Surface Of Water Droplets Research Articles

Development of the mathematical model of heat and mass transfer for researching the processes of evaporation of inhomogeneous water droplets

On the basis of experimental date the heat and mass transfer models are developed in ANSYS Fluent software package for researching the processes of evaporation of inhomogeneous water droplets. The influence of the temperature of the gases (550-850 K) on the evaporation of inhomogeneous water droplets is estimated. Times of complete liquid evaporation from free surface of inhomogeneous water droplets and explosive vaporization of water droplets at different gas temperatures are established.

Development of hydrophobic and optically transparent monolithic silica aerogels for window panel applications

In the present paper, highly transparent, monolithic and hydrophobic silica aerogel monoliths were prepared by using tetraethoxysilane (TEOS) as precursor and methyltriethoxysilane (MTES) as co-precursor with different MTES/TEOS molar ratios (M) by two-step acid–base catalyzed sol–gel process followed by supercritical alcohol drying. The molar ratio of TEOS, ethanol (EtOH), water (0.001 M oxalic acid catalyst) and ammonium hydroxide (1 M NH4OH) was kept constant at 1:5:3.5:3.5 respectively, while the molar ratio of MTES/TEOS (M) was varied from 0 to 0.75. It has been observed that as the M value increases, the gelation time increases. It has been found that lower (0.25) M values resulted in highly transparent (optical transmission >90 % for a 10 mm thick sample at 700 nm wavelength) and negligible volume shrinkage ( 10 % volume shrinkage but excellent hydrophobicity. A good compromise of acceptable optical transmittance (~87 % optical transmission at 700 nm wavelength for a 10 mm thick sample) with negligible volume shrinkage (6 %) were obtained at M = 0.50. The hydrophobicity of the aerogels was tested by measuring the contact angle between a water droplet and silica aerogel surface. The hydrophobicity was confirmed by Fourier transform infra-red spectroscopy and contact angle measurements. the aerogels have been characterized by percentage of volume shrinkage, optical transmittance, scanning electron microscopy, thermal conductivity measurements and thermogravimetric analysis and differential thermal analysis.

Surface modification of bacterial cellulose membrane by oxygen plasma treatment

Abstract In order to fabricate cellulose membranes for filtration in various applications, a study on changes in properties of bacterial cellulose by treatments with oxygen plasma has been carried out. Bacterial cellulose was produced from Acetobacter xylinum as a thin membrane of 0.01 μm pore size with hydrophilic property. Plasma treatments of the membranes were conducted under the variation of pressure, time exposure, and net power dissipation from the RF source using oxygen gas. At 250 kPa, the averaged water flux of the membranes was only 5 Lm − 2 h − 1 and was reduced further after plasma treatment, regardless of changes in obtained water droplet surface contact angle. ATR-FTIR results showed changes in functional groups of this biomaterial after treatment. The peak at 713 cm − 1 for O–H out-of-plane bending increased remarkably. An enlargement of peak at 3340 cm − 1 indicated the higher number of water molecules surrounding the membrane resulting in a change to a more hydrophilic membrane which is in good agreement with the result from surface contact angle measurement.

PH-responsive Liquid Marbles Prepared Using Fluorinated Fatty Acid

pH-responsive “liquid marbles” can be prepared by adsorption of a hydrophobic fluorinated fatty acid powder, 2H,2H,3H,3H-heptadecafluoroundecanoic acid (HFUA) onto the surface of water droplet. The...

Flattened-Top Domical Water Drops Formed through Self-Organization of Hydrophobin Membranes: A Structural and Mechanistic Study Using Atomic Force Microscopy

The Trichoderma reesei hydrophobin, HFBI, is a unique structural protein. This protein forms membranes by self-organization at air/water or water/solid interfaces. When HFBI forms a membrane at an air/water interface, the top of the water droplet is flattened. The mechanism underlying this phenomenon has not been explored. In this study, this unique phenomenon has been investigated. Self-organized HFBI membranes form a hexagonal structured membrane on the surface of water droplets; the structure was confirmed by atomic force microscopy (AFM) measurement. Assembled hexagons can form a planar sheet or a tube. Self-organized HFBI membranes on water droplets form a sheet with an array of hexagonal structures or a honeycomb structure. This membrane, with its arrayed hexagonal structures, has very high buckling strength. We hypothesized that the high buckling strength is the reason that water droplets containing HFBI form flattened domes. To test this hypothesis, the strength of the self-organized HFBI membranes was analyzed using AFM. The buckling strength of HFBI membranes was measured to be 66.9 mN/m. In contrast, the surface tension of water droplets containing dissolved HFBI is 42 mN/m. Thus, the buckling strength of a self-organized HFBI membrane is higher than the surface tension of water containing dissolved HFBI. This mechanistic study clarifies why the water droplets formed by self-organized HFBI membranes have a flattened top.

