Freezing delay of sessile drops: Probing the impact of contact angle, surface roughness and thermal conductivity

Elucidating the predominant factors for the freezing delay of surfaces is still a matter of discussion and controversy. Freezing delay is explained in literature through the classical nucleation theory. It postulates that freezing delay of a surface is enhanced with low surface roughness and sessile drops of high contact angles. However, since surface roughness influences the wetting properties, a better understanding of how each factor affects the freezing delay requires to uncouple both effects systematically. This is indeed the reason why certain contradictions are found in literature. Besides, some works report that further factors, such as the surface-to-drop heat transfer might also be important. In this work, we analyzed independently how drop geometry, surface roughness and thermal conductivity influence the freezing delay of solid surfaces at unsaturated conditions. Our results show that the drop contact angle and surface roughness strongly influences the freezing delay on conductive and insulating materials. Although its importance is minor, we also found that conductive materials delay freezing more efficiently than insulating materials. In conclusion, our results point out that conductive, smooth and hydrophobic surfaces are the most efficient surfaces to delay freezing in unsaturated environments.