On the universality of shapes of the freezing water droplets

The freezing of water droplets placed on metallic surfaces and surfaces lubricated with various silicone oils was studied. The freezing of water droplets placed on inclined and upside-down planes, both bare and coated with silicone oil (that completely coated the water droplets) was also studied. We established that the opening angle of the freezing cone did not depend on neither the spatial orientation of the substrate nor on the coating of the frozen droplet with the silicone oil. The geometrical axis of the freezing cones coincided with the normal to the inclined surface. The opening angle of the freezing tip was not influenced by the volume of the droplet, contact angle hysteresis, the pinning of the triple line, the surface tension of the cloaked droplet, the viscosity of the silicone oil and the spatial orientation of the substrate. The paper supports the universal mechanism of the formation of the freezing tip, based on purely geometrical considerations.