Terms Of Surface Tension Research Articles

Experimental Study on the Surface Tension, Density, and Viscosity of Aqueous Poly(vinylpyrrolidone) Solutions

Aqueous solutions of the polymer poly(vinylpyrrolidone) (PVP) were analyzed in terms of surface tension (Wilhelmy-Plate), density (vibrating tube density meter), and dynamic viscosity (falling ball viscometer) for different molar masses, concentrations, and temperatures. Surface tensions were determined for PVP 10, K25, and K90 at 298.15 K. Densities and viscosities were studied with PVP K25 and K90 in a temperature region from (293.15 to 310.15) K. The dynamic viscosity isotherms were fitted successfully to a basic polynomial function. The experimental data are discussed and compared to literature data.

Theory of heat transfer during condensation in microchannels

A theoretical model for condensation in microchannels takes account of the effects of gravity and streamwise shear stress on the condensate surface as well as the transverse pressure gradient due to surface tension in the presence of change in condensate surface curvature. Numerical solutions of the relevant conservation equations have been obtained for various channel shapes, dimensions, vapor-to-surface temperature differences and vapor mass fluxes. The theory is reviewed and updated. The effect of channel inclination is included and new results are presented. When using boundary conditions of uniform vapor and surface temperature it is found that, over a certain length of channel, the local mean (around the channel perimeter) heat-transfer coefficient is essentially independent of gravity and vapor shear stress. For the surface tension dominated regime, an equation for the Nusselt number as a function of a single dimensionless group, analogous to that occurring in the simple Nusselt theory except that the gravity term is replaced by a surface tension term, has been derived both on the basis of dimensional analysis and by approximate theory. The equation represents all of the data satisfactorily. This is a step towards the goal of representing the solutions, including those conditions where shear stress and gravity play important roles, by relatively simple dimensionless algebraic equations, valid for any fluid and channel geometry, for convenient use in design and optimization.

Metal-ligand coordinated Ca(DS)2/C14DMAO/H2O system: Phase behavior and rheological property

A metal-ligand coordinated surfactant system formed by calcium dodecylsulfate (Ca(DS)2)/tetradecyldimethylamine oxide (C14DMAO)/H2O was studied in terms of surface tension, conductivity, negative-staining TEM, phase behavior and rheological operation. In C14DMAO solution, when Ca(DS)2 is added, metal-ligand complexes form between the Ca2+ and N→O group of C14DMAO. Under this metal-ligand driving force, different phases can be obtained at different concentrations and different ratios of Ca(DS)2 and C14DMAO. At the fixed C14DMAO concentration, L1-phase consisting of spherical micelles forms at first. With the addition of Ca(DS)2, the spherical micelles elongate to be wormlike micelles and then after an L1/Lα-two phase region, the birefringent vesicle-phase (Lαv-phase) region is observed. When Ca(DS)2 concentration continues to increase, a gel-phase region is found after the Lαv-phase region and then precipitates of undissolved Ca(DS)2 appear. The transition between different phases is affected by temperature remarkably. The wormlike micellar solutions and vesicle solutions were checked by rheological measurements and showed apparent viscoelasticity at high surfactant concentrations.

Fluorocarbon-Hybrid Pulmonary Surfactants for Replacement Therapy - A Langmuir Monolayer Study

Effective additives to pulmonary surfactant (PS) preparations for therapy of respiratory distress syndrome (RDS) are being intensively sought. We report here the investigation of the effects of partially fluorinated amphiphiles (PFA) on the surface behavior of a model PS formulation. When small amounts of a partially fluorinated alcohol C(8)F(17)C(m)H(2m)OH (F8HmOH, m = 5 and 11) are added to the PS model preparation (a dipalmitoylphosphatidylcholine (DPPC)/Hel 13-5 peptide mixture) considered here, the effectiveness of the latter in in vitro pulmonary functions is enhanced. The mechanism for the improved efficacy depends on the hydrophobic chain length of the added PFA molecules. The shorter PFA, F8H5OH, when incorporated in the monolayer of the PS model preparation, promotes a disordered liquid-expanded (LE) phase upon lateral compression (fluidization). In contrast, the addition of the longer PFA, F8H11OH, reduces the disordered LE/ordered liquid-condensed (LC) phase transition pressure and promotes the growth of ordered domains (solidification). Furthermore, compression-expansion cycles suggest that F8H5OH, when incorporated in the PS model preparation, undergoes an irreversible elimination into the subphase, whereas F8H11OH enhances the squeeze-out phenomenon of the SP-B mimicking peptide, which is important in pulmonary functions and is related to the formation of a solid-like monolayer at the surface and of a surface reservoir just below the surface. F8H11OH particularly reinforces the effectiveness of DPPC in terms of minimum reachable surface tension, and of preservation of the integrated hysteresis area between compression and expansion isotherms, the two latter parameters being generally accepted indices for assessing PS efficacy. We suggest that PFA amphiphiles may be useful potential additives for synthetic PS preparations destined for treatment of RDS in premature infants and in adults.

