Understanding the frosting and defrosting mechanism on the superhydrophobic surfaces with hierarchical structures for enhancing anti-frosting performance

Abstract

To ascertain the inhibiting-frost ability of superhydrophobic surfaces, the processes of frosting and defrosting were observed on four surfaces with different microstructure topography-features in this work. Comparing with the untreated hydrophobic surface, the superhydrophobic microstructure surface exhibited superior anti-frosting performance. Besides, this work demonstrated that the anti-frosting property was sensitive to surface microscopic structure, since microstructures could induce to trap air pockets underneath the droplets to produce ultra-low water adhesion and thermal insulation, resulting in a significant delay of frost formation. After frost completely being melted into pure water, the superhydrophobic surfaces significantly contributed to enhance the defrosting efficiency and the coverage fraction of remained water was only 8.5% for microblock-nanohair hierarchical structure surface. The residual droplets in Cassie-Baxter state can be facilely removed by airflow or a slight inclination, whereas the melted water mostly firmly stayed on the flat untreated surface. In addition, the comparative researches with the other structure (i.e., microblock structures and nanohair structures) surfaces further ascertained that the nanostructures on the superhydrophobic surface will contribute to the coalescence movement of microdroplets, and the primary microstructures mainly play a role in jumping or sweeping movement of the coalesced droplets.