Surface Of Water Droplets Research Articles

In Vitro Gastric and Intestinal Digestion of a Walnut Oil Body Dispersion

An oil body dispersion (11.3% fat) was prepared by wet disintegration of walnuts and was then subjected to a two-step model of in vitro digestion. In a gastric environment, proteolysis by pepsin led to the destabilization and coalescence of the oil bodies. Aggregation of the coalesced oil bodies was apparent under a confocal microscope, with aggregates up to 275 μm in size. Pepsin-resistant peptides and proteins remained at the surface of the oil bodies, and some were further resistant to intestinal proteases. Under intestinal conditions, the hydrolysis of walnut triglycerides led to the spontaneous formation of a new type of multiple emulsions, ranging from 2 to 45 μm in size and with protein material inside the inner water droplets. Transmission electron microscopy revealed the presence of a liquid-crystalline phase of bile salts and lipolytic products at the surface of the oil droplets and some bile salt crystals at the surface of the inner water droplets.

The three-phase contact line shape and eccentricity effect of anisotropic wetting on hydrophobic surfaces

This paper experimentally evaluates the combined effects of eccentricity, relative spacing, and viewing directions on the wetting conditions and the three-phase contact line shapes of hydrophobic surfaces patterned with discrete micropillars. Different techniques to depict the tortuosity of the contact line between the water droplet and microstructured surfaces are presented. First, square micropillars with different values of normalized eccentricity, e*, and relative spacing, D*, were fabricated using a double casting replication technique. Subsequently, the contact angles were measured along different viewing angles by gradually rotating the sample from 0° to 180°. The contact angle distribution was found as a periodic function of the viewing angle whose period depends on the micropillar eccentricity. The results showed that anisotropy increases by increasing the micropillar eccentricity or decreasing the pillar relative spacing. However, the effect of changing the micropillar eccentricity was much more pronounced. Micropillars with e* = 0.75 and smaller D* showed maximum degrees of anisotropic wetting and droplet distortion corresponding to 7% and 15%, respectively. Using the measured droplet aspect ratio, corrugated shapes of the three-phase contact line of the micropillars were also reconstructed. Finally, a simple yet effective semi-analytical model, based on Fourier series curve-fitting of the experimental data, was developed to describe the equilibrium 3D shape of the droplet on anisotropic surfaces. Experimental and simulation results reveal that the degrees of anisotropic wetting and droplet distortion were directly proportional to the energy barriers of the system, resulting from the noncircular corrugated shape of the three-phase contact line. The obtained results may further shed light on the underlying mechanism influencing anisotropic wetting on micropatterned surfaces.

High speed camera investigation of the impingement of single water droplets on oxidized high temperature surfaces

This study investigates the influence of oxide layer over the hot surfaces on the behavior of single droplets impacting the high temperature surfaces using high speed camera. In the present work, an experimental apparatus was installed where direct contact between mono-dispersed water droplet and solid hot surface in the presence of different values of oxide layer (4.5, 6.7, 9.4 and 12.6 μm) over the hot surface was experimentally investigated. The droplets size and its velocity were controlled independently. The results presented the effects of surface oxide layer, droplet velocity, droplet size and surface superheating on the hot solid–liquid contact wettability time and on the maximum droplet spread diameter on the hot surface. Empirical correlations are presented describing the hydrodynamic characteristics of an individual droplet impinging on a heated surface and concealing the affecting parameters for surface oxidation phenomena in such process. Also, the comparison between the obtained results at oxidation phenomena and the results due to others at non oxidation phenomena shows the effect of surface oxidation phenomena on the behavior of single droplet impacting the high temperature surface. These experimental observations provide the validation data required for multi-phase modeling of these phenomena by computational fluid dynamics (CFD) (e.g. Volume of Fluid (VOF) modeling) methods.

Dynamic Behavior of Clathrate Hydrate Growth in Gas/Liquid/Liquid System

Variation in crystal growth behavior of clathrate hydrate depending on the temperature and pressure was visually demonstrated in the krypton-gas/liquid-cyclopentane/liquid-water system, which is expected to be a working medium of highly efficient hydrate-based heat pumps. The experiments were conducted at 28 different temperature–pressure conditions in the range from 279.0 to 299.7 K and from 0.59 to 6.44 MPa. It was found that the behavior of the hydrate crystal growth in this three-component system can be classified into three modes, which we called “cover”, “expansion”, and “line”, depending on the temperature and pressure. The descriptions of the three types are summarized as follows. Cover: the first hydrate crystals were observed at the water droplet surface and then grew to form a polycrystalline layer covering the surface. After the coverage, no more remarkable hydrate crystal growth was observed. Expansion: the first crystals were observed on the water droplet surface and grew not only along the ...

