Coalescence and counterflow of droplets on needle electrode with negative corona discharge

The coalescence of droplets on the discharge electrode surface in high humidity environments has rarely been studied, which may affect discharge characteristics. Meanwhile, directional transport of droplets is of great significance for many applications ranging from fluidic processing to thermal management. Here, corona discharge in needle-plate electrode is adopted to explore the coalescence rule of droplets attached on the discharge electrode surface in high-humidity environment, and realize the counterflow of droplets. The experimental results show that the amount of coalesced droplets on the needle electrode surface reaches the maximum under -7.5 kV at relative humidity ~ 94% and ambient temperature ~ 20 ℃. When the applied voltage increases from -6 kV to -11 kV, the droplet moves up 2.76 mm in 5 s. The size of attached droplet depends on the balance of coalescence and evaporation. The coalescence is mainly attributed to the dielectrophoretic force caused by the high electric field gradient. The evaporation is related with the ionic wind generated by the corona discharge. As for the counterflow phenomenon of droplet, we speculate that the high concentration gradient of positive ions near the needle electrode provides a driving force for the negatively charged droplets. Meanwhile, the electrons and negative ions below the needle tip offer a repulsive force to the droplet. The shape and moving direction of the droplet attached on the needle surface can be manipulated by changing the voltage applied to the needle electrode, which shows the potential application value in realizing self-cleaning of electrode, liquid lens and so on.

Polymer additive engineering of K2CuBr3 nanocrystalline films to achieve efficient and stable deep-blue emission

Recently, non-toxic alternatives to lead-halide perovskites have been greatly sought after in optoelectronics applications. Deep-blue luminescent material is mainly required for fabricating white light source and expanding the color gamut of full-color displays. However, the synthesis of high-performance lead-free perovskite films with efficient blue emission is still a critical challenge currently, limiting their further practical applications. Here, a novel strategy is reported to prepare non-toxic and deep-blue-emitting K2CuBr3 nanocrystalline films by introducing polymer poly(methyl methacrylate) (PMMA) additives into the anti-solvent. It is found that the PMMA additives could effectively reduce the grain size and improve the crystallinity of K2CuBr3 films, resulting in an enhanced radiative recombination by defect passivation and confinement of excitons in the nanograins. As a result, the PMMA-treated K2CuBr3 films achieve a bright deep-blue light with color coordinates at (0.155, 0.042), and the photoluminescence quantum yield obtained is about 3.3 times that of the pristine sample. Moreover, the treated K2CuBr3 films exhibit a substantially enhanced stability under harsh environmental conditions, maintaining >70% of their initial performances in high humidity environment (50‒70% humidity, 190 h) or under uninterrupted ultraviolet light radiation (254 nm, 3.4 mW/cm2, 150 h). These findings pave a promising strategy for achieving efficient and stable deep-blue metal halide films, showing their potential applications in optoelectronic devices.

Room-Temperature Self-Healing Elastomer based on Van der Waals Forces in Air and under Water

With the development of flexible wearable electronic devices, researches on self-healing conductive materials have become prevalent. However, the self-healing performance of most conductive self-healing materials is commonly achieved by the external stimulus that may cause damage to the equipment. Pparticularly, these self-healing materials may lose the self-healing properties when exposed to a high-humidity environment. Here, we adopted two hydrophobic monomers (2-methoxyethyl acrylate and ethyl methacrylate) to obtain a self-healing elastomer that could display self-healing properties in air or under water though van der Waals forces. The quality and mechanical properties of the elastomer material could keep stable after stored under water for half a month. This elastomer material was capable of self-healing in different environments with self-repair efficiencies more than 50% in deionized water, strong acid solution and strong alkaline solution. The self-repair efficiencies were up to 77% at room temperature(T=25°C) and 64% at low temperature (T=-20°C) in air.

Enhancement of Condensation Heat Transfer, Anti-Frosting and Water Harvesting by Hybrid Wettability Coating

Hydrophilic–hydrophobic hybrid wettability structures, inspired by desert beetles, have been widely designed to enhance the dewdrops’ migration under subcooled or/and high-humidity environment. However, it is still a challenge to regulate the graded distribution of the hydrophilic micro-regions for condensation applications. In this paper, we design a simple spray method to prepare the superamphiphilic–superamphiphobic hybrid wettability coatings by controlling the mass ratio (MR) of superamphiphobic SiO2 nano-powder and superamphiphilic gypsum micro-powder. We compare the macroscopical wettability, condensation heat transfer efficiency, frosting delayed time and water harvesting rate to demonstrate the unique advantage of hybrid wettability structures. The results show that the condensation heat transfer efficiency, frosting delayed time and water harvesting rate can be respectively promoted to about 131.50% [Formula: see text], 134.74% [Formula: see text] and 135.62% [Formula: see text], although their macroscopical wettability will gradually reduce with the MR increase. This work will provide substantial insights into the fabrication of efficient superhydrophilic–superhydrophobic hybrid wettability surfaces for condensation heat transfer, anti-frosting and water harvesting applications.

Performance Degradation of Polymer Solar Cells Measured in High Humidity Environment

Performance degradation is one of the crucial difficulties for the market of organic solar cell (OSC) devices. These deteriorative characteristics can be attributed to many factors, mainly to the chemical reactivity of the device multiple layers with the environment. Here, we investigate the performance of a standard OSC device made of the polymer poly(3-hexylthiophene-2,5-diyl) and the fullerene [6,6]-phenyl-C61-butyric-acid-methyl-ester (P3HT:PCBM) as a photoactive layer in a high humidity environment (53%) within 100 days divided into three periods. The results confirm that the OSC devices’ encapsulations should be completed immediately after the fabrication due to fast chemical degradation of the photoactive layer, which reduces the Jsc by 15% after 40 mins of fabrication. We also found that the FF has been reduced by 17.36% from its initial value after 1152 hours due to a deficiency of the interfacial charge transfer between the multiple layers of the device. Finally, the performance of the device’s decays to zero after 2400 hours.