Statistically understanding the roles of nanostructure features in interfacial ice nucleation for enhancing icing delay performance.

Freezing is a spontaneous phase transformation process, which is mainly governed by heterogeneous ice nucleation. This work aims at the discussion of the roles of nanostructure geometrical features in interfacial ice nucleation. Two kinds of superhydrophobic nanostructures with sealed layered porous and open cone features were designed and fabricated by means of wet-chemical processing methods. Both the resultant surfaces exhibited a larger extent of improvement of non-wettability, especially in the aspect of droplet movement. Comparing with the sealed layered nanoporous structures, the open nanocone structures only induced a sliding angle of 1°. During the freezing process, the solid-liquid contact type highly determined the macroscopic freezing process, and resulted in a difference of icing delay time of ∼170 s (and freezing temperature of ∼3.7 °C) between both superhydrophobic nanostructures. Also, the precooling time, the period before the moment of a droplet instantaneously becoming turbid, occupied a dominant role (∼90%) in the entire freezing time. The ice nucleation behavior was analyzed in detail according to the statistical results of 500 cycles of freezing temperatures, demonstrating that the ice nucleation probability of nanocone structures is less than that of layered nanoporous structures. This is in line with the ice nucleation temperatures of both as-prepared superhydrophobic nanostructures. As a consequence, there was a greater distinction in the ice nucleation rate, especially in the solid-liquid interface nucleation rate, by two orders of magnitude.

Spraying Fabrication of Durable and Transparent Coatings for Anti-Icing Application: Dynamic Water Repellency, Icing Delay, and Ice Adhesion.

Anti-icing/icephobic coatings, typically applied in the form of surface functional materials, are considered to be an ideal selection to solve the icing issues faced by daily life and industrial production. However, the applications of anti-icing coatings are greatly limited by the two main challenges: bonding strength with substrates and stability of the high anti-icing performance. Here, we designed and fabricated a kind of high-performance superhydrophobic fluorinated silica (F-SiO2)@polydimethylsiloxane coatings and further emphasized the improvement of the bonding strength with substrates and the maintenance of high anti-icing performance. The resultant coatings exhibited excellent water repellency with a contact angle up to 155.3° and a very short contact time (∼10.2 ms) of impact droplets. At low temperatures, the coming droplets still rapidly rebounded off the coating surface, and the superhydrophobic coatings displayed a more than 50-fold increase of freezing time comparing with bare aluminum. The ice adhesion strength on the coatings was only 26.3 kPa, which was far less than that (821.9 kPa) of bare aluminum. Furthermore, the nanoporous structures constructed by anodic oxidation could tremendously enhance the bonding strength of the coatings with the substrate, which was evaluated through a standard method (ASTM D3359). The anti-icing properties still retained high stability under the conditions of 30 icing/deicing cycles, soaking, and scouring of acid solution (pH = 5.6). This work can effectively push the anti-icing coatings toward a real-world application.