Organic molecules on the surface of water droplets – an energetic perspective

The solubility of organic molecules is a well established property, founded on decades of measurements, the results of which have been tabulated in handbooks. Under atmospheric conditions water droplets may form containing small amounts of other molecules. Such droplets typically have a very large area to volume ratio, which may shift the solvation equilibrium towards molecules residing on the droplet surface. The presence of organic molecules on droplet surfaces is extremely important for reactivity--it is well established that certain chemical reactions are more prevalent under atmospheric conditions than in bulk. Here we present a thermodynamic rationalization of the surface solvation properties of methanol, ethanol, propanoic acid, n-butylamine, diethyl ether, and neopentane based on potential of mean force (PMF) calculations--we have previously demonstrated that an energetic description is a very powerful means of disentangling the factors governing solvation (Caleman et al., Proc. Natl. Acad. Sci. U. S. A., 2011, 108, 6838-6842). All organic molecules investigated here are preferentially solvated on the surface of the droplets rather than in the inside, yet the magnitude of surface preference may differ by orders of magnitude. In order to dissect the energetic contributions that govern surface preference, we decompose the PMF into enthalpic and entropic components, and, in a second step, into contributions from water-water and solute-water interactions. The analysis demonstrates that surface preference is primarily an enthalpic effect, but the magnitude of surface preference of solutes containing large apolar groups is enhanced due to entropy. We introduce an analysis of the droplet PMFs that allows one to extrapolate the results to larger droplets. From this we can estimate the solubility of the solutes in water droplets, demonstrating that the solubility in droplets can be orders of magnitude larger than in bulk water. Our findings have implications for understanding the process of electrospray ionization, an important technique in biological mass spectrometry, since our work strongly suggests that in equilibrium biomolecules would be adsorbed on the droplet surface as well.

Crystal Growth of Clathrate Hydrate in Gas/Liquid/Liquid System: Variations in Crystal‐Growth Behavior

This paper reports the visual observations of the formation and growth of structure-II hydrate crystals on a water droplet partially immersed in liquid cyclopentane and exposed to difluoromethane gas. Each of the experiments was performed under prescribed temperature and pressure conditions in the range from 281.7 to 297.0 K and from 0.12 to 1.10 MPa in order to investigate the effect of the driving force for the hydrate crystal growth. The experiments were conducted at 25 different temperature-pressure conditions. It was found that the behavior of the hydrate crystal growth in this three-component system can be classified into three modes, which we called "cover", "expansion" and "line", depending on the temperature and pressure. The descriptions of the three types are summarized as follows. "COVER": Hydrate crystals first formed on the water-droplet surface and then grew to form a polycrystalline layer covering the surface. After complete surface coverage, no more hydrate growth and little change in the shape of the hydrate-covered water droplet were observed. "EXPANSION": Like "cover", the first crystals were observed on the water-droplet surface. They grew not only along the surface, but also toward the gas phase, and then continued to grow for more than several tens of minutes after complete coverage. "LINE": Unlike the other two modes, hydrate crystals first formed at the three-phase interfacial line and grew along this line. The shape of the hydrate crystals eventually became like a doughnut, since the center of the water droplet collapsed when they grew.

Experimental investigation of methane hydrate formation on suspended water droplets

The formation of methane hydrate films at the surface of suspended water droplets has been experimentally investigated using a novel experimental apparatus. Experiments were performed at a temperature between 273.35 and 275.15 K and a pressure between 4.01 and 6.65 MPa. The observed morphology of hydrate films showed that the growth rate of methane hydrate formed at the droplet surface is significantly increased as the supersaturation (Δ μ/ kT) is increased and the droplet size is reduced. The induction time of hydrate nucleation is influenced by the degree of supersaturation. A longer induction time was obtained at a lower supersaturation. The measured induction times were correlated to an induction time model developed based on the nucleation theory. A high value of kinetic constant and a low value of effective surface energy were obtained. The results indicated that heterogeneous nucleation of methane hydrate was occurring at the suspended water droplets. The diffusion resistance in the hydrate film was increased as the temperature was decreased and the hydrate film thickened.