역전기습윤현상을 이용한 소형 에너지 수확장치

In this study, we attempted to harvest energy using water droplet based on Reverse Electro Wetting On Dielectric (REWOD) phenomenon between water droplet and dielectric surface without external bias. REWOD device can be fabricated via simple coating process, which is highly economic and easy. We believe that our system is well-suited for IoT(Internet of Things) embedded electronics that require low but consistent electricity. Moreover, our device can be integrated with window to generate electricity upon raindrops.

Oscillations of a water droplet separated from the connection

The calculation method which makes it possible to predict the behavior of large- and small-scale capillary deformations on the water droplet surface after separation is presented. The calculation scheme is based on the Rayleigh solution for the oscillations of an ideal incompressible fluid droplet and makes it possible to obtain the results which differ from the experimental data by no more than 5%.

Response of Calcium Carbonate Nanoparticles in Hydrophobic Solvent to Pressure, Temperature, and Water

Molecular dynamics simulations of surfactant-stabilized calcium carbonate, CaCO3, nanoparticles in hydrophobic solvent have been carried out to characterize their response to changes in temperature (T) and pressure (P) and also their interaction with trace water and water droplets. The response to increasing temperature and pressure is sensitive to the type of model surfactant, with the sulfonate-stabilized particle, which is the most spherical, showing a weak temperature–pressure dependence, while the sulfurized alkyl phenol and salicylate-stabilized particles distort into a more spherical shape with increasing temperature and pressure. The atom–atom radial distribution functions of the core ions reveal consolidation of the calcium carbonate structure with increasing temperature and pressure. The simulations show that the nanoparticles adsorb onto the surface of water droplets through a water bridge transitional mechanism, in agreement with evidence from experimental studies. In the case of the sulfonate...

Partial discharge inception electric field strength of water droplets on polymeric insulating surfaces

Water droplets are formed on the surface of polymeric insulators under wet conditions, which enhance the electric field especially in close vicinity of the contact line between air, water droplet and insulator surface. It is experimentally found that the maximum allowable E-field strength tangential to a polymeric insulating surface in presence of a single water droplet on the flat surface with wettability class 1 is between 6 and 7.5 kV/cm (peak). Some important parameters that have an influence on PD inception are experimentally investigated to find more reliable results. A simple prediction method of partial discharge inception E-field strength of a single water droplet on polymeric insulating surfaces based on the streamer criterion for inception is also proposed and discussed. The investigated PD inception E-fields in this contribution can be used for prediction of partial discharge inception voltage of polymeric insulators under wet conditions.

Factors controlling hydrate film growth at water/oil interfaces

The methane hydrate film growth kinetics on the surface of water droplets suspended in n-octane was investigated. When the water droplet was suspended in n-octane unsaturated with methane, the hydrate formation behavior on its surface showed a hydrate curtain caused by the continuous forming, moving, and dissociating of hydrate crystals. When n-octane was saturated with methane, the lateral growth rates of the hydrate film were measured under different pressures. The mass transfer of methane molecules near the film front was suggested as the control step of lateral growth. For hydrate film growth in thickness, massive apophyses occurred and developed in the outer surface of the hydrate film, indicating an outward water transfer through the film. The sinking of the hydrate film caused by leaking of the inner water was observed. These two phenomena indicated the contribution of the outward growth of water through the hydrate film in thickening growth.

Rapid Formation of Transparent Superhydrophobic Film on Glasses by He/CH4/C4F8Plasma Deposition at Atmospheric Pressure

A transparent superhydrophobic surface on glass is prepared by a rapid single-step method using a He, CH4, C4F8 mixture plasma at atmospheric pressure. Water droplet contact angles and surface properties are investigated to analyze both chemical and physical characteristics of the plasma treated surfaces. As the C4F8 gas flow rate is increased in the He/CH4 plasma, both advancing, and receding water contact angles are increased, while UV-visible transmittance is degraded. By optimizing the gas mixture ratio, we find rapid deposition conditions for superhydrophobic formation without losing the visible to near-infrared transparency of the glass. The chemical and physical mechanism responsible for hydrophobicity is also discussed through the investigation of chemical composition and surface morphology.

Single Mobile Micro Droplet-Particle Pairs Spatially Captured by Macro Host Droplets on a Superhydrophobic Surface

In this preliminary study, we demonstrate how small single water droplets can be spatially captured on the surface of individual micron sized hydrophobic coated particles (C18) which adhere to the surface of a nonmobile larger host water droplet resting on a superhydrophobic surface. The formation of the larger droplet, particle adhesion to that droplet, and smaller droplet formation on the particle all take place spontaneously from condensation conditions. These micro droplet-particle pairs are confined to the surface (liquid-air interface) of the larger host droplet; however, they are free to engage with external forces to promote mobility. This response may find applications for particle pair transport on liquid surfaces. We also demonstrate that droplets can be captured or removed from the larger droplet surface via a self-propulsion mechanism.

