Changes In Surface Tension Research Articles

Rheology and air entrainment of fresh Portland cement mortars in simulated low air pressure environments

Air entrainment in cement-based materials is believed to be affected by low air pressure (AP) which is the atmospheric characteristic in high plateaus, and thus the rheology may be affected. This paper attempts to study rheology and air entrainment of fresh Portland cement mortar in simulated low APs. The results indicate that the rheological responses with the varying AP gradients are relevant to the air entrainments in fresh mortar mixtures. The volume changes of air voids in fresh mortars are linearly related to the varying APs, which is owing to not only the AP difference between the inside and outside air voids but also the additional pressure on the liquid films of air voids stemming from the surface tension changes. Moreover, the Bingham capillary number is calculated to account for the air void deformability. Then rheological parameters are correlated to the content and deformability of air voids in fresh mortars.

Study on the compounding of sodium N-lauroyl glutamate and cationic cellulose

Abstract In this work, sodium N-lauroyl glutamate (SLG) was mixed with cationic cellulose JR30 M. The rapidly occurring change in surface tension and the mass action law of the mixed (compound) system were investigated using dynamic and equilibrium surface tension methods. The behaviour of the system during phase separation was investigated by turbidimetry. The results showed that in the presence of JR30 M, the surface tension of SLG was reduced to a lower level in the given time interval due to the strong interaction compared to that of a solution with the same concentration of SLG but without JR30 M. The largest decrease was obtained with a JR30 M concentration of 0.2 g L−1, which reduced the equilibrium surface tension of SLG from 38.4 mN m−1 to 31.7 mN m−1. The rate of decrease in surface tension increased from 37.61 mN m−1 s−1 to 74.7 mN m−1 s−1. An association complex formed between SLG and JR30 M, and the equilibrium surface tension curve showed a double platform. As the concentration of JR30 M increased, the first platform broadened and the CMC value increased. The phase separation behaviour of the compound system disappeared with the increase of SLG concentration, and the area became narrower with the decrease of JR30 M concentration.

Deformation and necking of liquid droplets in a magnetic field

Pendant droplets of water and paramagnetic solutions are studied in the presence of uniform and nonuniform magnetic fields produced by small permanent magnet arrays, both in static conditions and during dynamic pinch-off. Static measurements of the droplet shape are analyzed in terms of an apparent surface tension γapp or an effective density ρeff. The change of surface tension of deionized water in a uniform field of 450 mT is insignificant, 0.19 ± 0.21 mNm−1. Measurements on droplets of compensated zero-susceptibility solutions of Cu2+, Mn2+, and Dy3+, where the shape is unaffected by any magnetic body force, show changes of surface tension of about −1% in 500 mT. Magnetic field gradients of up to 100 T2 m−1 deform the droplets and lead to changes of ρeff that are negative for diamagnetic solutions (buoyancy effect) and positive for paramagnetic solutions. The droplet profile of strongly paramagnetic 0.1 molar DyCl3 solution is analyzed, treating the nonuniform vertical field gradient as a spatial variation of gravity. The influence of Maxwell stress on the droplet shape is discussed. In dynamic measurements, the droplet shape at pinch-off is recorded by high-speed photography and analyzed in terms of a relative change of dynamic surface tension in the presence of a magnetic field. The surface-tension-dependent prefactor of the scaling law that governs the pinch-off dynamics shows no difference for pure water or 0.11 M DyCl3 solutions in the field. The nonuniform field has no influence in the pinch-off region because the filament diameter is much less than the capillary length.

