On the dynamics of contact line freezing of water droplets on superhydrophobic carbon soot coatings

Despite the opportunity to manipulate the water freezing via superhydrophobic materials, their commercial use for passive icing protection is still questioned, since the combined effect of surface morphology, air cushion arrangement, roughness, chemistry and film thickness on the icephobic properties of a given non-wettable solid remains unexplored. This article addresses the existing research gaps by studying the ice nucleation dynamics at the contact line of various superhydrophobic soot-based surfaces, potentially applicable in cryobiology for enhancing the existing cryopreservation technologies. We examine the freezing time and freezing temperature of water droplets settled on three groups of soot coatings with divergent morphochemical features, adjusted by modifying the samples with alcohol, fluorocarbon and/or silver hydrogen fluoride. Our results demonstrate the appearance of a new “contour” freezing mode, where the droplet shell crystallizes simultaneously with the contact interface, whilst the soot's chemical bonds along with some of its physical characteristics govern the ice formation.