Dynamics of Droplets Impacting on Aerogel, Liquid Infused, and Liquid-Like Solid Surfaces

Evolution Characteristics and Mechanism of Three-Phase Contact Line of a DNA Microdroplet Impacting and Spreading on a Hydrophilic Horizontal Solid Surface

The phenomena and characteristics of droplets impacting and spreading on a horizontal solid surface are key scientific issues in microfluidic technology and surface physics. The movement regularity and mechanism of the three-phase contact line (TCL) of DNA microdroplets spreading on a hydrophilic PMMA smooth surface without splashing or rebounding are investigated by high-speed camera technology. Some significant results are achieved, for example: based on the changes in droplet morphology, the changes of DNA droplet TCL are divided into eight stages, i.e., expanding, pinning, retracting, repinning, microexpanding, micro-oscillating, stabilizing, and retraction drying, which are helpful to understand the deposition of DNA molecules on the substrate surface. Among them, the TCL moves intensely in the stages of expanding and retracting, respectively, following the cubic function and quadratic function; then, TCL remains virtually unchanged since entering the repinning stage until the stabilizing stage, and DNA molecules are deposited on the surface of PMMA, accumulating to form crystals. Furthermore, the relationship between three correlated damped-like oscillations, i.e., droplet top height (htop), TCL position, and dynamic contact angle (DCA) size, is systematically investigated; the htop oscillates first, then the TCL and DCA oscillate after a delay of 5 ms, and the oscillation period increases sequentially, which is 7.55, 7.90, and 8.40 ms, respectively. Finally, the effects of dynamic characteristics and crystallization of DNA molecules on TCL movement and DCA size are expounded. This research provides detailed experimental data and proposes a theoretical model for understanding the dynamic mechanism of DNA droplet spreading on solid surfaces and has been helpful for designing DNA chips and developing micro-/nano-fluidic sensors.

Multifunctional aluminum alloy slippery liquid-infused surface with porous and boehmite nanoflower structure

The depletion of lubricants in (slippery liquid-infused porous surfaces) SLIPS poses a significant challenge to their long-term functionality. While line-shaped rough structures can mitigate lubricant loss to some extent, they often fail to provide the stability required for sustained performance. In this study, we present a novel porous nanoflower aluminum alloy slippery liquid-infused surface (P-NF-AA SLIPS), which integrates a porous framework with a rough nanoflower structure. This synergistic design offers dual benefits of enhanced oil storage and retention, leading to superior stability and durability. Remarkably, after centrifugation at 7000 rpm, the silicone oil retention of P-NF-AA SLIPS remains between 70-75 % of its pre-centrifugation mass. The surface demonstrates excellent adaptability to prolonged use under varying temperatures and pH levels. In fog collection, P-NF-AA SLIPS demonstrates rapid water droplet capture and detachment, achieving a fog collection efficiency of approximately 0.4 g·min-1·cm-2 within 10 min-an improvement of 185.7 % and 68.4 % over the original aluminum alloy (OAA) and superhydrophobic aluminum alloy (SHB-AA), respectively. Additionally, P-NF-AA SLIPS delays icing by 560 s at -15 °C and 231 s at -30 °C, offering remarkable anti-icing and de-icing performance. Furthermore, it demonstrates excellent self-cleaning properties against contaminants such as sand, coffee powder, and dye solutions. P-NF-AA SLIPS has advanced research on SLIPS and supports the application of biomimetic slippery surfaces in fields such as self-cleaning materials, anti-icing and anti-frost coatings, droplet control and transport, as well as biomedical applications.

Emitted droplets and aerosols and their transmission when drying hands under an air-jet dryer

When drying hands with a high-speed air jet dryer, the jet impingement on hands can quickly atomize the remnant water on the hand skins into droplets and aerosols. Emission of droplets and liquid aerosols, their spatial transport and the possible inhaling exposure to the hand dryer user remain unclear. This investigation measured the jet flows from a downward air jet dryer, by the particle image velocimetry (PIV), the helium bubble trajectory analysis, and an ultrasonic anemometer. Emission of the droplets when turning over the hands, the droplet spatial motion, and their deposition on human body were photographed by a high speed camera. Concentrations of the liquid aerosols were monitored and the total emitted aerosol numbers and size spectrum were analyzed. The possible inhalation exposure to the emitted liquid aerosols was examined. It is found that number of droplets in size of 0.1 to 0.6 mm can deposit on the mouth and nose and the surrounding face. A typical hand drying process may emit approximately 105 liquid aerosols, of which 93 % are in the submicron size. A hand dryer user may inhale thousands of the emitted liquid aerosols if drying hands without wearing face mask.

Recent progress in understanding the anti-icing behavior of materials

Despite the significant progress in fundamental research in the physics of atmospheric icing or the revolutionary changes in modern materials and coatings achieved due to the recent development of nanotechnology and synthetic chemistry, the problem of reliable protection against atmospheric icing remains a hot topic of surface science. In this paper, we present a brief analysis of the mechanisms of anti-icing behavior that attracted the greatest interest of the scientific community and approaches which realize these mechanisms. We also note the strengths and weaknesses of such approaches and discuss future studies and prospects for the practical application of developed coatings.