Numerical Assessment of Gravity for Sloshing in Tank Using OpenFOAM

We numerically study gravity’s effect on sloshing in a two-dimensional tank which is highly filled by water (95% water and 5% air). Both fluids are considered to be incompressible and inviscid. The surface tension and phase change are neglected. OpenFOAM software is used for the simulation. A standing wave of water impacting the lid of the tank at its center and a symmetric wetted region starts to advance along the lid. The simulation carried out (only on the right-half side of the tank due to symmetric geometry of the impact) with and without gravity to investigate the influence of gravity on this impact. The numerical results are validated by comparing to published data. The effect of gravity on the size of the wetted region, free-surface elevation and on the pressure distribution has been analyzed. It is shown that gravity is affecting the free-surface elevation and consequently the size of the wetted region. These effects growth as time goes. Pressure distribution along the wetted region of the lid is also influenced by gravity.

Ionic liquid-modulated synthesis of MnO2 nanowires for promoting propane combustion: Microstructure engineering and regulation mechanism

Manganese oxides for catalytic combustion of VOCs are high profile owing to their excellent redox properties and oxygen storage capacities, while the precise regulation of microstructure to improve the activity remains challenging. Herein, imidazolium-based ionic liquids are employed as the template agents to synthesize a range of MnO2 for different structures and morphologies. The hydrogen bonding network of the ionic liquid and the π-π stacking interactions between the imidazole rings promoted the self-organization of [MnO6] into a specific structure. In this process, alteration of alkyl chain length of ionic liquids caused changes in surface tension and steric hindrance, affecting the growth of MnO2. A series of characterization results showed that MnO2 transformed from nanofibers to nanorods when the alkyl chain elongated from ethyl to octyl, accompanied by an increase in crystal size. This transformation decreased the specific surface area and surface-active oxygen of the catalyst, diminishing active sites available for the catalytic reaction. Therefore, the optimal catalytic performance of the prepared catalyst was achieved when the ionic liquid was selected as 1-ethyl-3-methylimidazolium tetrafluoroborate, with a propane conversion of 90% at 289 ºC. This work provided a feasible path to realize the microstructure engineering of non-noble metal catalysts.

In situ investigation of the oxidation of a phospholipid monolayer by reactive oxygen species

The oxidation of membrane lipids has been widely studied for several decades owing to its significance in biological systems. However, despite its damaging physiological impact and its known role in many diseases, relatively little is understood about the specific structural consequences of oxidative action, particularly in vivo. In this work, a combination of sum-frequency generation spectroscopy, surface tensiometry, and surface-selective infrared spectroscopies are used to gain deeper insight into the oxidation of phospholipids by reactive oxygen species generated in situ. Oxidation is achieved by employing the Fenton reaction to convert physiological levels of H2O2 into OH and HO2 radicals in proximity to the headgroups of lipid monolayers at the air-water interface. By temporally monitoring the surface tension and spectroscopic changes at the interface as the oxidation proceeds, the impact of oxidation on the structure, conformation, and intermolecular interactions within the membrane has been revealed.

Changes in CSF Surface Tension in Relation to Surfactant Proteins in Children with Intraventricular Hemorrhage.

The regulation of surface tension (ST) by surfactants plays an important role in the human respiratory system but is largely unexplored in brain homeostasis. The aim of this study was to evaluate changes in ST in relation to surfactant proteins (SPs) in children with intraventricular hemorrhage (IVH). CSF samples from 93 patients were analyzed for ST with a force tensiometer and SP-A-D and -G with ELISA assays. Patients belonged to six groups: (i) IVH before primary intervention (PI), (ii) IVH 4-28 days after PI, (iii) IVH 44-357 days after PI, (iv) hydrocephalus, (v) sepsis and (vi) controls. We found indirect correlations and significant differences in ST and SPs (all p < 0.001; except for SP-C, p = 0.007). Post hoc analyses showed significantly decreased ST in IVH patients before PI compared with patients with hydrocephalus, sepsis or controls (p < 0.001), but it increased in IVH patients over time. All SPs were significantly elevated when comparing IVH patients before PI with controls (all p < 0.001; except for SP-C, p = 0.003). Children suffering from IVH displayed an increase in SPs and a decrease in ST as coping mechanisms to preserve CSF flow. The increase in ST over time could serve as prognostic marker for the healing process.

