Superhydrophobicity mechanism of refoliated quaking aspen leaves after complete defoliation by LDD (gypsy, spongy) moth caterpillars.

Complete defoliation of trees due to periodic LDD (Lymantria dispar dispar) moth outbreaks in many parts of the world is a significant stress factor for the survival of individual trees and entire forests over vast areas. This study addresses such a mid-summer defoliation event in Ontario, Canada for quaking aspen trees during 2021. It is shown that complete refoliation in the same year is possible for these trees, albeit with significantly smaller leaf size. Regrown leaves showed the well-known non-wetting behaviour typically observed for the quaking aspen tree without a defoliation event. These leaves have the same hierarchical dual-scale surface structure consisting of nanometre-size epicuticular wax (ECW) crystals superimposed on micrometre-sized papillae. This structure provides for the Cassie-Baxter non-wetting state with a very high water contact angle on the adaxial surface of the leaves. Subtle differences in the leaf surface morphology of the refoliation leaves compared with the regular growth leaves are likely due to environmental factors such as seasonal temperature during the leaf growth period after budbreak.

Thermally Robust Non-Wetting Ni-PTFE Electrodeposited Nanocomposite.

The effect of high temperature exposure on the water wetting properties of co-electrodeposited superhydrophobic nickel-polytetrafluoroethylene (Ni-PTFE) nanocomposite coating on copper substrates was studied. This was accomplished by comparing the performance with a commercial superhydrophobic spray treatment (CSHST). The Ni-PTFE and CSHST coatings were both subjected to heating at temperatures up to 400 °C. Results showed that the Ni-PTFE was able to maintain its superhydrophobicity throughout the entire temperature range, whereas the CSHST became more wettable at 300 °C. Furthermore, additional abrasive wear tests were conducted on both materials that were subjected to heating at 400 °C. The Ni-PTFE remained highly non-wettable even after 60 m of abrasion length on 800 grit silicon carbide paper, whereas the CSHST coating was hydrophilic after 15 m.

Mesostructure of Ordered Corneal Nano-nipple Arrays: The Role of 5-7 Coordination Defects.

Corneal nano-nipple structures consisting of hexagonally arranged protrusions with diameters around 200 nm have long been known for their antireflection capability and have served as biological blueprint for solar cell, optical lens and other surface designs. However, little is known about the global arrangement of these nipples on the ommatidial surface and their growth during the eye development. This study provides new insights based on the analysis of nano-nipple arrangements on the mesoscale across entire ommatidia, which has never been done before. The most important feature in the nipple structures are topological 5- and 7-fold coordination defects, which align to form dislocations and interconnected networks of grain boundaries that divide the ommatidia into crystalline domains in different orientations. Furthermore, the domain size distribution might be log-normal, and the domains demonstrate no preference in crystal orientation. Both observations suggest that the nipple growth process may be similar to the nucleation and growth mechanisms during the formation of other crystal structures. Our results are also consistent with the most recently proposed Turing-type reaction-diffusion process. In fact, we were able to produce the key structural characteristics of the nipple arrangements using Turing analysis from the nucleation to the final structure development.

Recent Advances in Superhydrophobic Electrodeposits.

In this review, we present an extensive summary of research on superhydrophobic electrodeposits reported in the literature over the past decade. As a synthesis technique, electrodeposition is a simple and scalable process to produce non-wetting metal surfaces. There are three main categories of superhydrophobic surfaces made by electrodeposition: (i) electrodeposits that are inherently non-wetting due to hierarchical roughness generated from the process; (ii) electrodeposits with plated surface roughness that are further modified with low surface energy material; (iii) composite electrodeposits with co-deposited inert and hydrophobic particles. A recently developed strategy to improve the durability during the application of superhydrophobic electrodeposits by controlling the microstructure of the metal matrix and the co-deposition of hydrophobic ceramic particles will also be addressed.

Remarkable crystal and defect structures in butterfly eye nano-nipple arrays.

The corneal nipple structures on the eyes of two nymphalid butterfly species (Nymphalis antiopa and Polygonia interrogationis) are analyzed in terms of nipple arrangements and associated defects. The nipple arrays in both species have close-packed hexagonal lattices with lattice parameters of about 200 nm. The most abundant defects observed are 5-7 coordination defects that generate dislocations, dislocation-type low angle and structural unit-like high angle grain boundaries, as well as closed-loop defects. These disordered structures are compared with imperfections found in other 2D and 3D crystal structures, and it is concluded that the defects in the nipple arrays are likely not due to random growth accidents. Instead, they could be the result of geometric constraints due to eye curvature or serve a yet undiscovered purpose in the optical properties of these eyes.

Grain boundaries and coincidence site lattices in the corneal nanonipple structure of the Mourning Cloak butterfly.

In this study the highly ordered corneal nanonipple structure observed on the Mourning Cloak butterfly (Nymphalis antiopa) is analyzed with a particular emphasis on the high-angle grain-boundary-like defects that are observed between individual nanonipple crystals. It is shown that these grain boundaries are generated by rows of topological coordination defects, which create very specific misorientations between adjacent crystals. These specific orientations form coincidence site lattices, which (i) have unit cells larger than the unit cell in each individual crystal and (ii) extend from one crystal to the next, effectively creating order over areas larger than the individual crystals. A comparison to similar coincidence site lattices in engineering materials is made and the importance of such arrangements in terms of nipple packing density, corneal lens curvature and potential optical properties is discussed.