Droplet Transport on a Nano‐ and Microstructured Surface with a Wettability Gradient in Low‐Temperature or High‐Humidity Environments

Directional driving of a droplet can be achieved on a gradient‐exhibiting, nanostructured microhump (GNMH) surface at low temperature and high humidity. The GNMH surface is fabricated using a commercial carbon fiber plate with an array of microscale hump structures; nanotechniques are used to form varying nanostructures on the microhump array, producing the micro‐ and nanostructured surface. The different nanostructures result in a wettability gradient along the surface, enabling droplet transport with the help of vibration—even at low temperature or high humidity. In contrast, simply nanostructured surfaces or microstructured surfaces that also have a wettable gradient do not enable droplet transport at low temperature or high humidty. In a range of subzero temperatures or in a range of high‐humidity conditions, the GNMH surface retains its superhydrophobicity and ability for directional droplet transport along its wettability gradient. These results may assist in the design of surfaces required for cold environments, such as microreactors, chemical analytic devices, and sensors.