We reveal that the underlying mechanism of this intriguing gas-like
adhesion for 2D materials is the entropy difference between their freestanding
and adhered states. Both the theoretical model and atomistic simulations
predict that adhesion induced entropy difference increases with increasing
adhesion energy and decreasing equilibrium binding distance. The present
findings provide a fundamental guidance toward understanding the adhesion of 2D
materials, which is important for designing 2D materials based devices and may
have general implications for nanoscale efficient energy conversion.
