Effects Of Liquid Surface Tension Research Articles

Collapsing and Splashing Dynamics of Single Laser-Induced Cavitation Bubbles within Droplets

In the present paper, the cavitation bubble dynamics model for a single bubble oscillating within a droplet is improved based on the classical Rayleigh–Plesset bubble dynamics equation and the effects of liquid surface tension and viscosity are both considered. In the aspect of the experiment, the collapsing dynamic process of a bubble within a droplet is carried out by building a high-speed photography experimental platform. In addition, the numerical solution of the dynamic equation for the collapse time of the bubble within the droplet is also carried out. The findings are given as follows: (1) The bubble dynamic equation considering liquid surface tension and viscosity of bubble within droplet is proposed. (2) The surface of liquid droplets induced by the bubble motion could be divided into three modes: no splashing, scattered splashing, composite splash consisting of scattered and flaky splash. (3) The bubble interface during the first collapsing stage could be divided into three types: spherical, conical, and fungiform. (4) The numerical solution shows an accurate prediction of the bubble collapse time within the droplet especially under the condition of medium radius ratio.

Effects of liquid surface tension on gas capillaries and capillary forces at superamphiphobic surfaces

The formation of a bridging gas capillary between superhydrophobic surfaces in water gives rise to strongly attractive interactions ranging up to several micrometers on separation. However, most liquids used in materials research are oil-based or contain surfactants. Superamphiphobic surfaces repel both water and low-surface-tension liquids. To control the interactions between a superamphiphobic surface and a particle, it needs to be resolved whether and how gas capillaries form in non-polar and low-surface-tension liquids. Such insight will aid advanced functional materials development. Here, we combine laser scanning confocal imaging and colloidal probe atomic force microscopy to elucidate the interaction between a superamphiphobic surface and a hydrophobic microparticle in three liquids with different surface tensions: water (73 mN m−1), ethylene glycol (48 mN m−1) and hexadecane (27 mN m−1). We show that bridging gas capillaries are formed in all three liquids. Force-distance curves between the superamphiphobic surface and the particle reveal strong attractive interactions, where the range and magnitude decrease with liquid surface tension. Comparison of free energy calculations based on the capillary menisci shapes and the force measurements suggest that under our dynamic measurements the gas pressure in the capillary is slightly below ambient.

Effects of SDS surface-active agents on hydrodynamics and oxygen mass transfer in a square bubble column reactor: Experimental and CFD modeling study

This work examined experimentally and numerically the effects of sodium dodecyl sulfate (SDS) surfactant agent on mass transfer coefficients kLaL and kL in a high-aspect square bubble column reactor. To this end, SDS aqueous solutions at concentrations between 5 ppm and 30 ppm were prepared. Superficial gas velocity was varied from 0.74 cm.s−1 to 9.44 cm.s−1 covering all flow regimes to analyze the interaction between different phases and the effect of liquid surface tension on gas-liquid interfaces. Experimental data indicated that the presence of the SDS in the liquid phase augmented the overall gas holdup up to 25% at a constant gas velocity (Ug = 7.3 cm.s−1) in the transition regime, which is due to the role of SDS in bubble interactions. The impact of SDS addition on the mass transfer is twofold. Firstly, it reduced kL because the SDS molecules migrate towards the bubble-liquid interface thanks to the lower O2 diffusivity in water, thus hindering the O2 transfer from one phase to the other. Secondly, it increased aL owing to the inhibition of bubbles coalescence and, therefore, the lower mean bubble size. Among these two effects, the latter is prevailing, which led to an increase in kLaL in contaminated systems. In the second part of this work, a population balance model (PBM) was coupled with a computational fluid dynamics (CFD) model based on large-eddy simulation (LES) to analyze the effect of both tap water and SDS contaminated systems on the breakage phenomena, local flow pattern, and the resulting hydrodynamics and mass transfer features in the reactor. Ultimately, experiments and numerical simulations agreed well in terms of global gas holdup and kLaL coefficient. In particular, the transition points in the case of the SDS media (except for foam formation) provided the model with adequate PBM definitions for the dispersed phase.

