Effects of Low Temperature and Humidity on Contact Angles of Water Droplets on Superhydrophobic Surfaces

The Cassie-Wenzel(C-W) wetting transition on superhydrophobic surfaces has been extensively explored. However, the influence of environmental humidity on wettability transformation of irregular surface formed by film mulch is not sufficiently explored. The static contact angle changes of water droplets induced by different temperature and ambient humidity were studied by ground cold environment test. The results show that low temperature induces the drop contact angle to decrease, and the surface condensation occurs. After the temperature is stabilized, humidity becomes the main factor affecting the change of contact angle The results show that the superhydrophobic surface condenses when the temperature decreases, and humidity becomes the main factor affecting the change of contact angle when the temperature stabilizes. The freezing delay time and contact angle before freezing are affected by different temperature. The effects of temperature and humidity on the contact angle can be quantitatively obtained by low temperature and freezing test of water droplet. The contact angle decreases by 5° ± 1.7° for every 5 °C decrease in temperature. When the temperature is stabilized, the contact angle of water droplets decreases by 2.4° ± 0.7° per minute at 88%RH and by 0.9° ± 0.2° per minute at 45%RH.