Effect of Fatty Acid Composition of Monoglycerides and Shear on the Polymorph Behavior in Water‐in‐Palm Oil‐Based Blend

AbstractEffect of the fatty acid composition of monoglycerides and shear on the polymorphic behavior in a water‐in‐oil (W/O) emulsion semi‐solid fats blend was investigated. The bulk fat blend and the W/O emulsion fat blend with added either unsaturated or saturated monoglycerides were prepared using a rapid cooling heat exchanger, and the polymorphic transitions from β′ to β‐form during storage were compared by X‐ray diffraction. The peak intensity of the β‐polymorph of the samples with added saturated monoglycerides was stronger than that of unsaturated monoglycerides, and the peak intensity of the β‐polymorph of the W/O fat blend emulsions was stronger than that of the bulk fat blends. The polymorphic transition to the β‐form during storage of the W/O emulsion fat blend was promoted by the applied shear. In contrast, that of the bulk fat blend was retarded by shear. These results suggested that fatty acids, which combined to monoglycerides on the surface of water droplets, influenced the polymorph transformation of the fat crystal network in a continuous semi‐solid fat phase because of the acyl–acyl interactions between the fatty acid residues of the monoglycerides and triacylglycerols in the fat crystal network.

An overview of current issues in the uptake of atmospheric trace gases by aerosols and clouds

Abstract. A workshop was held in the framework of the ACCENT (Atmospheric Composition Change – a European Network) Joint Research Programme on "Aerosols" and the Programme on "Access to Laboratory Data". The aim of the workshop was to hold "Gordon Conference" type discussion covering accommodation and reactive uptake of water vapour and trace pollutant gases on condensed phase atmospheric materials. The scope was to review and define the current state of knowledge of accommodation coefficients for water vapour on water droplet and ice surfaces, and uptake of trace gas species on a variety of different surfaces characteristic of the atmospheric condensed phase particulate matter and cloud droplets. Twenty-six scientists participated in this meeting through presentations, discussions and the development of a consensus review. In this review we present an analysis of the state of knowledge on the thermal and mass accommodation coefficient for water vapour on aqueous droplets and ice and a survey of current state-of the-art of reactive uptake of trace gases on a range of liquid and solid atmospheric droplets and particles. The review recommends consistent definitions of the various parameters that are needed for quantitative representation of the range of gas/condensed surface kinetic processes important for the atmosphere and identifies topics that require additional research.

Metastable states during dissociation of carbon dioxide hydrates below 273 K

In this study, the dissociation of isolated carbon dioxide hydrate particles of sizes in the range 0.25–2.5 mm was investigated. It was found that below the ice melting point, the hydrates dissociated into supercooled water (metastable liquid) and gas. The formation of the liquid phase during CO 2 hydrate dissociation was visually observed, and the pressures of the hydrate dissociation into supercooled water and gas were measured in the temperature range 249–273 K. These pressures agreed well with the calculated data for the supercooled water–hydrate–gas metastable equilibrium ( Istomin et al., 2006). In the P– T area on the phase diagram bounded by the ice–hydrate–gas equilibrium curve and the supercooled water–hydrate–gas metastable equilibrium curve, hydrates could exist for a long time because the metastable phase and their stability are not connected to the self-preservation effect. The growth of the metastable CO 2 hydrate film on the surface of supercooled water droplets formed during the hydrate dissociation was observed at pressure above the three-phase supercooled water–hydrate–gas metastable equilibrium pressure but still below the three-phase ice–hydrate–gas equilibrium pressure. It was found that the growth rate of the metastable CO 2 hydrate film was higher by a factor of 25 and 50 than that for methane hydrate and propane hydrate, respectively.

A new concept for titanium oxo-alkoxo-carboxylates’ encapsulated biocompatible time temperature food indicators based on arising, not fading color

New insight into the factors determining formation and stability of oxo-alkoxide carboxylates of titanium permits to design biocompatible systems for encapsulation of binary food quality inorganic dyes, such as Preussian blue, in a temperature-sensitive shell. The shells are formed spontaneously on hydrolysis of carboxylic acid-modified titanium alkoxides on the surface of water droplets containing the dye components. The complete dye is then prepared through mixing of pre-frozen encapsulated droplets which can be activated by heating to room temperature and also influenced by the storage time. The stable shells are obtained from longer chain carboxylates providing the micellar self-assembly derived constructions with increased colloid stability. The factors influencing the formation of individual crystalline oxo-alkoxide carboxylates—a process competing with the micellar self-assembly and decreasing the stability of the oxo-alkoxide carboxylate shells are discussed with the starting point in the molecular structures of the known compounds and also the new complexes Ti6O6(OAc)6(OiPr)6 · C6H14 (1) and Ti12O12(OAc)6(OnPr)18 (2).