Microtensiometer for Confocal Microscopy Visualization of Dynamic Interfaces.

Adsorption of surface-active molecules to fluid-fluid interfaces is ubiquitous in nature. Characterizing these interfaces requires measuring surfactant adsorption rates, evaluating equilibrium surface tensions as a function of bulk surfactant concentration, and relating how surface tension changes with changes in the interfacial area following equilibration. Simultaneous visualization of the interface using fluorescence imaging with a high-speed confocal microscope allows the direct evaluation of structure-function relationships. In the capillary pressure microtensiometer (CPM), a hemispherical air bubble is pinned at the end of the capillary in a 1 mL volume liquid reservoir. The capillary pressure across the bubble interface is controlled via a commercial microfluidic flow controller that allows for model-based pressure, bubble curvature, or bubble area control based on the Laplace equation. Compared to previous techniques such as the Langmuir trough and pendant drop, the measurement and control precision and response time are greatly enhanced; capillary pressure variations can be applied and controlled in milliseconds. The dynamic response of the bubble interface is visualized via a second optical lens as the bubble expands and contracts. The bubble contour is fit to a circular profile to determine the bubble curvature radius, R, as well as any deviations from circularity that would invalidate the results. The Laplace equation is used to determine the dynamic surface tension of the interface. Following equilibration, small pressure oscillations can be imposed by the computer-controlled microfluidic pump to oscillate the bubble radius (frequencies of 0.001-100 cycles/min) to determine the dilatational modulus The overall dimensions of the system are sufficiently small that the microtensiometer fits under the lens of a high-speed confocal microscope allowing fluorescently tagged chemical species to be quantitatively tracked with submicron lateral resolution.

Platform for Exposing Aerosolized Substances to Lung Surfactant and Alveolar Cells at the Air-Liquid Interface

Lung surfactant lowers surface tension in the alveoli, playing a critical role in lung function and immune defense. Inhaled aerosol particles may induce adverse health effects via the interruption of lung surfactant surface tension. Previous generations of surfactometers have been developed and used to characterize surfactants and their response to various exposures. However, these devices do not allow for simultaneous exposure with multiple aerosols, the incorporation of multiple aerosolization methods, or the co-exposure scenario involving both lung surfactant fluid and pulmonary cells/tissues. Herein, we introduce a new configuration, termed the aerosol exposure surfactometer (AESM), that addresses all of these limitations. The results indicate correlation of surface tension changes in concordance with aerosol properties while preventing unwanted cell death. Further investigation using this method may elucidate mechanisms of pathogenesis related to surfactant dysfunction and provide the foundation for predictive models.

Influence of tetraalkylammonium salts on the adsorption kinetics of bovine serum albumin in aqueous solutions at the air-liquid interface

Bovine serum albumin adsorption dynamics in water and in aqueous solutions of tetramethylammonium bromide, hexyltrimethylammonium bromide octyltrimethylammonium bromide, decyltrimethylammonium bromide, and dodecyltrimethylammonium bromide at the air-liquid interface was studied at a temperature of 298.15 K.The kinetics of the adsorption process of the biomolecule in water and in the aqueous alkylammonium solutions was investigated following the changes in surface tension with time. The measurements were performed on a high-precision drop volume tensiometer.The surface pressure data were adjusted with two of the most used semi-empirical kinetic models that describe the process of adsorption and allow the determination of the equilibrium adsorption parameters.The results in water and in the aqueous solutions containing tetraalkylammonium salts show that the adsorption kinetics is well described by a model consisting of three steps in which the transport of the protein in the initial stage is diffusion controlled. After some time, the rate is determined by the adsorption and the penetration of the protein at the air-liquid interface and the rearrangement of the protein at the interface; the evolution of both processes is described by steps that follow first-order rate equations.The results indicate that the overall adsorption process of bovine serum albumin BSA in water and the aqueous alkylammonium salts solutions is controlled by the second step which is the slowest of the three steps; it corresponds to the adsorption and penetration of the biomolecule at the air-liquid interface.