On relation between the quark–gluon bag surface tension and the colour tube string tension

We revisit the bag phenomenology of deconfining phase transition aiming to replenish it by introducing systematically the bag surface tension. Comparing the free energies of such bags and the strings confining the static quark–antiquark pair, we express the string tension in terms of the bag surface tension and the bulk pressure in order to estimate the bag characteristics using the lattice QCD (LQCD) data. Our analysis of the bag entropy density demonstrates that the surface tension coefficient is amazingly negative at the cross-over (continuous transition). The approach developed allows us to naturally account for an origin of a pronounced maximum (observed in the LQCD studies) in the behaviour of heavy quark–antiquark pair entropy. The vicinity of the (tri-)critical endpoint is also analyzed to clarify the meaning of vanishing surface tension coefficient.

Effect of meconium on surface properties of surfactant monolayers and liposomes

The pathophysiology of meconium aspiration syndrome (MAS) is attributed in part to the development of lung surfactant dysfunction in vivo. Meconium (the first excrement of the newborn) and its components are responsible for development of lung surfactant dysfunction. In this study, the effect of meconium and its components on the surface activity of spread surfactant monolayers was evaluated using Wilhelmy balance at physiological temperature and pH. The effect of meconium on adsorption, airway patency and ultrastructure of liposomes made of various surfactant lipids was also evaluated. Significant inhibition of DPPC monolayer surface activity was observed on addition of meconium, its organic and aqueous phase extracts. All the surfactant lipid mixtures including DPPC attained significantly higher minimum surface tensions (between 12 and 20 mN/m) and lowered monolayer compressibility modulus in presence of meconium suggestive of surfactant monolayer fluidization. Meconium reduced the airway patency and affected the adsorption of DPPC liposomes and was associated with altered ultrastructure of DPPC liposomes. Meconium caused the maximum inhibitory effect on DPPC:PE and DPPC:PG and the least inhibitory effects on DPPC:POPC and DPPC:CHOL in terms of minimum surface tensions. All the surfactants were equally inhibited in terms of airway patency. These findings have implications for the differential inhibition of different surfactants in MAS and for the designing of surfactants that are resistant to meconium inhibition.

Characterization of the Liquid-Gas Interface of Aqueous Systems Containing a Derivative from Castor Oil

An anionic surfactant, synthesized with ricinoleic acid from castor oil, was obtained and its behavior in terms of microemulsion formation (via pseudo-ternary diagram analysis) and liquid-gas surface tension (both for microemulsions and pure surfactant-water systems) was determined as a function of temperature and NaCl concentration in the aqueous phase. Microemulsions were formed by using butanol as co-surfactant and kerosene as the oil phase. Concerning the pseudoternary diagrams, the increase in NaCl concentration resulted in a decrease in the Winsor IV region, which was correlated to a possible occurrence of nonmicellar aggregates, induced by the high concentration of NaCl in the aqueous phase. Surface tension measurements also indicated that at the very high NaCl concentrations used there could be the formation of surfactant aggregates. The oil phase in microemulsionated systems decreased surface tension (but increased CMC): Possible interactions between isolated surfactant molecules and molecules from the oil phase were used to explain these results.

Cauchy problem for viscous shallow water equations with surface tension

We are concerned with the Cauchy problem for a viscous shallow water system with a third-order surface-tension term. The global existence and uniqueness of the solution in the space of Besov type is shown for the initial data close to a constant equilibrium state away from the vacuum by using the Friedrich's regularization and compactness arguments.

