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 fi ber
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.
