Rapid preparation and antimicrobial activity of polyurea coatings with RE-Doped nano-ZnO.

The recent COVID-19 virus has led to a rising interest in antimicrobial and antiviral coatings for frequently touched surfaces in public and healthcare settings. Such coatings may have the ability to kill a variety of microorganisms and bio-structures and reduce the risk of virus transmission. This paper proposes an extremely rapid method to introduce rare-earth doping nano-ZnO in polyamines for the preparation of the anti-microbial polyurea coatings. The nano-ZnO is prepared by wet chemical method, and the RE-doped nano-ZnO was obtained by mixing nano ZnO and RE-dopants with an appropriate amount of nitric acid. This rapidly fabricated polyurea coating can effectively reduce bacteria from enriching on the surface. Comparing with pure nano-ZnO group, all the polyurea coatings with four different rare-earth elements (La, Ce, Pr and Gd) doped nano-ZnO. The La-doped nano-ZnO formula group indicates the highest bactericidal rate over 85% to Escherichia coli (E. coli) and Pseudomonas aeruginosa (Pseudomonas). Followed by Ce/ZnO, the bactericidal rate may still remain as high as 83% at room temperature after 25-min UV-exposure. It is believed that the RE-doping process may greatly improve the photocatalytic response to UV light as well as environmental temperature due to its thermal catalytic enhancement. Through the surface characterizations and bioassays, the coatings have a durably high bactericidal rate even after repeated usage. As polyurea coating itself has high mechanical strength and adhesive force with most substrate materials without peel-off found, this rapid preparation method will also provide good prospects in practical applications.

Effect of Nano-Titanium Dioxide Contained in Titania-Polyurea Coating on Marina Biofouling and Drag Reduction.

Marine structures often suffer from biofouling, which may lead to macrofouling by marine animals like marine worms and barnacles, weighing down the structures and increasing the drag. This paper analyses the effect of the newly fabricated biological anti-adhesion Titania-Polyurea spray coating, which can effectively reduce biofouling from enriching on the surface. Through the surface characterization, bioassays and micro-channel drag-reduction test, the antibacterial effect caused by the nano-titanium dioxide is systematically studied. Compared to the different weight percentages of nano-TiO2 in the coating system, the photocatalytic activity, riblet surface structure and hydrophobic wettability are supposed to be the key factors to reduce the flow resistance at a drag reduction rate of 3.0% and further enhance the anti-biofouling performance under dark conditions.

Effect of Surface Mechanical Treatments on the Microstructure-Property-Performance of Engineering Alloys.

Fatigue is a dominant failure mechanism of several engineering components. One technique for increasing the fatigue life is by inducing surface residual stress to inhibit crack initiation. In this review, a microstructural study under various bulk (such as severe plastic deformation) and surface mechanical treatments is detailed. The effect of individual microstructural feature, residual stress, and strain hardening on mechanical properties and fatigue crack mechanisms are discussed in detail with a focus on nickel-based superalloys. Attention is given to the gradient microstructure and interface boundary behavior for the mechanical performance. It is recommended that hybrid processes, such as shot peening (SP) followed by deep cold rolling (DCR), could enhance fatigue life. The technical and scientific understanding of microstructural features delineated here could be useful for developing materials for fatigue performance.

Failure Behavior of Unidirectional Composites under Compression Loading: Effect of Fiber Waviness.

The key objective of this work is to highlight the effect of manufacturing-induced fiber waviness defects on the compressive failure of glass fiber-reinforced unidirectional specimens. For this purpose, in-plane, through-thickness waviness defects (with different waviness severities) are induced during the manufacturing of the laminate. Numerical and experimental results show that the compressive strength of the composites decreases as the severity of the waviness defects increases. A reduction of up to 75% is noted with a wave severity of 0.075. Optical and scanning electron microscopy observations of the failed specimens reveal that kink-bands are created in the wavy regions and lead to failure.