INFLUENCE OF SURFACE TENSION AND BOTTOM TOPOGRAPHY ON INTERNAL WAVES

Following the global strategy introduced recently by Bona, Lannes and Saut in Ref. 7, we derive here in a systematic way, and for a large class of scaling regimes, asymptotic models for the propagation of internal waves at the interface between two layers of immiscrible fluids of different densities, under the rigid lid assumption, the presence of surface tension and with uneven bottoms. The full (Euler) model for this situation is reduced to a system of evolution equations posed spatially on ℝd, d = 1, 2, which involve two nonlocal operators. The different asymptotic models are obtained by expanding the nonlocal operators and the surface tension term with respect to suitable small parameters that depend variously on the amplitude, wavelengths and depth ratio of the two layers. Furthermore, the consistency of these asymptotic systems with the full Euler equations is established.

Combustion Study of Stabilized Water-in-Diesel Fuel Emulsion

An experimental investigation has been carried out to produce a stable diesel/water emulsion fuel and use it in a diesel engine under different operating and design conditions. The emulsion stayed stable for up to 30% water in diesel for up to one week and 20% water in diesel for four weeks. The physical properties of the stable W/D emulsions in terms of density, surface tension, and viscosity were measured and investigated. The effect of surfactant concentration, mixing time, and mixer speed has been studied. A computer image analyzer system was used to investigate the water droplets-fuel interaction and the water droplets distribution within the diesel phase. The stable emulsion has been used in an indirect injection Ricardo E6 research diesel engine, and performance and engine roughness parameters have been measured. The effect of water/diesel ratio, engine speeds, loads, fuel injection angle, and engine compression ratio on combustion maximum pressure, maximum pressure rise rate, brake power output, and brake-specific fuel consumption has been studied. The addition of water in diesel generally affected the engine combustion noise, brake power output, and specific fuel consumption.

Nanoroughness, Intrinsic Density Profile, and Rigidity of the Air-Water Interface

From large-scale molecular dynamics simulations of the free water surface the capillary wave spectrum is obtained and analyzed in terms of a wave vector dependent surface tension. The bending rigidity is positive but suggested to change sign in the presence of long-range dispersive interactions. Nanoroughness and capillary waves give rise to a scale-dependent density profile that displays minimal broadening at a nanometer scale which defines the intrinsic density profile.

Cauchy problem for viscous rotating shallow water equations

We consider the Cauchy problem for a viscous compressible rotating shallow water system with a third-order surface-tension term involved, derived recently in the modeling of motions for shallow water with free surface in a rotating sub-domain Marche (2007) [19]. The global existence of the solution in the space of Besov type is shown for initial data close to a constant equilibrium state away from the vacuum. Unlike the previous analysis about the compressible fluid model without Coriolis forces, see for instance Danchin (2000) [10], Haspot (2009) [16], the rotating effect causes a coupling between two parts of Hodge's decomposition of the velocity vector field, and additional regularity is required in order to carry out the Friedrichs' regularization and compactness arguments.

Multirange multi-relaxation time Shan–Chen model with extended equilibrium

The work presents simulations with the multirange Shan–Chen model developed by Sbragaglia et al. (2007) [18] , which improved the Shan–Chen model for the proper surface tension term. Also, by introducing the matrix collision operator and extended equilibrium density distribution function, the density ratio is increased from 100 to 160. The Multi-Relaxation Time (MRT) method attracted the attention of researchers due to several advantages, such as better stability, simulations with Prandtl number different from unity, and possibilities to improve the accuracy of the scheme compared with BGK Single Time Relaxation model. Our recent results have shown that the combination of MRT methods with multiphase flow models can improve the achievable gas–liquid density ratio.