1D Cu(OH)2 Nanomaterial Synthesis Templated in Water Microdroplets

For many applications, micro- and nanostructured materials show a strong correlation between their geometry and their function. We report here the interfacial precipitation of a copper/alkylamine complex to form Cu(OH)(2) nanofibers in a two-phase system (H(2)O/CH(2)Cl(2)). Their aggregation results in porous microbeads. This mesoscale aggregation is due to the formation of a water-in-oil (W/O) emulsion. The fibers formed at the H(2)O/CH(2)Cl(2) interface adsorb on the water droplet surface leading to spherical networks of Cu(OH)(2) fibers. Our preparation technique is rapid (less than 1 h) and benefits from the simplicity and the tunability of emulsions.To our knowledge, this is the first demonstration of the in situ synthesis of 1D nanostructures that self-assemble at both the surface and the inside of emulsion droplets. We report the successful control over the chemical nature of the synthesized material, its size, and morphology at both the mesoscale (completely hollow versus porous) and the nanoscale (nanoribbons versus nanofibers) by the addition of a short chain alcohol. The transformation of these materials into porous CuO spheres has several potential applications, including a demonstrated sensitive response to visible light (measured photocurrent/dark current ratio of 2.22).

Role of Bitumen Components in Stabilizing Water-in-Diluted Oil Emulsions

Role of bitumen components in stabilization of water-in-diluted oil emulsions was studied using the micropipette technique. Naturally occurring components of bitumen, asphaltenes and maltenes were separated (by precipitating asphaltenes with n-pentane) to investigate their influence on the properties of water drop surfaces in Heptol (a mixture of heptane and toluene at a 4:1 volume ratio). The Heptol−water interfacial tension decreased with increasing adsorption of surface active components from both asphaltenes and maltenes. Rigidity of emulsified water droplet surfaces was observed in the presence of asphaltenes dissolved in Heptol. The observed surface crumpling is attributed to the irreversible adsorption of asphaltenes on the emulsified water droplet in Heptol. Further, the results of droplet interaction experiments indicated that the stability of the water-in-diluted oil emulsions was mainly due to the presence of asphaltenes dissolved in Heptol. However, it was observed that the presence of maltenes can also contribute to the emulsion stability even without well-defined skin formation on the emulsified water droplet surfaces.

Facile fabrication of well-defined hydrogel beads with magnetic nanocomposite shells

Well-defined magnetic nanocomposite beads with alginate gel cores and shells of iron oxide (γ-Fe 2O 3) nanoparticles were prepared by self-assembly of colloidal particles at liquid–liquid interfaces and subsequent in situ gelation. Fe 2O 3 nanoparticles could spontaneously adsorb onto the water droplet surfaces to stabilize water-in-hexane emulsions. Water droplets containing sodium alginate were in situ gelled by calcium cations, which were released from calcium-ethylenediamine tetraacetic acid (Ca-EDTA) chelate by decreasing pH value through slow hydrolysis of d-glucono-δ-lactone (GDL). The resulting hybrid beads with a core–shell structure were easily collected by removing hexane. This facile and high efficient fabrication had a 100% yield and could be carried out at room temperature. Insulin microcrystal was encapsulated into the hybrid beads by dispersing them in the aqueous solution of alginate sodium in the fabrication process. The sustained release could be obtained due to the dual barriers of the hydrogel core and the close-packed inorganic shell. The release curves were nicely fitted by the Weibull equation and the release followed Fickian diffusion. The hybrid beads may find applications as delivery vehicles for biomolecules, drugs, cosmetics, food supplements and living cells.

Revealing of water surface pollution with liquid marbles

Floating of “liquid marbles” on the surface of water contaminated with organic compounds was studied. Marbles were obtained with spreading of hydrophobic polyvinylidene fluoride particles on the surface of water droplets. Marbles floated stably on the water surface, whereas they were destroyed on the water surfaces contaminated with silicon oil and kerosene. Limiting conditions of floating were studied experimentally with the water/alcohol mixtures.

Microencapsulation of hydrophilic solid powder as a flame retardant with epoxy resin by using interfacial reaction method

AbstractMicroencapsulation of Bistetrazol · diammonium (BHT · 2NH3) as a hydrophilic powdery flame retardant was tried by the interfacial reaction method in reverse emulsion. In this microencapsulation method, water droplets containing BHT · 2NH3 and hydrazine as gelation agent for epoxy resin were dispersed in the continuous phase of corn oil. When epoxy resin was added to the continuous phase, BHT · 2NH3 as a core material was microencapsulated by the reaction of epoxy resin with hydrazine on the interface between the surface of water droplet and the continuous phase. The content of the core material from 70 to 85%, and the microencapsulation efficiency from 89 to ca 100% were able to be attained under the experimental conditions adopted here. Copyright © 2009 John Wiley & Sons, Ltd.