Droplet impact dynamics over a range of capillary numbers and surface wettability: Assessment of moving contact line models and energy budget analysis

Bouncing and non-bouncing impact dynamics of a droplet on a solid surface are studied experimentally and numerically. High-speed visualization and an in-house dual-grid level-set method based solver are employed. Two established contact angle models, namely, Kistler and Fukai models, are implemented in the solver. While the Kistler model employs a time-varying dynamic contact angle, the Fukai model accounts for a quasi-dynamic contact angle based on contact line velocity. Better agreement between the present numerical result and present as well as published experimental results of a dynamic contact angle is found for the Kistler model, specifically for more transient contact angle variations cases that correspond to the less viscous droplets on the hydrophilic surfaces (Ca = 0.005–0.037 and θeq = 22°–90°). This is because the Kistler model can replicate more dynamic variations of the contact angles during spreading and receding as compared to the Fukai model, while both the Fukai and Kistler models numerical results are found in good agreement with the measurements for less transient contact angle variations cases that correspond to the high viscous droplets on the hydrophilic/hydrophobic surfaces (Ca = 7.596 and θeq = 86°–125°). Finally, the coupled effects of liquid surface tension, liquid viscosity, substrate wettability, and impact velocity during droplet bouncing and non-bouncing are presented through an energy budget analysis. At a given impact velocity, for less-viscous and less-surface tension liquids, the viscous dissipation is substantial irrespective of the surface wettability, whereas for less-viscous and high-surface tension liquids, the viscous dissipation is smaller on hydrophobic surfaces as compared to that on hydrophilic surfaces.

Effects of surface tension on the dynamics of a single micro bubble near a rigid wall in an ultrasonic field

Acoustic cavitation is a very important hydrodynamic phenomenon, and is often implicated in a myriad of industrial, medical, and daily living applications. In these applications, the effect mechanism of liquid surface tension on improving the efficiency of acoustic cavitation is a crucial concern for researchers. In this study, the effects of liquid surface tension on the dynamics of an ultrasonic driven bubble near a rigid wall, which could be the main mechanism of efficiency improvement in the applications of acoustic cavitation, were investigated at the microscale level. A synchronous high-speed microscopic imaging method was used to clearly record the temporary evolution of single acoustic cavitation bubble in the liquids with different surface tension. Meanwhile, the bubble dynamic characteristics, such as the position and time of bubble collapse, the size and stability of the bubbles, the speed of bubble boundaries and the micro-jets, were analyzed and compared. In the case of the single bubbles near a rigid wall, it was found that low surface tension reduces the stability of the bubbles in the liquid medium. Meanwhile, the bubbles collapse earlier and farther from the rigid wall in the liquids with lower surface tension. In addition, the surface tension has no significant influence on the speed of the first micro-jet, but it can substantially increase the speed of second and the third micro-jets after the first collapse of the bubble. These effects of liquid surface tension on the bubble dynamics can explain the mechanism of surfactants in numerous fields of acoustic cavitation for facilitating its optimization and application.

High sensitivity liquid level sensor based on a hollow core fiber structure

A high sensitivity liquid level sensor formed by using a 15-mm-long hollow core fiber sandwiched between two single mode fibers is proposed and experimentally demonstrated. The sensing principle bases on the leakage of resonant light propagating in cladding of the hollow core fiber when the sensor is partially immersed in the measured liquid in a horizontal manner. High sensitivity of 7.64 and 9.74 dB/mm are achieved for liquid level measurements of water and ethanol, respectively. The maximum measurement range is 2.2 mm for water, which is limited but much larger than diameter of the fiber due to the effect of liquid surface tension. The high sensitivity property makes the proposed sensor a potential candidate for discrete liquid level measurement, especially for some flammable and explosive liquids.

Contact angle measurement on porous substrates: Effect of liquid absorption and drop size

The contact angle Θ measured on rough, absorbing substrates is known to decrease with proceeding imbibition of the drop. We demonstrate that the impact of three absorption related parameters (absorption rate, drop size and residence time) on the measured contact angle is comprehensively captured by the relative absorbed drop volume, i.e. the percentage of the drop volume penetrated into the substrate. We analyzed a wide range of drop volumes (30 pl to 4 μl, spanning a factor 105) on substrates with very different liquid absorption rates (6–710 ml m−2s−1). Also the effect of liquid surface tension (26.8–73 mN m−1) and the effect of evaporation have been evaluated. Analyzing the development of drop volume and contact angle over time one can identify the regimes of (1) surface roughness filling and (2) bulk penetration. Independent of drop size, absorption rate and drop residence time the contact angle decreases between ~0. 5° to ~1. 2° for each percentage point of drop volume penetrated into the substrate. Thus, the relative amount of absorbed drop volume fully captures the combined effect of drop size, contact time and substrate absorption rate on the contact angle measurement, it can be used to estimate the effect of liquid penetration on the measured contact angle. The effect of evaporation was negligible for most water based liquids. In conclusion, contact angle values measured on absorbing substrates can only be compared for the same percentage of absorbed drop volume, e.g. when 30% of the drop volume has been absorbed.