Spreading behavior of a distilled water droplet on a superhydrophobic surface

The investigation of dynamic contact angle between distilled water droplet and superhydrophobic surface was conducted experimentally. To obtain the values of contact angle during spreading, shadow method was implemented. We used Schlieren method to control the droplet symmetry. The droplet was formed on the surface by syringe pump using nontraditional bottom-up methodology. The drop growth rate was varied by the syringe pump from 0.005 ml/s to 0.32 ml/s. DCA versus drop volume was obtained for different values of the drop growth rate. Some features of spreading on superhydrophobic surface were pointed out. Interestingly, that the dynamic contact angle increases during all stages previously selected for copper substrates (1 – droplet formation; 2 – spreading; 3 – formation of the equilibrium contact angle). However, at the droplet growth rate 0.005ml/s we found decrease in the contact angle. The droplet was found to take a shape close to a spherical cap in the range of the drop growth rate 0.005 ml/s – 0.16 ml/s. At higher rates (0.32 ml/s and higher) liquid splashing was observed.

Crystal Growth Behavior of Methane Hydrate in the Presence of Liquid Hydrocarbon

This paper reports the visual observation of the formation and growth of methane hydrate crystals in the methane + decane + water three-phase quiescent system. This three-phase system is a simplified model of the condition within an oil-producing pipeline. A hydrate crystal nucleated at a random point on the water droplet surface and then became a hydrate film that covered the whole surface of the water droplet. The morphology of individual hydrate crystals grown at the water droplet surface were triangular or polygonal. The hydrate crystal size and the hydrate-covered water droplet shape distinctly varied depending on the system subcooling (ΔTsub). The hydrate crystal size got smaller and more slender with the increase in subcooling, and the hydrate-covered water droplet shape collapsed even more at a lower subcooling. To estimate the effect of non-hydrate-forming liquid existence, we compared the observational results obtained in the systems with and without liquid hydrocarbon. Although the liquid hydrocarbon phase offers the resistance of the mass transfer of methane, the observations indicate that the results observed in the systems with liquid hydrocarbon are similar to the results observed in the system without liquid hydrocarbon. It turns out that the controlling process for the methane hydrate crystal growth would exist within the liquid water phase. It would be possible to transfer the observational results obtained from the system without liquid hydrocarbon to the hydrate growth behavior in the system with liquid hydrocarbon, which is relevant to the condition within an oil-producing pipeline.

Icephobicity of polydimethylsiloxane-b-poly(fluorinated acrylate)

A facile process to fabricate icephobic surfaces was developed by spin-coating the polydimethylsiloxane-b-poly(fluorinated acrylate) (PDMS-b-PFA) block copolymers on the substrate. The surface microstructure and chemical composition of the block copolymer films can be adjusted by changing the PDMS content. Icephobic properties of the copolymer surface were mainly ascribed to “flexible-hard” microphase separation and the ratio of fluorine to silicon. The appropriate microphase domain size and the fluorine/silicon ratio could weaken the interaction of ice and copolymer surface and delay icing of water droplets on the copolymer surface. The copolymers containing 15wt.% PDMS showed the most outstanding icephobicity by depressing the interaction between ice and the copolymer surface.

Glycaspis brimblecombei Moore, 1964 (Hemiptera: Psyllidae) on eucalyptus: oviposition non-preference and antibiosis

Forest plantations with Eucalyptus spp. (L’ Her) in Brazil are highly yielding. However, this activity is more and more threatened due to interactions with phytophagous insects, especially by exotic species, such as the red gum lerp psyllid Glycaspis brimblecombei Moore (Hemiptera: Psyllidae). This study aimed to evaluate the resistance in eucalyptus against the psyllid in oviposition and biological development assays, attempting to identify potential genotypes resistant to the pest for forest plantations. In addition, we tested the hypothesis of that concentration of total phenolics and lignin, and amount of epicuticular wax were associated with the expression of resistance. Results showed that there was variation in the levels of resistance among the genotypes assessed. Oviposition non-preference was observed on Eucalyptus citriodora (Hook) in free-choice and no-choice tests, and Clone FP10 was least preferred in the no-choice test. The genotypes E. citriodora and Clone FP6 provided 100 % nymphal mortality, and Clones FP7 and FP9 also affected negatively the G. brimblecombei development by lengthening the duration of the nymphal stage and reducing adult emergence. Clone FP6 had higher concentration of total phenolics and larger contact angle formed between the water droplet and leaf surface, which may be associated with thicker layer of epicuticular wax on the leaves, and one of the causes of high nymphal mortality. Thus, the use of the resistant genotypes of eucalyptus screened against G. brimblecombei is a promising and viable alternative for forest plantations infested with this pest.

