Thermal Stability Evaluation and Analyses of Bionic Drop-Jumping Superhydrophobic Copper Nanocone Structure Surface

The thermal stability of bionic superhydrophobic drop-jumping copper nanostructure surfaces is key to ensuring their safe use in the chip-cooling field. However, there is no report about the allowable heating temperature limit of such functional surfaces, and the condensate mode and wettability evolution vary with heating temperature (T), which are still unclear. Here, we demonstrate for the first time that both the macroscopic drop nonsticky superhydrophobicity and condensate microdrop self-jumping removal functions of the superhydrophobic copper nanocone array structure surface can remain stable as long as T is no more than 150 °C, which is far higher than the allowable temperature limit (45 °C) of 5G mobile phone chips and sufficient to develop matchable low-temperature (e.g., 100-140 °C) soldering technologies. As T rises up to 175, 200, and 300 °C, the sample surface presents sticky superhydrophobicity, ordinary hydrophobicity, and superhydrophilicity for macroscopic water drops, accompanied by the progressive transition of condensate dynamics toward the microdrop coalescence/pinning, dropwise condensation, and filmwise condensation. Decoupling thermal stability analyses into the morphology change of copper nanocones and the dissociation degrees of thiol bonds at different temperatures indicates that the thermal stability of superhydrophobic copper nanostructure depends on the latter rather than the former. Copper nanocones and their bonded thiol can remain stable as T ≤ 500 °C and T ≤ 150 °C, respectively. Higher heating temperature results in the gradual dissociation of thiol bonds until complete decomposition. Such temperature-dependent performance stability and instability can be rationalized by combined experiments and analyses. This work not only helps deepen the thermal stability understanding of superhydrophobic metal nanostructures but also identifies the safe use temperature limit of octadecanethiol-modifed copper nanostructures, which opens a door for developing matchable low-temperature packaging technologies and next-generation high-performance ultrathin copper vapor chambers integrated with the superhydrophobic drop-jumping function in the near future.