Mechanical properties of nanocrystalline materials

Design, and Applications Shutao Wang,†,‡ Kesong Liu, Xi Yao, and Lei Jiang*,†,‡,§ †Laboratory of Bio-inspired Smart Interface Science, Technical Institute of Physics and Chemistry, and ‡Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry and Environment, BeiHang University, Beijing 100191, People’s Republic of China Department of Biomedical Sciences, City University of Hong Kong, Hong Kong P6903, People’s Republic of China

Bioinspired Surfaces with Superwettability: New Insight on Theory, Design, and Applications

CuO nanostructures: Synthesis, characterization, growth mechanisms, fundamental properties, and applications

Fogging occurs when moisture condensation takes the form of accumulated droplets with diameters larger than 190 nm or half of the shortest wavelength (380 nm) of visible light. This problem may be effectively addressed by changing the affinity of a material’s surface for water, which can be accomplished via two approaches: i) the superhydrophilic approach, with a water contact angle (CA) less than 5°, and ii) the superhydrophobic approach, with a water CA greater than 150°, and extremely low CA hysteresis. To date, all techniques reported belong to the former category, as they are intended for applications in optical transparent coatings. A well-known example is the use of photocatalytic TiO2 nanoparticle coatings that become superhydrophilic under UV irradiation. Very recently, a capillary effect was skillfully adopted to achieve superhydrophilic properties by constructing 3D nanoporous structures from layer-by-layer assembled nanoparticles. The key to these two “wet”-style antifogging strategies is for micrometer-sized fog drops to rapidly spread into a uniform thin film, which can prevent light scattering and reflection from nucleated droplets. Optical transparency is not an intrinsic property of antifogging coatings even though recently developed antifogging coatings are almost transparent, and the transparency could be achieved by further tuning the nanoparticle size and film thickness. To our knowledge, the antifogging coatings may also be applied to many fields that do not require optical transparency, including, for example, paints for inhibiting swelling and peeling issues and metal surfaces for preventing corrosion. These types of issues, which are caused by adsorption of moisture, are hard to solve by the superhydrophilic approach because of its inherently “wet” nature. Thus, a “dry”-style antifogging strategy, which consists of a novel superhydrophobic technique that can prevent moisture or microscale fog drops from nucleating on a surface, is desired. Recent bionic researches have revealed that the self-cleaning ability of lotus leaves and the striking ability of a water-strider’s legs to walk on water can be attributed to the ideal superhydrophobicity of their surfaces, induced by special microand nanostructures. To date, the biomimetic fabrication of superhydrophobic microand/or nanostructures has attracted considerable interest, and these types of materials can be used for such applications as self-cleaning coatings and stain-resistant textiles. Although a superhydrophobic technique inspired by lotus leaves is expected to be able to solve such fogging problems because the water droplets can not remain on the surface, there are no reports of such antifogging coatings. Very recently, researchers from General Motors have reported that the surfaces of lotus leaves become wet with moisture because the size of the fog drops are at the microscale—so small that they can be easily trapped in the interspaces among micropapillae. Thus, lotuslike surface microstructures are unsuitable for superhydrophobic antifogging coatings, and a new inspiration from nature is desired for solving this problem. In this communication, we report a novel, biological, superhydrophobic antifogging strategy. It was found that the compound eyes of the mosquito C. pipiens possess ideal superhydrophobic properties that provide an effective protective mechanism for maintaining clear vision in a humid habitat. Our research indicates that this unique property is attributed to the smart design of elaborate microand nanostructures: hexagonally non-close-packed (ncp) nipples at the nanoscale prevent microscale fog drops from condensing on the ommatidia surface, and hexagonally close-packed (hcp) ommatidia at the microscale could efficiently prevent fog drops from being trapped in the voids between the ommatidia. We also fabricated artificial compound eyes by using soft lithography and investigated the effects of microand nanostructures on the surface hydrophobicity. These findings could be used to develop novel superhydrophobic antifogging coatings in the near future. It is known that mosquitoes possess excellent vision, which they exploit to locate various resources such as mates, hosts, and resting sites in a watery and dim habitat. To better understand such remarkable abilities, we first investigated the interaction between moisture and the eye surface. An ultrasonic humidifier was used to regulate the relative humidity of the atmosphere and mimic a mist composed of numerous tiny water droplets with diameters less than 10 lm. As the fog was C O M M U N IC A IO N

The dry-style antifogging properties of mosquito compound eyes and artificial analogues prepared by soft lithography: a superhydrophobic state with high adhesive force