Effect of nanoparticles saturation on the surface tension of nanofluids

The present work focuses on the surface tension of nanofluids. An empirical model of the surface tension of nanofluids and a mechanism for the influence of nanoparticles on the value of this property are proposed. The paper explains the processes causing an increase as well as a decrease in the surface tension of nanofluids and why the value of the surface tension changes with increasing nanoparticle concentration only within a certain range. A mathematical function is presented to model this behaviour and predict both the maximum value of the surface tension and the nanoparticle concentration at which this value is reached. For the verification of the model, experimental studies of the surface tension of four types of ethylene glycol - based nanofluids indium oxide (In2O3), titanium oxide (TiO2), zinc oxide (ZnO) and multiwalled carbon nanotubes (MWCNT) at a temperature of 298.15 K were carried out. The proposed model agrees well with the obtained surface tension values of the investigated nanofluids.

Influence of various factors on surface properties of elastomeric materials based on nitrile butadiene rubbers

Objectives. The influence of the technological additive content and accelerated aging conditions on the surface energy and elastic-strength properties of nitrile butadiene rubbers with an average acrylic acid nitrile content and rubbers based on them were studied in the paper.Methods. The free surface energy of the samples was determined under the standard conditions and in the accelerated aging conditions with the use of the Owens, Wendt, Rabel, and Kaelble method.Results. It was shown that the elastomeric materials surface energy is influenced by surfactants such as rosin and stearic acid, which are typical ingredients of rubber compounds. It was also found that the thermal aging effect on the physical and mechanical properties of rubbers based on nitrile butadiene rubbers depends on the method of rubber isolation from latex and on the nature of the surfactant components in the samples.Conclusions. The analysis of the results obtained shows that the change in the vulcanizates physical and mechanical properties, depending on the technological additive content and the temperature effect, occurs along with a change in the critical surface tension.

Axisymmetric free-surface flow simulation using the moving surface mesh particle method and application to drop formation

It is difficult to accurately simulate axisymmetric free-surface flows with surface tension and topological changes, such as drop formation through a nozzle. A promising numerical method that can achieve this goal is the moving surface mesh particle method. It incorporates a moving surface mesh to explicitly represent a free-surface boundary, which enables accurate free-surface tracking and surface tension calculation. In the present study, this method is extended to an axisymmetric coordinate system. In the axisymmetric simulation, particles moving in a Lagrangian fashion result in significantly non-uniform particle distributions, leading to numerical instabilities. To circumvent this issue, a new algorithm is developed for determining the particle movement in an ALE fashion by considering a two-dimensional continuity equation. Moreover, in order to deal with the topological change arising from breakup of liquid domain, a simple algorithm employing surface mesh splitting is developed. The proposed method is verified using fundamental test cases such as axisymmetric cavity flow, axisymmetric patch test, spherical droplet oscillation, and hanging droplet. Therein, precise agreements to reference solutions are confirmed. Furthermore, the proposed method is applied to the numerical simulation of dripping faucet. As a result, complex drop formation phenomena are successfully simulated with reasonable computational cost. The numerical results are also shown to agree well with the experimental measurement in the literature, from which the validity of the proposed method is demonstrated.

Bioinspired Photo-Responsive Liquid Gating Membrane.

