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

Abstract

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.