Spectroscopic signatures of ozone at the air-water interface and photochemistry implications.

First-principles simulations suggest that additional OH formation in the troposphere can result from ozone interactions with the surface of cloud droplets. Ozone exhibits an affinity for the air-water interface, which modifies its UV and visible light spectroscopic signatures and photolytic rate constant in the troposphere. Ozone cross sections on the red side of the Hartley band (290- to 350-nm region) and in the Chappuis band (450-700 nm) are increased due to electronic ozone-water interactions. This effect, combined with the potential contribution of the O3 + hν → O((3)P) + O2(X(3)Σg(-)) photolytic channel at the interface, leads to an enhancement of the OH radical formation rate by four orders of magnitude. This finding suggests that clouds can influence the overall oxidizing capacity of the troposphere on a global scale by stimulating the production of OH radicals through ozone photolysis by UV and visible light at the air-water interface.

Morphology study of methane–propane clathrate hydrates on the bubble surface in the presence of SDS or PVCap

The characteristics of methane–propane hydrate crystal growth on the surface of gas bubble in pure water were investigated using optical microscope and compared with those in aqueous solutions of sodium dodecyl sulfate (SDS) or poly-N-vinylcaprolactam (PVCap). Most of morphology works in literature mainly focused on the hydrate crystal growth at the gas/water interface or surface of water droplets. However, this study monitors crystal growth at the bubble surface. In the case of pure water, smooth hydrate film was formed initially and the film surface on the bubble became rough as experiment proceeded. It was also observed that the hydrate crystals developed as the dendritic shape from the surface of hydrate film. In the presence of SDS, drastic changes in morphology were observed in that smoke-like crystals appeared from the top of the bubble. Besides, the gas bubble was not fully covered by hydrate film when the SDS concentration increased. In the PVCap solution, seed-like or small spot of hydrate crystals occurred sparsely on the bubble surface and spread out the whole surface as experiment progressed. The experimental results showed that the presence of SDS or PVCap affect morphological characteristics of methane–propane hydrate crystal on the surface of gas bubble.

Visualization of Effects of Ultrasound on Liquid Droplet Solidification and Frost Formation on Cold Flat Surface

An experimental study was conducted to study the effect of ultrasonic vibrations on frost suppression on a cold flat surface in atmospheric air flow. A microscopic visualization on the liquid droplet solidification and frost formation process with and without the effect of 20-kHz ultrasound was made. The water droplets solidification and frost crystal growth on the solidified water droplet surface were comparatively observed. Meanwhile, the frost thickness variations were comparatively analyzed. It was found that almost no difference can be seen between the water droplet solidification onset time with the effect of ultrasound and that without the effect of ultrasound. However, after the water droplet solidifies, almost no growth of the frost crystal can be observed on the solidified water droplets surface with the effect of ultrasound. In addition, during the whole frost formation progress, very small growth of the frost layer can be seen on the flat surface with the effect of ultrasound. The experimental results showed that the frost growth process on the cold flat surface can be significantly restrained due to the effect of ultrasound.

Does the Homogeneous Ice Nucleation Initiate in the Bulk Volume or at the Surface of Super-Cooled Water Droplets? A Review

The formation of ice in clouds can occur through primary processes, either homogeneously or heterogeneously triggered by aerosol particles called ice nuclei, as well as through secondary processes. The homogeneous ice nucleation process involves only pure water or solution droplets. Homogeneous freezing is crucial for the microphysics in the formation of high-altitude cirrus and polar stratospheric clouds, and also in the glaciation of thunderclouds, at temperatures below about 235 K. Nucleation rates in supercooled water have been measured using different experimental techniques: expansion cloud chambers, water-in-oil emulsions, levitation methods, free falling droplets, supersonic nozzles, field measurements, and molecular dynamics simulations. An important question concerns the possibility that the nucleation process in supercooled water can occur not only in the interior volume of the droplet, but even at or close to its surface. Even if there is no conclusive evidence, the majority of experimental and theoretical results suggest that the contribution of surface nucleation increases with decreasing radius of the supercooled droplets, and the surface (or sub-surface) nucleation rate is prevalent for droplets with radius lower than about 5 μm. If homogeneous freezing initiates at the droplet surface, the freezing rate should depend on the droplet size, and even a slight contamination by molecules within the surface layer could hamper the rate of the nucleation process.