Hierarchical, Dual-Scale Structures of Atomically Thin MoS2 for Tunable Wetting

Molybdenum disulfide (MoS2), a well-known solid lubricant for low friction surface coatings, has recently drawn attention as an analogue two-dimensional (2D) material beyond graphene. When patterned to produce vertically grown, nanoflower-structures, MoS2 shows promise as a functional material for hydrogen evolution catalysis systems, electrodes for alkali metal-ion batteries, and field-emission arrays. Whereas the wettability of graphene has been substantially investigated, that of MoS, structures, especially nanoflowers, has remained relatively unexplored despite MoS2 nanoflower's potential in future applications. Here, we demonstrate that the wettability of MoS2 can be controlled by multiscale modulation of surface roughness through (1) tuning of the nanoflower structures by chemical vapor deposition synthesis and (2) tuning of microscale topography via mechanical strain. This multiscale modulation offers broadened tunability (80-155 degrees) compared to single-scale tuning (90-130 degrees). In addition, surface adhesion, determined from contact angle hysteresis (CAH), can also be tuned by multiscale surface roughness modulation, where the CAH is changed in range of 20-40 degrees Finally, the wettability of crumpled MoS, nanoflowers can be dynamically and reversibly controlled through applied strain (similar to 115-150 with 0-200% strain), and remains robust over 1000 strain cycles. These studies on the tunable wettability of MoS, will contribute to future MoS2-based applications, such as tunable wettability coatings for desalination and hydrogen evolution.