Experimental study on developing in-situ hierarchical micro/nanocrystals for improved capillary wicking

The superior capillary wicking capability of hierarchical surfaces determined by the capillary pressure and viscous resistance plays a critical role in developing the high-efficient thermal management devices. In this study, a novel chemical oxide method for fabricating the in situ micro/nanocrystal structures on the copper substrates with prominently improved capillary wicking capability is proposed. Single-scaled and hierarchical structures can be fabricated, and the capillary wicking capability of the hierarchical structures exhibits the much higher wicking coefficient than that of the single-scaled structures. The wicking coefficient on the nanosheet and micro-flowers hierarchical surface was measured as 3.77 mm/s0.5, which indicates a maximum improvement of 146.4% compared to single-scaled structures. This hierarchical structure can provide two-tier pores for strengthening the capillary pressure driven by the nanoscale pores and reducing the viscous resistance driven by the micropores. It is worth noting that the ultrafast wicking on the hierarchical surface is useful in creating extremely effective thermal management systems and advanced heat exchangers.