Understanding the dynamic pore wetting by 1H LF NMR characterization. Part 2: Effect of liquid surface tension

The first paper (Part 1) of this study fully described the effect of the dynamic viscosity of liquids on dynamic pore wetting of porous materials. The surface tension, as an important physical properties of liquids may also play a vital role in the pore wetting process. However, the quantitative characterization of dynamic pore wetting is difficult. Thus, this paper (Part 2) investigated the effect of liquid surface tension (mixture of 1-propanol and pure water in different proportions) on dynamic wetting of pores of different sizes in hydrophilic and hydrophobic active carbon by a 1H low-field nuclear magnetic resonance (1H LF NMR), and the quantitative model between surface tension and pore wetting percentage was built. The Crispation number of liquids in the pores of different sizes was calculated. For the hydrophilic samples, the wetting processes of pores of different sizes (except for mesopores) were not changed with the surface tension. For the hydrophobic sample, the liquid with lower surface tension achieved a higher pore wetting percentage and the order of pore wetting rate was: micropores > transition pores > mesoproes. The 60-min wetting percentages in pores of different sizes showed a linear decrease relationship with the surface tension. As the Crispation number increased, the 60-min wetting percentages in different pore sizes had a first-order linear increase trend. This paper not only provides a novel method for characterizing the dynamic pore wetting of porous materials, but also have a significance for regulating pore wetting process.

Experimental analysis of the effects of liquid phase surface tension on the hydrodynamics and mass transfer in a square bubble column

The effects of liquid surface tension were investigated on gas-liquid interfaces in bubbly flows through the analysis of hydrodynamic and mass transfer features. Tap water and aqueous solutions with two types of surfactant (cationic and anionic) are used as aqueous liquid phases. In fact, these surfactants are organic collectors consisting of an amine and ester. The influences of surfactant concentration and superficial gas velocity on the volumetric mass transfer coefficient and the gas hold-up were highlighted. The experimental findings revealed that although the two surfactants tested generated a decrease in surface tension, their effects on gas hold-up and flow regimes are very different. First, it was observed that the gas hold-up in amine aqueous solutions was very close to that in tap water, but it increased once the superficial gas velocity was above 7 cm.s−1. Conversely, the presence of ester decreased the overall gas hold-up since bubble net coalescence was enhanced, and the heterogeneous flow regime prevailed above 2.9 cm.s−1. Thus, the homogeneous regime prevailed with superficial gas velocity less than 4.4 cm.s−1 for tap water and amine aqueous solution, which corresponds to the transition point. Experimental findings exhibited also that the power spectral density of pressure fluctuations is a convenient tool to identify the prevailing flow regimes even in surfactant aqueous solutions. Besides that, both organic surfactants strongly reduced the volumetric mass transfer coefficient in comparison to tap water, mainly by inducing an additional resistance to gas-liquid mass transfer through interfacial adsorption for the cationic amine, but by promoting bubble coalescence for the anionic ester aqueous solution.

Effect of liquid surface tension on the filtration performance of coalescing filters

