We study frost formation and its impact on icephobic properties of superhydrophobic surfaces. Using an environmental scanning electron microscope, we show that frost nucleation occurs indiscriminately on superhydrophobic textures without any particular spatial preference. Ice adhesion measurements on superhydrophobic surfaces susceptible to frost formation show increased adhesion over smooth surfaces with a strong linear trend with the total surface area. These studies indicate that frost formation significantly compromises the icephobic properties of superhydrophobic surfaces and poses serious limitations to the use of superhydrophobic surfaces as icephobic surface treatments for both on-ground and in-flight applications.

Heterogeneous nucleation of water plays an important role in a wide range of natural and industrial processes. Though heterogeneous nucleation of water is ubiquitous and an everyday experience, spatial control of this important phenomenon is extremely difficult. Here we show for the first time that spatial control in the heterogeneous nucleation of water can be achieved by manipulating the local nucleation energy barrier and nucleation rate via the modification of the local intrinsic wettability of a surface. Such ability to control water nucleation could address the condensation-related limitations of superhydrophobic surfaces and has implications for efficiency enhancements in energy and desalination systems.

This paper studies the impinging droplets on superhydrophobic textured surfaces and proposes a design guideline for nonwetting surfaces under droplet impingement. A new wetting pressure, the effective water hammer pressure, is introduced in the study to clearly define wetting states for the impinging droplets. This approach establishes the design criteria for nonwetting surfaces to impinging droplets. For impingement speed higher than raindrop speed, the surfaces need to have sub-100-nm features to generate a large enough antiwetting pressure for the droplets to take a nonwetting state after impingement.

The effect of surface energies, strains, and stresses on the size-dependent elastic state of embedded inhomogeneities are investigated. At nanolength scales, due to the increasing surface-to-volume ratio, surface effects become important and induce a size dependency in the otherwise size-independent classical elasticity solutions. In this letter, closed-form expressions are derived for the elastic state of eigenstrained spherical inhomogeneities with surface effects using a variational formulation. Our results indicate that surface elasticity can significantly alter the fundamental nature of stress state at nanometer length scales. Additional applications of our work on nanostructures such as quantum dots, composites, etc. are implied.

We have studied the band-gap variation and stability energy in silicon carbide ͑SiC͒ nanoclusters of different polytypes using density functional theory ͑DFT͒ based on a gradient-corrected approximation. We have obtained a series of spherical SiC nanoclusters with dimensions up to 2 nm from bulk 2H, 3C, and 4H polytype crystals. All clusters with diameters smaller than 1 nm exhibit similar energy-gap-size variations, while energy gaps for clusters larger than 1 nm show a distinct size dependence with different polytypes and approach their bulk gaps with an increase in cluster size. In contrast to their bulk behavior, the binding energy difference between polytypes of clusters within the diameter range 0.5 nm− 2 nm is found to be negligible, suggesting that the problems associated with the synthesis of polytypes of SiC in bulk may disappear for small clusters. The convergence of the energy gap and binding energy with different polytypes at small size clusters and the transition between the clusters to bulk behavior in SiC systems could be exploited for making future nano-optoelectronics devices.