In a previous communication, we reported a new method of synthesis of stable metallic copper nanoparticles (Cu-NPs), which had high potency for bacterial cell filamentation and cell killing. The present study deals with the mechanism of filament formation and antibacterial roles of Cu-NPs in E. coli cells. Our results demonstrate that NP-mediated dissipation of cell membrane potential was the probable reason for the formation of cell filaments. On the other hand, Cu-NPs were found to cause multiple toxic effects such as generation of reactive oxygen species, lipid peroxidation, protein oxidation and DNA degradation in E. coli cells. In vitro interaction between plasmid pUC19 DNA and Cu-NPs showed that the degradation of DNA was highly inhibited in the presence of the divalent metal ion chelator EDTA, which indicated a positive role of Cu(2+) ions in the degradation process. Moreover, the fast destabilization, i.e. the reduction in size, of NPs in the presence of EDTA led us to propose that the nascent Cu ions liberated from the NP surface were responsible for higher reactivity of the Cu-NPs than the equivalent amount of its precursor CuCl2; the nascent ions were generated from the oxidation of metallic NPs when they were in the vicinity of agents, namely cells, biomolecules or medium components, to be reduced simultaneously.

https://iopscience.iop.org/article/10.1088/0957-4484/25/13/135101/pdf

Mechanism of antibacterial activity of copper nanoparticles.

Copper nanoparticles protected by self-assembled monolayers of decanethiol have been prepared by the controlled reduction of aqueous copper salts using the modified Brust synthesis. For comparison, the nanoparticles are synthesized on different concentration of cetyltrimethylammonium bromide (CTAB). TEM, XPS, XRD, IR have been employed to investigate the structure and formation of these nanoparticles. It was found that CTAB plays a critical role in controlling stability and ease to formation 3D SAMs during synthesis.

The use of CTAB to control the size of copper nanoparticles and the concentration of alkylthiols on their surfaces

"Structural superlubricity" is an important fundamental phenomenon in modern tribology that is expected to greatly diminish friction in mechanical engineering, but now is limited to achieve only at nanoscale and microscale in experiment. A novel principle for broadening the structural superlubricating state based on numberless micro-contact into macroscale superlubricity is demonstrated. The topography of micro-asperities on engineering steel substrates is elaborately constructed to divide the macroscale surface contact into microscale point contacts. Then at each contact point, special measures such as pre-running-in period and coating heterogeneous covalent/ionic or ionic/ionic nanocomposite of 2D materials are devised to manipulate the interfacial ordered layer-by-layer state, weak chemical interaction, and incommensurate configuration, thereby satisfying the prerequisites responsible for structural superlubricity. Finally, the robust superlubricating states on engineering steel-steel macroscale contact pairs are achieved with significantly reduced friction coefficient in 10-3 magnitude, extra-long antiwear life (more than 1.0 × 106 laps), and good universality to wide range of materials and loads, which can be of significance for the industrialization of "structural superlubricity."

Toward Robust Macroscale Superlubricity on Engineering Steel Substrate

Cavitation erosion of several oxy-fuel sprayed coatings tested in deionized water and artificial seawater

Conventional and nanostructured WC–12%Co coatings were deposited on 1Cr18Ni9Ti stainless steel substrate using air plasma spraying. The hardness of the coatings was measured, while their friction and wear behavior sliding against Si3N4 at room temperature and elevated temperatures up to 400 °C was comparatively studied. The microstructures and worn surface morphologies of the coatings were comparatively analyzed as well by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDXA). It was found that the as-sprayed WC–12%Co coatings were composed of WC as the major phase and W2C, WC1−x, and W3Co3C as the minor phases. The plasma sprayed nanostructured WC–12%Co coating had much higher hardness and refined microstructures than the conventional WC–12%Co coating. This largely accounted for the better wear resistance of the nanostructured WC–12%Co coating than the conventional coating. Besides, the two types of WC–12%Co coatings showed minor differences in friction coefficients, though the nanostructured WC–12%Co coating roughly had slightly smaller friction coefficient than the conventional coating under the same sliding condition. Moreover, both the conventional and nanostructured WC–12%Co coatings recorded gradually increased wear rate with increasing temperature, and the nanostructured coating was less sensitive to the temperature rise in terms of the wear resistance. The worn surfaces of the conventional WC–12%Co coating at different sliding conditions showed more severe adhesion, microfracture, and peeling as compared to the nanostructured WC–12%Co coating, which well conformed to the corresponding wear resistance of the two types of coatings. The nanostructured WC–12%Co coating with a wear rate as small as 1.01 × 10−7 mm3/Nm at 400 °C could be promising candidate coating for the surface-modification of some sliding components subject to harsh working conditions involving elevated temperature and corrosive medium.

Huidi Zhou

Papers

The use of CTAB to control the size of copper nanoparticles and the concentration of alkylthiols on their surfaces

Toward Robust Macroscale Superlubricity on Engineering Steel Substrate

Cavitation erosion of several oxy-fuel sprayed coatings tested in deionized water and artificial seawater

Comparative study of the friction and wear behavior of plasma sprayed conventional and nanostructured WC–12%Co coatings on stainless steel

Phase composition and tribological properties of Ti–Al coatings produced on pure Ti by laser cladding