Youfa Zhang

Microscopic Observations of the Lotus Leaf for Explaining the Outstanding Mechanical Properties

The leaf of lotus (Nelumbo nucifera) exhibits exceptional ability to maintain the opening status even under adverse weather conditions, but the mechanism behind this phenomenon is less investigated. In this paper, lotus leaves were investigated using environmental scanning electron microscopy in order to illustrate this mechanism. The macro-observations show that the primary veins are oriented symmetrically from leaf center and then develop into fractal distribution, with net-shaped arrangement of the side veins. Further micro-observations show that all the veins are composed of honeycomb micro-tubes viewed from cross section, the inner of micro-tubes are patterned with extended closed-hexagons from vertical section. Different positions of leaf possess diverse mechanical properties by size variation of diameter and inner hexagons of veins, which is theoretically analyzed by building a regular honeycomb model. Specifically, the central area of lotus tends to be stiffer while its margin be softer. These special distribution and composition of the veins mainly account for the distinct behavior of lotus.

Influence of cold rolling and ageing treatment on microstructure and mechanical properties of Ti-30Nb-5Ta-6Zr alloy.

In this study, the relationship between deformation mechanism and rolling reductions was investigated, and the effects of deformation reductions on the microstructure and mechanical properties of the alloys both cold rolled and aged were revealed. It was found that the equiaxed β grains of the Ti-30Nb-5Ta-6Zr alloy have elongated gradually with increasing the deformation reduction. The deformation mechanism of dislocation slipping, deformed twins and SIM α″ phase appeared in the alloy deformed by 23% and 66%. The type of twins of the alloy deformed by 23% and 66% are {112}〈111〉 and {332}〈113〉 respectively. When the reduction was up to 85%, dislocation slipping was the main mode of deformation accompanying with SIM α″ phase occurred. With increasing deformation reduction, the average size of lenticular precipitation α phase decreased gradually. The strength of cold rolled and aged samples increased with increasing deformation reduction, while elastic modulus decreased. Due to the precipitation α phase, the elastic modulus of aged samples was higher than cold rolled.

Low-temperature solution growth of ZnO nanocone/highly oriented nanorod arrays on copper.

Solution-phase approaches to one-dimensional (1D) ZnO nanostructure arrays are appealing because of their good potential for scale-up. Allowing for a wide variety of substrate material compatibility and saving energy, it is very essential to further research the low-temperature growth process of 1D ZnO nanostructure arrays and its detailed growth mechanism. In this study, large-scale misaligned hexagonal ZnO nancone arrays were synthesized on bare copper foil, while large-scale well-aligned, and highly oriented ZnO nanorod arrays were grown on seeded copper foil through a facile solution processing method at normal atmospheric pressure at 35 °C. X-ray diffraction analysis verified the crystalline nature of the ZnO nanocone/nanorods, and transmission electron microscopy further confirmed the single-crystal nature and the preferential growth direction of the ZnO nanocone/nanorods. The room-temperature photoluminescence measurement qualitatively identified the intrinsic point defects in the ZnO nanocones/nanorods. Besides, the detailed growth behavior of ZnO was discussed with and without a ZnO seed layer, which provides useful information to propose the growth mechanism of the nanocone/nanorods in the low-temperature solution. The method developed here can be easily scaled up to fabricate ZnO nanostructures for many important applications in field emission display, gas sensors, and superhydrophobic surfaces.

Direct solution phase fabrication of ZnO nanostructure arrays on copper at near room temperature

Large-scale ZnO nanocone arrays were fabricated by using a [Zn(OH)4]2− solution consisting of Zn(NO3)2·6H2O and KOH on copper foil at near room temperature (~35 °C). The ZnO nanocones showed aligned growth on the downward surface when the copper foil floated in the solution. However, random growth of block-like microcrystals and microflowers composed of nanocones occurred on the upward surface if the foil was placed in the solution. In the [Zn(OH)4]2− solution, the growth of ZnO and Zn(OH)2 was a competitive process, the downward surface and the relatively high growth temperature were beneficial to the formation and growth of ZnO, and the pure and aligned ZnO arrays were obtained on the downward surface at 35 °C. Furthermore, the detailed growth behaviors of the crystals were discussed. We proposed that van der Waals epitaxy and Volmer–Weber growth accompanied by Ostwald ripening controlled the nucleation and growth of ZnO nanocone arrays on the downward surface of the copper foil, while oriented attachment and gravity deposition commanded the morphology on the upward surface in the solution.

Large-scale fabrication of waterborne superamphiphobic coatings for flexible applications

In recent years, there have been great achievements in superhydrophobic coatings. However, there are still some barriers restricting superhydrophobic coatings in practical applications, such as widely used organic solvents and poor oleophobicity. In this study, we proposed a method for fabricating absolutely waterborne superamphiphobic coatings in two steps. Firstly, we synthesized the waterborne SiO2 sol using methyltriethoxysilane, and then the SiO2 sol was modified in an aqueous system with a fluorocarbon surfactant. The results showed that the coating had contact angles of 160°, 153° and 150° and sliding angles of 1°, 4.7° and 6.3° with respect to water, soybean oil and hexadecane. Moreover, the coating could withstand 300 °C heating and immersion in various corrosive solutions for several hours. Furthermore, it is worth mentioning that the waterborne coating showed excellent performances in antifouling, self-cleaning, and damp-proof fields.