Hierarchical structures in nature provide unique functions for living organisms that can inspire technology. Nanoscale hierarchical structured surfaces are essential to realize the dual functions of non-wetting and transparency for...

Metal-oxide sensors, detect gas through the reaction of surface oxygen molecules with target gases, are promising for the detection of toxic pollutant gases, combustible gases, and organic vapors; however, their sensitivity, selectivity, and long-term stability limit practical applications. Porous structure for increasing surface area, adding catalyst, and altering the operation temperature are proposed for enhancing the sensitivity and selectivity. Although humidity can significantly affect the property and stability of the sensors, studies focusing on the long-term stability of gas sensors are scarce. To reduce the effects of humidity, 1H, 1H, 2H, 2H–perfluorooctyltriethoxysilane (PFOTS) was coated on a porous SnO2 film. The interconnected SnO2 nanowires improved the high surface area, and the PFOTS coating provided superhydrophobicity at water contact angle of 159°and perfect water vapor repellency inside E-SEM. The superhydrophobic porous morphology was maintained under relative humidity of 99% and operating temperature of 300 °C. The CO gas sensing of 5, 20, and 50 ppm were obtained with linearity at various humidity. Flame detection was also achieved with practical high humidity conditions. These results suggest the simple way for reliable sensing of nanostructured metal-oxide gas sensors with high sensitivity and long-term stability even in highly humid environments.

Polymer heat exchangers have drawn attention due to their special characteristics such as flexibility, low weight, corrosion, and bio-fouling resistance, as well as their ease of manufacturing. However, since their thermal conductivity is low, they require a way to increase their heat transfer rate. We investigated the effect of modifying the surface wettability of polymer films on the heat transfer rate during the condensation process, both theoretically and experimentally. Condensed water formation on the film surface depends on the surface wettability control, and thus, hydrophilic or hydrophobic surfaces can induce film-wise or drop-wise condensation, respectively. Generally, the polymer surface shows a hydrophobic property due to the intrinsic C-C and C-H bonding of polymer frames. Here, we used four different types of polymer films, which have different thermal conductivity and controlled wettability properties, including polyimide film, polyimide film containing aluminum nanoparticles, and both films with super-hydrophobic treatment. The results show that nanostructured polymers with hydrophobic treatment have a 25% lower wetted area fraction than those without hydrophobic treatment, independent of the thermal conductivity of the polymer films. To compare the heat transfer rates, we designed a thermal resistance model considering vapor convection, vapor-water interfaces and curvatures, and conductions of the droplet, nanostructure, and polymer. We found that the convective thermal resistance dominantly affects the heat transfer rate and treated polymers showed over 200% higher total heat transfer than bare polymer.