Experimental and theoretical study of the evolution of surface roughness in amorphous silicon films grown by low-temperature plasma-enhanced chemical vapor deposition

Using real-time spectroscopic ellipsometry the evolution of the surface roughness of amorphous silicon thin films grown by low-temperature $(200\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C})$ plasma-enhanced chemical vapor deposition (PECVD) at high process gas pressure (3 mTorr) has been studied as a function of the hydrogen dilution gas-flow ratio ${R}_{H}=[{\text{H}}_{2}]/[{\text{SiH}}_{4}]$ with $15\ensuremath{\le}{R}_{H}\ensuremath{\le}60$. To describe the roughness evolution, we have used a $3\mathrm{D}$ linearized continuum equation which includes a negative surface-tension term to take into account the destabilizing effects of short-range attraction and/or shadowing, as well as a smoothing term corresponding to surface diffusion. Using this model we have obtained very good agreement with experimental results for the evolution of the surface roughness in the case of large dilution ratio. However, our results indicate that for small dilution ratio the surface slopes are significantly larger and as a result additional nonlinear terms need to be included at large thicknesses. Our results also indicate that surface diffusion plays an important role during PECVD film growth while the diffusion rate increases with increasing hydrogen dilution ratio. We also find that the early stages of island nucleation play an important role in determining the subsequent roughness evolution. In particular, the assumption of a large wetting angle $({\ensuremath{\theta}}_{W}\ensuremath{\simeq}90\ifmmode^\circ\else\textdegree\fi{})$ for the $3\mathrm{D}$ islands formed in the initial stages leads to significantly better agreement with experiments than a smaller wetting angle $({\ensuremath{\theta}}_{W}\ensuremath{\simeq}45\ifmmode^\circ\else\textdegree\fi{})$. This is consistent with recent experiments on liquid Si droplets on ${\text{SiO}}_{2}$ [H. Kanai et al., J. Mater. Sci. 42, 9529 (2007)] substrates in which a wetting angle of $90\ifmmode^\circ\else\textdegree\fi{}$ was observed.

Repulsive Fermi gas in a harmonic trap: Ferromagnetism and spin textures

We study ferromagnetism in a repulsively interacting two-component Fermi gas in a harmonic trap. Within a local density approximation, the two components phase-separate beyond a critical interaction strength, with one species having a higher density at the trap center. We discuss several easily observable experimental signatures of this transition. The mean field release energy, its separate kinetic and interaction contributions, as well as the potential energy, all depend on the interaction strength and contain a sharp signature of this transition. In addition, the conversion rate of atoms to molecules, arising from three-body collisions, peaks at an interaction strength just beyond the ferromagnetic transition point. We then go beyond the local density approximation, and derive an energy functional which includes a term that depends on the local magnetization gradient and acts as a `surface tension'. Using this energy functional, we numerically study the energetics of some candidate spin textures which may be stabilized in a harmonic trapping potential at zero net magnetization. We find that a hedgehog state has a lower energy than an `in-out' domain wall state in an isotropic trap. Upon inclusion of trap anisotropy we find that the hedgehog magnetization profile gets distorted due to the surface tension term, this distortion being more apparent for small atom numbers. We estimate that the magnetic dipole interaction does not play a significant role in this system. We consider possible implications for experiments on trapped Li-6 and K-40 gases.

Equilibrium mechanics of monolayered epithelium

In order to fully understand the epithelial mechanics it is essential to integrate different levels of epithelial organization. In this work, we propose a theoretical approach for connecting the macroscopic mechanical properties of a monolayered epithelium to the mechanical properties at the cellular level. The analysis is based on the established mechanical models—at the macroscopic scale the epithelium is described within the mechanics of thin layers, while the cellular level is modeled in terms of the cellular surface (cortical) tension and the intercellular adhesion. The macroscopic elastic energy of the epithelium is linked to the energy of an average epithelial cell. The epithelial equilibrium state is determined by energy minimization and the macroscopic elastic moduli are calculated from deformations around the equilibrium. The results indicate that the epithelial equilibrium state is defined by the ratio between the adhesion strength and the cellular surface tension. The lower and the upper bounds for this ratio are estimated. If the ratio is small, the epithelium is cuboidal, if it is large, the epithelium becomes columnar. Importantly, it is found that the cellular cortical tension and the intercellular adhesion alone cannot produce the flattened squamous epithelium. Any difference in the surface tension between the apical and basal cellular sides bends the epithelium towards the side with the larger surface tension. Interestingly, the analysis shows that the epithelial area expansivity modulus and the shear modulus depend only on the cellular surface tension and not on the intercellular adhesion. The results are presented in a general analytical form, and are thus applicable to a variety of monolayered epithelia, without relying on the specifics of numerical finite-element methods. In addition, by using the standard theoretical tools for multi-laminar systems, the results can be applied to epithelia consisting of layers with different mechanical properties.

