The ability of superhydrophobic surfaces to stay dry, self-clean and avoid biofouling is attractive for applications in biotechnology, medicine and heat transfer 1-10 . It requires that water droplets placed on superhydrophobic surfaces have large apparent contact angles (θ* > 150°) and low roll-off angles (θroll-off < 10°), realized with surfaces having low-surface-energy chemistry as well as micro-or nanoscale surface roughness that minimizes liquid-solid contact 11-17 . But rough surfaces where liquid contacts only a small
Space cooling and heating currently result in huge amounts of energy consumption and various environmental problems. Herein, a switching strategy is described for efficient energy‐saving cooling and heating based on the dynamic cavitation of silicone coatings that can be reversibly and continuously tuned from a highly porous state to a transparent solid. In the porous state, the coatings can achieve efficient solar reflection (93%) and long‐wave infrared emission (94%) to induce a subambient temperature drop of about 5 °C in hot weather (≈35 °C). In the transparent solid state, the coatings allow active sunlight permeation (95%) to induce solar heating to raise the ambient temperature from 10 to 28 °C in cold weather. The coatings are made from commercially available, cheap materials via a facile, environmentally friendly method, and are durable, reversible, and patternable. They can be applied immediately to various existed objects including rigid substrates.
The World Health Organization declared the novel coronavirus (COVID-19) outbreak as a pandemic on March 12, 2020. Within 3-1/2 months since outbreak in December 2019, over 1.3 million people have been infected across 206 countries with over 70,000 deaths. COVID-19 has a size of 60-140nm with mean size of the nano-aerosols, 100nm. The virus can be airborne by attaching to human secretion (fine particles, nasal/saliva droplets) of infected person or suspended fine particulates in air. While NIOSH has standardized N95 and N98 at 300nm, to-date there is no filter standards, nor special filter technologies, tailored for capturing airborne viruses and 100nm nano-aerosols. The latter also are present in high number concentration in atmospheric pollutants. This study addresses developing novel charged PVDF nanofiber filter technology to effectively capture the deadly airborne coronavirus with our target set at 100nm (nano-aerosol), and not 300nm.The virus and its attached particle were simulated by sodium chloride aerosols, 50-500nm, generated from sub-micron aerosol generator. PVDF nanofibers were produced with fiber diameters 84, 191, 349 and 525nm with excellent morphology. The fibers were subsequently charged by corona discharge.The amounts of charged fibers in a filter were increased to achieve high efficiency of 90% for the virus filter but the electrical interference between neighbouring fibers resulted in progressively marginal increase in efficiency and concurrently much higher pressure drop across the filter. The quality factor which measured the efficiency-to-pressure-drop kept decreasing. By redistributing the fibers in the filter into several modules, each separated by a permeable scrim material, the electrical interference was reduced, if not fully mitigated.Also, the additional scrim materials introduced macropores into the filter that further reduced the airflow resistance. With this approach, the quality factor can maintain relatively constant with increasing fiber amounts to achieve high filter efficiency. The optimal amounts of fiber in each module depended on the diameter of fibers in the module. Small fiber diameter that has already high performance required small amount of fibers per module. In contrast, large diameter fiber required more amounts of fiber per module to compensate for the poorer performance without incurring higher pressure drop. This approach was applied to develop four new nanofiber filters tailored for capturing 100nm airborne COVID-19 to achieve over 90% efficiency with pressure drop below 30Pa (3.1mm water). One filter developed meeting the 90% efficiency has ultralow pressure drop of only 18Pa (1.9mm water) while another filter meeting the 30Pa limit has high efficiency reaching 94%. These optimized filters based on rigorous engineering approach provide the badly needed technology for protecting the general public from the deadly airborne COVID-19 and other viruses, and nano-aerosols from air pollution which lead to chronic diseases.
Earthworms are able to pass through sticky soil without inducing stains through a self-forming thick lubricating layer on their rough skins. To mimic this earthworm-like lubricating capability, an attempt to create a textured structure on the surface of liquid-releasable polymer coatings by a "breath figure" process is described herein. The resulting coatings exhibit fast and site-specific release behavior under external triggers such as solid-based friction. The released oil is then stabilized by the surface texture to form thick lubricating layers, reducing friction and enhancing wear resistance. Moreover, the coatings also exhibit excellent antifouling property in a sticky soil environment. Because the lubricating layer can be regenerated after consumption, the potential of this self-replenished lubricating mechanism in preparing friction-reduction, antiwear, and antifouling coatings used in solid-based environments is therefore envisioned.
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