Research of freezing kinetics of water drop on superhydrophobic coating surfaces

Introduction. Anti-icing coatings are used to prevent icing of the building roofs and power transmission line poles. One of the characteristics of anti-icing properties of superhydrophobic surfaces is the delay in the crystallization of drops on such surfaces. A significant delay in the crystallization of water drops on superhydrophobic substrates is noted in the scientific and technical literature. However, it is recorded in a number of papers that the delay time of crystallization on hydrophilic substrates is longer than the corresponding values on superhydrophobic surfaces. In connection with the foregoing, the study of the freezing kinetics of a water drop on a superhydrophobic surface in order to assess its efficiency is a relevant scientific and technical problem. Materials and methods. To evaluate the kinetics of freezing a of water drop on a superhydrophobic surface, the following experiment is conducted. A drop of water is placed on the superhydrophobic surface of the mortar substrate, which is placed in a freezer at a temperature of –18 °C. Studies of the drop freezing dynamics on the surface are performed using a Testo 875-1 thermal imager. To create a superhydrophobic surface, an aerosil R 972 with density ρ = 2360 kg/m3, particle size of 16 nm and specific surface area Ssp = 12 000 m2/kg is used as a filler. A silicone resin SILRES® MSE 100 of 10 % concentration is used as a binder. The obtained solutions are deposited on the mortar substrates. The degree of hydrophobicity is assessed by the magnitude of the wetting angle (θ°). Results. Results of the studies of temperature distribution on the water drop surface indicate that the distribution is uneven. The process of drop freezing is multistage. In the initial period, there is a transfer of heat from the surface into the water drop. This stage is followed by the process of drop freezing which is manifested in the upward movement of the freezing front from the substrate. Conclusions. It is revealed that the temperature distribution on the surface of a water drop is uneven. When freezing, a water drop has a pointed top.