Fibrous coalescing filters are used to collect droplets from air streams and are widely applied in the process industry but liquid surface tension affects the filter performance. In this work, the wet pressure drop, saturation, liquid distribution, and filtration efficiency of both oleophilic and oleophobic filters were investigated using four liquids with different surface tensions but similar densities and viscosities to produce aerosols. The results showed that an increase in surface tension accelerated the evolution of the wet pressure drop of filters. The jump pressure drop increased significantly while the excess channel pressure drop was constant with growing surface tension. The average saturation in the channel layers decreased as the surface tension increased and the decrease rate was much greater in oleophobic than oleophilic filters. The liquid distribution was also influenced by the surface tension. In oleophilic filters, higher surface tension led to a smaller number of channels and a larger size per channel. The channel boundaries were difficult to distinguish when the relative wettability between the liquid and filter media was very high or very low. Both oleophilic and oleophobic filters showed higher filtration efficiency at steady state in both sub-micrometer and micrometer droplet-size ranges when separating liquids with a larger surface tension. Additionally, superoleophilic and superoleophobic filters were prepared through a dip-coating method. When compared with untreated (oleophilic) and superoleophilic filters, the superoleophobic filters had the best overall performance for each liquid type due to the greatly reduced liquid hold-up.

Effect of liquid droplet surface tension on impact dynamics over hierarchical nanostructure surfaces.

Analyzing impact dynamics is important for practical applications of superhydrophobic surfaces, because these nonwetting surfaces frequently encounter impacting liquid droplets in real environments. Thus, various studies have been conducted to investigate impact dynamics by examining the correlation between the behaviors of impacting liquid droplets and several determining parameters, such as impacting velocity, surface structure and surface energy. The impacting behaviors of pure water droplets were the main focus in most previous studies; the effect of surface tension, another critical parameter, on impact dynamics has rarely been investigated. In the current work, we have newly studied the effects of liquid surface tension on impact dynamics using an ethanol-water solution as a model liquid system. We systematically varied the liquid's surface tension between 72 and 32 mN m-1 by changing the ethanol concentration from 0 to 20 wt%. This range of composition drastically changed the surface tension while it did not significantly affect other physical properties, such as density and viscosity. For an impact dynamics study, two surfaces, namely ZnO nanowires (NWs) and ZnO/Si hierarchical (HIE) structures, were prepared. As the surface tension decreased, the static water contact angle (CA) decreased on both surfaces. Under dynamic conditions, our analysis using a high-speed camera and a quartz crystal microbalance (QCM) showed that lowering the surface tension causes the transition from the anti-wetting to wetting state. The transition We numbers were obtained on both surfaces for various surface tensions of liquids. Under the same dropping conditions of liquids, the ZnO/Si HIE surface shows higher transition We numbers than the ZnO NW surface, which is due to the higher fraction of air pockets in the hierarchical structure, originating from dual dimensional structures. To understand the mechanism of dynamic transition, we developed a model for ZnO/Si HIE structures based on three determining pressures: anti-wetting, wetting, and effective water hammer pressures. The modeling results explain the experimental observations. The results of our model system are highly useful for understanding the impact dynamic behaviors of various liquids on non-wetting surfaces.

Progress of Research on the Scale Effect of Liquid Surface Tension and Tolman Length

Progress of Research on the Scale Effect of Liquid Surface Tension and Tolman Length

RELATIONSHIP BETWEEN CONTACT ANGLE HYSTERESIS AND WORK OF ADHESION OF OIL DROPLETS ON PERFLUOROMETHACRYLATESTYRENE THIN FILMS

