Sliding and rolling behavior of water droplets on an ordered nanoball matrix fluorocarbon polymer layer under simulated weather conditions

Ordered nanoball matrix fluorocarbon polymer layers were produced with two different fluorocarbon polymers on an anodized aluminum oxide (AAO) surface. These treated surfaces each exhibited hydrophobicity or superhydrophobicity. The dynamic behavior of a droplet sliding down these surfaces was captured by high-speed photography under simulated weather conditions including at room temperature (25°C) and low temperature (5°C) with various relative humidities (30%-80%). By analyzing the trajectory of a marker in the captured video frame-by-frame, we distinguished the slipping and rolling behaviors and analyzed the internal fluidity by calculating the ratio of these two motions. Both the pore diameters of the substrate matrix and the environmental conditions play a dominant role in the resultant sliding acceleration of a water droplet. At room temperature (25°C) and 30% relative humidity, the sliding acceleration of the droplet on the fluoropolymer layer decreased by 0.5 m·s−2 -0.6 m·s−2 as the pore diameters of the underlying AAO substrates increased. The sliding acceleration underwent a 25%-50% decrease under extreme environmental conditions (5°C and 80% RH). These phenomena proved that a wetting transition from the Cassie-Baxter model to the Wenzel model can partially occur under various weather conditions.