Compact nanoscale textures reduce contact time of bouncing droplets

Many natural surfaces are capable of rapidly shedding water droplets—a phenomenon that has been attributed to the presence of low solid fraction textures (Φs ~ 0.01). However, recent observations revealed the presence of unusually high solid fraction nanoscale textures (Φs ~ 0.25 to 0.64) on water-repellent insect surfaces, which cannot be explained by existing wetting theories. Here, we show that the contact time of bouncing droplets on high solid fraction surfaces can be reduced by reducing the texture size to ~100 nm. We demonstrated that the texture size–dependent contact time reduction could be attributed to the dominance of line tension on nanotextures and that compact arrangement of nanotextures is essential to withstand the impact pressure of raindrops. Our findings illustrate a potential survival strategy of insects to rapidly shed impacting raindrops, and suggest a previously unidentified design principle to engineering robust water-repellent materials for applications including miniaturized drones.

Precursor Nanoscale Textures in Ferroelastics: Interplay between Anisotropy and Disorder

We study the effect of anisotropy and disorder on the morphology of precursor microstructures within a Ginzburg-Landau free energy framework. In addition, with increasing disorder at low anisotropy we find a crossover from a twinned state to a non-transforming frozen state. Results are compared with available experimental data.

Atmosphere Effects on the Machinability of Cutting Tools with Micro- and Nanoscale Textures

Cutting and friction experiments were conducted in various atmospheres to investigate the chemical effect on textured cutting tools. The cutting experiments indicated that the atmosphere affected the machinability of the textured tools; a larger effect was observed in the presence of gas such as oxygen. A ball-on-disk friction apparatus was developed and used for the friction experiments. Smaller friction coefficients were observed in the presence of oxygen, a trend similar to that observed during the cutting experiments. These results indicate that oxidation is an important factor in determining the texture effect for machining aluminum alloy.