Singularity formation in a model for the vortex sheet with surface tension

In a recent analytical study, the author has proved well-posedness of the vortex sheet with surface tension. This work included using a formulation of the problem introduced by Hou, Lowengrub, and Shelley for a numerical study of the same problem. The analytical study required identification of a term in the evolution equations which can be viewed as being responsible for the Kelvin–Helmholtz instability; this term is of lower order than the surface tension term. In the present work, the author introduces a simple model for the vortex sheet with surface tension which maintains the same dispersion relation and the same destabilizing force as in the vortex sheet with surface tension. For the model problem, it is found that finite-time singularities can form when the initial data is taken from a certain class. For the vortex sheet with surface tension, the only observed singularities thus far in numerical work have coincided with self-intersection of the fluid interface. There is no analogue of self-intersection in the model problem, and thus the singularities observed in the present work may well be related to a previously unobserved singularity for the full vortex sheet problem.

Effect of Fatty Acids and Beeswax Addition on Properties of Sodium Caseinate Dispersions and Films

Edible films based on sodium caseinate and different saturated fatty acids, oleic acid, or beeswax were formulated. Film-forming emulsions were characterized in terms of particle size distribution, rheological behavior and surface tension. In order to evaluate the influence of lipids on sodium caseinate matrices, mechanical, optical, and water vapor barrier properties were studied, taking into account the effect of water content and film structure on such properties. Saturated fatty acids affected the film properties in a particular way due to the formation of bilayer structures which limited water vapor permeability, giving rise to nonflexible and more opaque films. Oleic acid and beeswax were less effective as water vapor barriers, although the former imparted more flexibility to the caseinate films and did not reduce the film transparency notably.

Stability Behavior of Water-in-Diesel Fuel Emulsion

The presence of water within diesel fuel in the form of water-in-diesel (W/D) emulsion lowers the pollution level of nitrogen oxides and particulate matter. Emulsion of W/D was prepared by high-speed mixing and gradually adding water into the diesel fuel containing a small amount of emulsified agent. We measured the physical properties of diesel fuel and W/D emulsions with a pycnometer for density, Fann V.G. rotational viscometer (Chandler Engineering, Model 3500, Tulsa, Oklahoma, USA) for viscosity, and a Fisher Surface Tensiomat (Fisher Scientific Co., Model 21, Hampton, New Hampshire, USA) for surface tension. We used a computer image analyzer system to investigate the water droplet fuel interaction and the water droplet distribution within the diesel phase. The results of this study show that the emulsions of 10% and 20% W/D were stabilized for 4 weeks and 10 days, respectively, under the conditions of 0.2% surfactant, 15,000 rpm, and 2 minutes of mixing time. Under the same conditions, the stability period is limited to 5 hours for emulsions with a water concentration higher than 20%. An optimum surfactant concentration of 2% was found for 40% W/D due to the polydispersity behavior of the added surfactant. The water droplet distribution and average diameter were significantly affected by the total number of mixing revolutions. We measured and investigated the physical properties of the stable W/D emulsions in terms of density, surface tension, and viscosity.

Nonlinear Deformations of Bilayer Lipid Membranes

Novel continuum models that describe the equilibrium configurations of planar lipid bilayers will be presented. The models are derived within the nonlinear theory for smectic A liquid crystals proposed by Stewart (IW Stewart 2007 Contin. Mech. Thermodyn. 18:343) in which the usual director and unit layer normal do not always necessarily coincide. The total energy of lipid bilayers consists of an elastic splay term, smectic layer bending and compression terms, a coupling term between the director and layer normal, a surface tension term, and a surface anchoring term. Nonlinear equilibrium equations are obtained by using variational methods and are then solved by analytical and numerical methods. The solutions illustrate the nonlinear deformations of lipid bilayers including the misalignment of lipid molecules at their interface with other media such as, for example, proteins and surface substrates.