Water and oil repellencies of flat films are crucial properties of solid materials and some biomimetric surfaces that significantly depend on surface topography and chemical compositions [1,2]. The surface wettability is expressed indirectly by the contact angle (CA) measurements of a specific liquid droplet on these surfaces [1-4]. However, in practical systems, measurement of only equilibrium CA (θe) is not enough to explain polymer surface characteristics, so advancing (θa), receding (θr) CA’s and thus the contact angle hysteresis (CAH= θa – θr) are required to accurately characterize the dewetting properties of the surfaces [1-9]. CAH of a surface is strongly affected from surface chemical heterogeneity and roughness. In addition, the relationship between the equilibrium and dynamic states (work of adhesion, Wa and CAH) is also an important parameter for the characterization of solid surfaces. Basically, the estimate of drop movement on a surface can be represented by Wa values, i.e., a higher Wad value causes a higher tendency of the droplet to stick on the tilt surface. In this study, the oil repellencies of flat perfluoroethyl alkyl methacrylate-styrene (Zonyl-TM-S) random copolymers, which were synthesized in a CO2-expanded monomer medium at 250 bar pressure and 80 oC were investigated with various perfluoroethylalkyl contents. Flat and transparent copolymer surfaces were formed by using dip-coated on glass slides from THF as solvent. The increase in the perfluoromethacrylate content of the flat copolymers resulted in a decrease of the total surface free energy of the flat copolymer surfaces from 19.0 to 14.2 mJ/m2. The oil repellencies of (Zonyl-TM-S) copolymers in the terms of contact angle hysteresis was compared with perfluoroethyl alkyl methacrylate-methyl methacrylate copolymer (Zonyl-TM-ran-MMA) by using oil drops with varying surface tensions between 20.9 mN/m and 26.9 mN/m. The effect of liquid surface tension and wt.% content of Zonyl-TM on oleophobicities of the surfaces were also examined. Increase in hydrocarbon chain lengths also caused an increase in the measured CA values due to the weaker adhesion interactions between the liquid drop and the solid surface. Increase in wt.% Zonyl-TM content of the copolymers resulted in a decrease in Wa values due to the increase of fluorine atoms in copolymer surfaces. The relationship between ( r a ) cosθ = cosθ − cosθ and Wa values, liquid surface tensions and also perfluoro alkyl wt.% content of the copolymer were also investigated. Furthermore, the CAH and oil repellency differences between the p(Zonyl-TM-ran-S) and p(Zonyl-TM-ran- MMA) thin copolymer films with similar Zonyl-TM contents were also compared within this work. An increase was found in CAH values with the increase of hydrocarbon liquid chain length and thus liquid surface tension. This is due to the increase in cohesion interactions between liquid molecules and resulted in a decrease in adhesion interactions between the solid surface and the liquid drop.

Dynamics of wet particles in rotating drums: Effect of liquid surface tension

A numerical model based on the discrete element method was developed to simulate the wet particle flow in a rotating drum. The model explicitly considered the capillary force between particles and liquid distribution within the packed bed. Physical experiments under similar conditions were carried out to validate the model, showing that the simulation and experiment results were quite comparable in terms of the flow patterns, maximum flow repose angle, and the frequency of avalanching. Flow properties in two different states were investigated with the focus on the effect of liquid surface tension. In the quasistatic state with the drum rotating at very low speeds, discrete avalanches were observed after the flow reached the maximum repose angle. However, flow properties had changed well before avalanches occurred. The microscopic analysis indicated that the strength caused by the capillary force reached a minimal when avalanches started. The maximum repose angle increased with increasing capillary force and their relationship was compared with the theoretical models based on the Mohr–Coulomb criterion and force balance. In the dynamic state, the bed showed continuous surface flow at weak surface tensions but transited into discrete avalanches characterized by the plough flow as the surface tension further increased. The flow became more dilated at high surface tensions with increased particle contacts and more uniform stress distribution. The energy and frequency of collisions between particles also decreased as the liquid surface tension increased and more collisions were observed in the region 4–5 particle diameters below the flow surface. The results would be useful to the development of a comprehensive understanding of the mechanisms of particle mixing and segregation.

A replica molding technique for producing fibrous chitosan scaffolds for cartilage engineering

Cartilage engineering benefits from the fabrication of random fibrous constructs, mimicking the structures found in the extracellular matrix of natural tissue, to support the attachment and proliferation of cells. Here, a novel approach is demonstrated for the production of fibers with controlled dimensions in the micron regime from the naturally derived biopolymer chitosan. The process involves filling an array of microchannels recessed into a mold surface with a solution bearing chitosan, inducing a pH-dependent coagulation, and releasing the structures from the mold into a medium where they assume random orientation. The dimensions and shape of these channels in the master template were defined by a standard photolithographic process followed by anisotropic reactive ion etching of the underlying silicon wafer. Replica castings of this silicon wafer surface in elastomeric polydimethylsiloxane (PDMS) served as the mold for chitosan. The resulting scaffolds were produced with fiber cross-sectional widths of 22 ± 4 µm, 13 ± 3 µm, 4.7 ± 1.6 µm, 1.7 ± 0.6 µm, and 1.1 ± 0.4 µm and were found to consist of 97.8 ± 0.5% medium when hydrated. Study of the nanoscale morphology of the fibers revealed that the effects of liquid surface tension play a significant role in the preservation of this open form and that lyophilization of the product is the preferred long term storage method.

