ABSTRACT
Superhydrophobic surfaces demonstrate excellent anti-icing performance under static conditions. However, they show a marked decrease in icing time under real flight conditions. Here we develop an anti-icing strategy using ubiquitous wind field to improve the anti-icing efficiency of superhydrophobic surfaces during flight. We find that the icing mass on hierarchical superhydrophobic surface with a microstructure angle of 30° is at least 40% lower than that on the conventional superhydrophobic plate, which is attributed to the combined effects of microdroplet flow upwelling induced by interfacial airflow and microdroplet ejection driven by superhydrophobic characteristic. Meanwhile, the disordered arrangement of water molecules induced by the specific 30° angle also raises the energy barriers required for nucleation, resulting in an inhibition of the nucleation process. This strategy of microdroplet movement manipulation induced by interfacial airflow is expected to break through the anti-icing limitation of conventional superhydrophobic materials in service conditions and can further reduce the risk of icing on the aircraft surface.
ABSTRACT
Effect mechanisms of the undercooling degree and the surface configuration on the ice growth characteristics were revealed under micro-droplets icing conditions. Preferential ice crystals appear firstly on the surfaces due to the randomness of icing, and obtain growth advantages to form protruding structures. Protruding structures block the incoming droplets from contacting the substrates, causing voids around the structures. The undercooling degree mainly affects the density and the growth rate of preferential ice crystals. With the increase of undercooling degree, the preferential ice crystals have higher density and growth rate, resulting in stronger growth advantage and higher porosity. The surface configuration affects the growth mode, and the ice layer grows with uniform mode, spreading mode and structure-induced mode on the aluminum, smooth Polytetrafluoroethylene (PTFE) and rough PTFE surface respectively, causing the needle-like, ridge-like and cluster-like ice crystals. The rough structures effectively improve the porosity of the ice layer, which is beneficial for optimizing the icephobic property of the materials. This paper provides important theoretical guidance for the design of subsequent icephobic materials.
ABSTRACT
The controllable spontaneous transport of water droplets on solid surfaces has a broad application background in daily life. Herein, a patterned surface with two different non-wetting characteristics was developed to control the droplet transport behavior. Consequently, the patterned surface exhibited great water-repellant properties in the superhydrophobic region, and the water contact angle reached 160° ± 0.2°. Meanwhile, the water contact angle on the wedge-shaped hydrophilic region dropped to 22° after UV irradiation treatment. On this basis, the maximum transport distance of water droplets could be observed on the sample surface with a small wedge angle of 5° (10.62 mm), and the maximum average transport velocity of droplets was obtained on the sample surface with a large wedge angle of 10° (218.01 mm/s). In terms of spontaneous droplet transport on an inclined surface (4°), both the 8 µL droplet and 50 µL droplet could move upward against gravity, which showed that the sample surface possessed an obvious driving force for droplet transport. Surface non-wetting gradient and the wedge-shaped pattern provided unbalanced surface tension to produce the driving forces in the process of droplet transport, and the Laplace pressure as well is produced inside the water droplet during this process. This work provides a new strategy to develop a patterned superhydrophobic surface for droplet transport.
ABSTRACT
The relation between polymer molecular chains arrangement and ice adhesion was studied at the molecular scale, and the energy states of water molecules on the poly(tetrafluoroethylene) surface were analyzed to explain the energy essence of ice adhesion. The ice adhesion on crystalline poly(tetrafluoroethylene) displayed a clear anisotropy phenomenon. Further research proved that the energy states of water molecules along the vertical direction of the molecular chains fluctuated regularly, and the water molecules in gaps between molecular chains were in the energy troughs, leading to the formation of energy traps. Water molecules needed more energy from outside to escape the energy traps, causing additional resistance to the ice movement and obvious increase of ice adhesion. Therefore, ice adhesion was closely related to the distribution of energy traps in the direction of ice removing, which mainly depended on the possibility of molecular chains perpendicularly arranged in the direction of ice removing.
ABSTRACT
The design of electrocatalysts with lower overpotential is of great significance for water splitting. Herein, cobalt hydroxide carbonate (CCH) has been used as a model to demonstrate the boost of its oxygen evolution reaction (OER) activity by atomic doping of W6+ (W-CCH). The 5 at % W doping reduced the OER overpotential of CCH by 95.3 mV at 15 mA cm-2, and increased the current density by 2.8 times at 1.65 V. 5%W-PCCH || 5%W-CCH-based electrolyzer only required a potential of 1.65 V to afford 10 mA cm-2 for full water splitting. The W6+ in CCH are active sites for O2- adsorption and induced an incesaed electron density near the Fermi level, which facilitates the charge transfer during electrocatalysis. The W6+ doping has been validated as an efficient booster for transition-metal carbonate hydroxides-based electrocatalysts, which has half or more than half-filled d-bands.
ABSTRACT
OBJECTIVE: To observe the effects of Coptis Chinensis on vasoconstrictive activity of isolated thoracic aorta rings of normoxic and chronic intermittent hypobaric hypoxic (CIHH) rats, and to investigate the underlying mechanisms. METHODS: Young male Sprague-Dawley rats were randomly divided into normoxic group and CIHH group: the fonnrmer were not given any special treatment; the latter were exposed to hypoxia in a hypobaric chamber simulating 5000 m altitude (PB = 404 mmHg, PO2 = 84 mmHg, 11.1% O2), 6 hours daily for 28 days. The isolated thoracic aorta rings of rats were prepared and perfused in thermostat, and the effects of Coptis on vasoconstrictive activity of aorta rings were recorded, the mechanisms were investigated simultaneouly. RESULTS: Coptis Chinensis significantly decreased NE and KC-induced vasoconstriction of normoxic and CIHH rats' isolated aortic rings, but the inhibitive effects had no obvious discrepancy between the two groups. The contractive amplitude had no marked change after the removal of endothelium. When calculated by Logit Loglinear analysis, IC50 of NE and KCl-induced contractive amplitude in normoxic group were respectively 2.99 g/L and 6.14 g/L, while they were 3.45 g/L and 5.81 g/L in CIHH group. The inhibitive effect of Coptis on vasoconstrictive activity of both groups could be partly decreased by Glibenclamide and nitro-L-arginine methyl ester; Indomethacin suppressed the effect on normoxic group as well. Also Coptis significantly inhibited NE-induced both intracellular and extracellular calciumion-depended vasoconstriction. CONCLUSION: Coptis Chinensis obviously relaxes isolated thoracic aorta rings of normoxic and CIHH rats, but the effects are endothelium-independent and have no marked discrepancy between the two groups. The mechanisms of the effects may be related to the opening of ATP-sensitive K+ channel, raise of nitric oxide concentration in both groups, and the increasing of PGI2 in normoxic group. Besides, Coptis may inhibit sarcoplasmic reticulum releasing Ca2+ and decrease the inflow of extracellular Ca2+ via cell membrane.
