Understanding the Role of Surface Micro-Texture on the Delayed Freezing of Drops on Cold Surfaces

Freezing of drops on surfaces has many consequences in icing of various systems, e.g. micro-condensers. It is known that when a water drop is placed on a cold surface and the surface temperature is reduced, it will not necessarily freeze when the surface temperature has reached zero degrees Celsius. The delay in freezing of a drop on a cold surface is not well understood; especially the effect that micro- and nano-texture of a surface has this delay. In this study, freezing and melting points of water drops on various micro-textured surfaces, i.e. superhydrophilic, and superhydrophobic have been measured by differential scanning calorimetry (DSC). A comparison of the experimental results with smooth hydrophilic and hydrophobic surfaces allows us to understand the roles of surface chemistry and roughness in freezing of drops in contact with such surfaces. It is found that when the surface chemistry is hydrophobic, roughness will delay the freezing and a drop may not freeze until the surface temperature has been lower than −15 ° C. On the contrary, for hydrophilic surfaces, roughness will shorten the freezing delay and facilitate formation of ice on the surface. This can explain the benefit of the superhydrophobic surfaces (SHS) in preventing ice formation.