Adhesive strength of fibre/polymer joints upon loading in liquids: effect of liquid surface tension

The effect of the surrounding liquid on the strength of the polymer/fibre interface was studied. For this purpose, the shear adhesive strength, τ, between an epoxy composition EDT-10 (based on diglycidyl ether of bisphenol A) and a steel wire of diameter 150 μm was tested by the pull-out technique at 20°C. Loading of the speciments was made in water, ethanol, and in their mixtures of different composition, i.e. in polar liquids with different surface tension γ: (23.5⩽γ⩽72) mN m−1. It was shown from loading the epoxy/steel wire joints in these liquids that their adhesive strength is lower than the adhesive strength of the specimens tested in air. The losses in adhesive strength do not depend on the surface tension of the surrounding liquids under investigation. The possible mechanisms of the strength decrease are discussed.

Effect of liquid surface tension on small hole distillation sieve tray pressure drop

AbstractExperimental work on a 229‐mm‐dia. air/liquid distillation simulator shows that the surface tension of a given liquid can affect the total tray pressure drop, which normally consists of the sum of dry tray pressure drop, clear liquid head, and residual pressure drop. Both the dry tray pressure drop and clear liquid head values establish correlations in the literature for their prediction. The residual pressure drop, however, has been regarded as a constant value. This is not the case and the residual pressure drop is a dynamic variable. Three different surface‐tension liquids (water, benzyl alcohol, and n‐Propanol) are used to isolate this effect. Results presented correlate the residual pressure drop in terms of the gas F‐factor, the clear liquid head, and the traditional residual head loss definition.

MASS TRANSFER AND PHASE HOLDUP CHARACTERISTICS IN THREE-PHASE FLUIDIZED BEDS

The effects of liquid surface tension (42.6 ∼ 72,4 mN/m) and viscosity (1 ∼214mPa • sn), liquid (0.01 ∼0.12m/s) and gas (0.01 ∼0.20m/s) velocities and particle sizes (1 — 8 mm) on phase holdup and mass transfer coefficient ( kLa) have been determined in a 0.142 m-I.D. × 2.0 m-high Plexiglas column. The gas phase holdup increases with liquid velocity, and the rate of increase in gas phase holdup sharply increases with gas velocity in the bed of surfactant solutions. In the beds of 1.0 and 1.7 mm glass beads, the bed contraction occurs whereas in the beds of 2.3 mm glass beads the bed contraction does not occur with an aqueous soltuion of ethanol (σ = 50.4 mN/m). The value of kLa increases with decreasing surface tension (σ ) but it decreases exponentially with increasing liquid viscosity in continuous bubble columns and three-phase fluidized beds. In three-phase fluidized beds with surfactant solutions, kLa increases with gas and liquid velocities and particle size. In three-phase fluidized beds of viscous or surfactant soltuions, kL,a can be estimated in terms of the energy dissipation rate based on the isotropic turbulence theory and a flow regime map is proposed based on the drift flux theory.

Axial dispersion characteristics in three-phase fluidized beds

The effects of liquid and gas velocities, liquid viscosity and surface tension, particle size and column diameter on the axial dispersion coefficients (D Z) of liquid phase in three-phase fluidized beds have been determined in two large (0.254 and 0.376 m-I.D.) columns. Tap water, carboxymethyl cellulose (CMC), Triton X-100 and ethanol aqueous solutions were used as the liquid phase; air as the gas phase and four different sizes of glass beads as the solid phase. The coefficient increases with increasing gas and liquid velocities in three phase fluidized beds. Whereas, the effects of liquid surface tension and liquid viscosity on D Z are found to be small. The axial dispersion coefficient decreases with increasing particle size and it sharply increases with increasing column size. The axial dispersion coefficients in terms of the Peclet number in the bubble coalescing and disintegrating regimes in three phase fluidized beds have been correlated based on the isotropic turbulence theory.

Modeling of surface tension effects in venturi scrubbing

A modified model of venturi scrubber performance has been developed that addresses two effects of liquid surface tension: its effect on droplet size and its effect on particle penetration into the droplet. The predictions of the model indicate that, in general, collection efficiency increases with a decrease in liquid surface tension, but the range over which this increase is significant depends on the particle size and on the scrubber operating parameters. The predictions further indicate that the increases in collection efficiency are almost totally due to the effect of liquid surface tension on the mean droplet size, and that the collection efficiency is not significantly affected by the ability of the particle to penetrate the droplet.