Liquid marble formation using hydrophobic powders

Abstract This work aims to investigate and quantitatively measure “liquid marble” phenomena using hydrophobic powders (granules). The hydrophobic powders based on a copper substrate were prepared by a silver deposition technique of particle sizes 9 μm, 20 μm and 320 μm and of contact angle with water approaching 160°. The hydrophobic powder poly-methylmethacralate (PMMA) particle size 42 μm and contact angle of 120° was also used to determine the effect of powder density on liquid marble stability. The experimental investigations indicated that for successful formation of liquid marbles a number of variables in addition to hydrophobicity need to be considered, namely: powder density; powder particle size; powder shape; liquid marble formation technique. It was found that liquid marbles were formed using all four powders to varying extents, with a low powder particle size forming more stable liquid marbles. In a series of gravimetric tests, adhered powder mass on liquid marbles was found to be directly proportional to the water droplet surface area. A more complete coverage of the water drops were found with PMMA powder than the hydrophobic granules. Moreover, a further procedure was developed to increase the mechanical strength of the liquid marble, by polymerising methylmethacrylate (MMA) on the surface of a PMMA powder – liquid marble, with the aim of maintaining water within a more robust PMMA – liquid marble shell. This technique may prove to be a novel way of encapsulating drug compounds, such as gentamicin sulphate, for PMMA bone cement.

Teflon is Hydrophilic. Comments on Definitions of Hydrophobic, Shear versus Tensile Hydrophobicity, and Wettability Characterization

Comments are made concerning the recent use of adjectives to describe solid surfaces that exhibit anomalously high water contact angle values. We suggest that the meaning of the word hydrophobic be resolved before it is modified, for example, to superhydrophobic and further modified, for example, to sticky superhydrophobic and before the definitions of these new words become issues of contention. The case is made that the first statement in the title is appropriate with experiments that demonstrate significant attractive interaction between liquid water and the surface of solid Teflon. Four types of experiments are described: the interaction of a silicon-supported covalently attached perfluoroalkyl monolayer (a model Teflon surface) with a sessile water drop (1) and with a thin film of water on a clean silicon wafer surface (2), the interaction of 1 and 12 microm diameter solid Teflon particles with a water droplet surface (3), and the interaction of a thin (<5 microm) Teflon film with a water droplet (4). The concepts of shear and tensile hydrophobicity are introduced, and the recommendation that two numbers, advancing and receding contact angle values, should be considered necessary data to characterize the wettability of a surface. That the words hydrophobic, hydrophilic, and their derivatives can and should only be considered qualitative or relative terms is emphasized.

Influences of water droplet size and pollution layer permittivity on the electric field and potential distribution on a polluted insulator surface

Abstract:Presence of water droplets on a polluted outdoor high voltage insulator surface modifiesthe electric field flux and the equipotential distribution along the insulator surface. Thewater droplet may appear in different forms and sizes. The form is defined, here, by theangle shape between the water droplet surface and that of the insulator, which is keptconstant at 90 degrees. The droplet size is specified by the diameter. The water dropletmay measure from less than 90 degrees (hydrophilic) up to greater than 90 degrees(hydrophobic), depending on the properties of insulator surface.The present work describes a detailed numerical computation of the electric field andthe potential distribution in the surroundings of water droplet on a polluted insulatorsurface. The computations are carried out using the Femlab package 3.1, which is basedon the finite element method.The parameters used in the numerical analysis are the size of the water droplet and thepollution layer permittivity which describes the possible wetting conditions of the layer(i.e. clean, semi-wetted, and fully-wetted polymer surface). Detailed plots of thepotential and field distribution in the inter electrode space, with and without thepresence of a water droplet, were generated. The results showed that the electric fieldclose to the water droplet tends to be higher as the diameter of the droplet increases, andlower as the relative permittivity of the pollution layer increases.

Wetting transition of water droplets on superhydrophobic patterned surfaces

The relationship between water droplet size and surface geometric parameters governs the transition from composite solid–air–liquid interface to homogeneous solid–liquid interface on superhydrophobic surfaces. This study presents the effect of varying droplet size on the wetting properties of patterned Si surfaces. We propose a criterion that the transition from the Cassie–Baxter regime to the Wenzel regime occurs when the droplet droop is greater than the depth of the cavity. The trends are explained based on experimental data and in terms of the proposed transition criterion.