Stomata in the plant leaves are channels for gas exchange between the plants and the atmosphere. The gas exchange rate can be regulated by adjusting the opening and closing of stoma under the external stimuli, which plays a vital role in plant survival. Under visible light irradiation, the stomata open for gas exchange with the surroundings, while under intense UV light irradiation, the stomata close to prevent the moisture loss of plants from excessive transpiration. Inspired by this stomatal self-protection behavior, we have constructed a bioinspired photo-responsive liquid gating membrane (BPRLGM) through infusing the photo-responsive gating liquid obtained by dissolving the azobenzene-based photo-responsive surfactant molecules (AzoC8F15) in N,N-Dimethylacetamide (DMAC) into nylon porous substrate, which can reversibly switch the open/closed states under different photo-stimuli. Theoretical analysis and experimental data have demonstrated that the reversible photoisomerization of azobenzene-based surfactant molecules induces a change in surface tension of the photo-responsive gating liquid, which eventually results in the reversible variation of substantial critical pressure for gas through BPRLGM under alternating UV (PCritical (off)) and visible (PCritical (on)) light irradiations. Therefore, driven by a pressure difference ΔP between PCritical (on) and PCritical (off), the reversible switches on the open/closed states of this photo-responsive liquid gating membrane can be realized under photo-stimuli. This bioinspired membrane with switchable open/closed liquid gating performance under photo-stimuli has the opportunity to be used in the precise and contactless control of microfluidics.

Long-wave instabilities of evaporating/condensing viscous film flowing down a wavy inclined wall: Interfacial phase change effect of uniform layers

The interfacial phase change effect on a thin film flowing down an undulated wall has been investigated in the present study. The study is performed for a general periodic undulated bottom of moderate steepness that is long compared to the film thickness, followed by a case study over the sinusoidal bottom. The long-wave instabilities of the ununiform film are used by deriving a nonlinear evolution equation in the classical long-wave expansion method framework. The one-equation model can track the free surface evolution and involve the bottom undulation, viscosity, gravity, surface tension, and phase change (evaporation/condensation) effects. Linear stability analysis shows that the bottom steepness ζ has a dual role. In the downhill region, increasing ζ destabilizes, whereas increasing ζ stabilizes in the uphill region. Weakly nonlinear waves are studied using the method of multiple scales to obtain the complex Ginzburg–Landau equation. The results show that both supercritical and subcritical solutions are possible for evaporating and condensate film. Interestingly, while one subcritical region is visible for an evaporating film, two subcritical unstable regions are found for condensate film. The numerical solution of the free-surface equation demonstrates the finite-amplitude behavior that tends to dry out for an evaporating film. For condensate film, the thickness increases rapidly. The rupture dynamics highly depend on the initial perturbation, and the bottom steepness has a negligible effect on it. Kutateladze number has a significant impact on the stability characteristic of the film flow as it represents a sort of efficiency of phase change that occurs at the interface.

The Study of Novel Self-Rewetting Fluid Application to Loop Heat Pipe

The purpose of this paper is to develop SRF formulations for LHP performance enhancement. In this paper, the solute of SRF is prepared, and butanol and its isomer, 2-butanol, are selected. In this paper, concentrations of the 2-butanol aqueous solution (10%, 15%, and 20%) plus the butanol 6% aqueous solution were used to measure the surface tension of four different formulations of SRF and water. It was found that the higher the solute concentration became, the stronger the Marangoni effect was, and the more obvious the surface tension change of the 2-butanol 20% aqueous solution was. Water, the butanol 6% aqueous solution and the 2-butanol 20% aqueous solution were filled into LHP respectively, and the heat transfer performance was measured. The 2-Butanol 20% aqueous solution improved LHP performance by about three times compared with water, and the lowest total thermal resistance was only 1/4 that of water. Therefore, the 2-butanol 20% SRF aqueous solution is an ideal formula for improving the LHP heat transfer performance.

Surface tension of Fe-based Cr–Ni–Ce–O–N heat-resistant alloy

ABSTRACT The surface tension evaluation model of the Fe-based Cr–Ni–Ce–O–N heat-resistant alloy system was built, and the model shows good reproducibility. Calculations showed that nitrogen and oxygen are surface-active elements. Cerium also can work as a surface-active element with a low content of nitrogen and oxygen. The contents of O, Ce and N on the surface were higher than those in the bulk. The surface tension of heat-resistant steel in the refining process decreases due to blowing nitrogen. The effect of oxygen to reduce the surface tension is more significant. The decrease of the surface tension and periodical change of the interfacial properties caused by the ‘stirring’ effect of oxygen were helpful to promote the decarburisation process. The surface tension of the molten heat-resistant steel can stay constant with feeding Ce-wire in the Ladle Furnace (LF) refining process, which is helpful to form a stable reaction interface between the refining slag and the melt surface.

Synthesis and Physicochemical Properties of CO2-switchable Gemini Surfactants

Conventional surfactants have excellent performance but not easily recycled and sustainable. The CO2/N2 switchable Gemini surfactants can be reused while maintaining performance and can also effectively utilize greenhouse gas CO2, thereby reducing carbon emissions. In our work, three tertiary amines N, N'-dimethyl N, N'-dialkyl ethylenediamine with different hydrophobic chain lengths (CnDEs, n = 12, 14, and 16) were fabricated by a two-step process using alkyl bromide, ethylenediamine, formic acid, and formaldehyde as raw materials. Structures of intermediates and end products were characterized by FTIR and 1H NMR. The Gemini surfactants such as N,N′-dimethyl N,N′-bis (dodecane, tetradecane, and hexadecane) alkylethylenediamine bicarbonates (CnDBs, n = 12, 14, and 16) were generated by the synthetic corresponding tertiary amines after bubbling CO2. After bubbling N2, the bicarbonate surfactants were converted into tertiary amine non-surfactants again. The reversibility of the switching of three surfactants was verified by measuring the changes in surface tension, zeta potential, particle size distribution, and foaming volume before and after CO2/N2 bubbled into the tertiary amine solutions. The physicochemical properties of CnDBs were studied by thermogravimetric analysis, surface tension measurement, cation content measurement, and dissipative particle dynamics (DPD). The results demonstrated that the synthesized CO2/N2 switchable Gemini surfactants had excellent reversibility and reproducibility. The application properties indicated that the Gemini surfactants could reduce interfacial tension of oil/water to ultra-low value; possessed good cation conversion rate and decent foaming properties. Furthermore, the surfactant performances were verified through DPD simulation experiments. With the industrialization of synthetic technology, the costs of CO2/N2 switchable Gemini surfactants will effectively decrease. Storage and utilization of considerable quantities carbon dioxide promote our green low-carbon life, which are conducive to the achievement of the national strategic goal of China's carbon peak in 2035 and carbon neutralization in 2050.

Marangoni convection driven by temperature gradient near an isotropic-nematic phase transition point.

Marangoni flow driven by a temperature gradient was observed near the isotropic-nematic phase transition point. By applying the gradient to a liquid crystalline material in sandwich cells, it was possible to measure the flow field near the air interface using the photobleaching method. In the isotropic phase, the direction of the observed flow was opposite to that in the nematic phase. Moreover, when the measurement was performed in the coexistence state of these phases, the flow direction depended on the coating materials of the cell substrates. These singular flow properties are explained well by the singular changes in surface tension and the shape of the air interface near the transition point.

Changes to lung surfactant monolayers upon exposure to gas phase ozone observed using X-ray and neutron reflectivity.

Exposure to the secondary pollutant ozone in ambient air is associated with adverse health effects when inhaled. In this work we use surface pressure measurements, combined with X-ray and neutron reflection, to observe changes in a layer of lung surfactant at the air water interface when exposed to gas phase ozone. The results demonstrate that the layer reacts with ozone changing its physical characteristics. A slight loss of material, a significant thinning of the layer and increased hydration of the surfactant material is observed. The results support the hypothesis that unsaturated lipids present in lung surfactant are still susceptible to rapid reaction with ozone and the reaction changes the properties of the interfacial layer.