Interfacial tension measurements at the interface between two highly immiscible electrolyte solutions: the trapped air bubble method

A dynamic method for the measurement of interfacial tension at a liquid–liquid interface under controlled interfacial potential difference is described. The interface was formed as a drop suspended at the tip of a liquid filled glass micro-syringe into which a trapped air bubble of known volume had been introduced. Changes in volume of the air bubble allow changes in the surface tension to be calculated. Application to measurement of the variation in interfacial tension with cyclic variation in interfacial potential difference (‘cyclic volttensiometry’) is demonstrated.     

A Study of Dynamic Interfacial Properties as Related to Foaming Properties of Sodium 2,5-dialkyl Benzene Sulfonates

In this article, foaming properties and dynamic interfacial properties of a series of sodium 2,5-dialkyl benzene sulfonates in aqueous solutions were carried out to elucidate the relationship between foaming properties and dynamic interfacial properties. The properties of foams generated from bubbling air through different surfactant solutions were measured using a modified Bikerman device. The dynamic surface tension and surface dilational elasticity were obtained from an image analysis technique based on the oscillating bubble method. The surfactants molecular adsorption at the air/water interface was introduced with Rosen empirical equation and the rate of adsorption was determined from measurements of the dynamic surface tension. The surfactant with the longest alkyl chain shows the lowest dynamic surface activity, which lead to the lowest foam volume. The short ortho straight alkyl chain has little effect on the arrangement of molecules at the interface and the foam stability changes a little with the changing of the ortho alkyl chain length. The foam stability is correlated with both the higher surface dilational elasticity and the larger surface monolayer strength.     

Spreading of a fluid phase on a spherical surface

The adsorption between a liquid drop and a micro-particle in an air or an air bubble and a micro-particle in water is dominated by liquid-solid or air-solid interfacial tension and wetting area of the liquid or air on the particle surface. The wetting area is determined by the spreading of the liquid drop or the bubble on the micro-particle. To explore this spreading, a wetting model of a fluid phase on a spherical particle was built. According to the theoretical results, the contact angle is constant when a fluid phase spreads on a spherical solid surface; the micro-particle can not submerge under a fluid when only interfacial tensions are involved and the wetting is not a complete wetting. The corresponding experiments were performed to confirm the theoretical results.     

探针型表面张力测试技术的应用研究进展

表面张力是流体重要的物理性质,测定液体表面张力的方法通常包括毛细管上升法、最大气泡压力法、吊环法/吊片法、滴重法/滴体积法、旋滴法和悬滴法。本文综述了测定界面处表(界)面张力和表面压力的方法,详细介绍了基于最大拉力法(Whilhemy吊片法)改进的表面张力测试技术(Du Noüy-Padday),并且概述了这一技术近些年在生物研究、药物研发以及环境监测等领域方面的最新应用。     

Static and Dynamic Wetting Behavior of Triglycerides on Solid Surfaces

Triglyceride wetting properties on solid surfaces of different hydro-phobicities were investigated using three different methods, namely, the sessile drop method for static contact angle measurements, the Wilhelmy method for dynamic contact angle measurements, and the captive bubble method to investigate thin triglyceride film stability. For solid surfaces having a surface free energy higher than the surface tension of triglycerides (tributyrin, tricaprylin, and triolein), a qualitative correlation was observed between wetting and solid/triglyceride relative hydrophobicities. On surfaces presenting extreme hydrophobic or hydrophilic properties, medium-chain triglycerides had a behavior similar to that of long-chain unsaturated ones. On a high-energy surface (glass), tricaprylin showed an autophobic effect subsequent to molecular adsorption in trident conformation on the solid, observed with the three methods. Thin triglyceride films between an air bubble and a solid surface were stable for a short time, for solids with a surface free energy larger than the triglyceride surface tension. If the solid surface had a lower surface free energy, the thin film collapsed after a time interval which increased with triglyceride viscosity. Copyright 2000 Academic Press.     

Effect of Alkyl Chain Length on the Interfacial Dilational Properties of Hydroxy-Substituted Alkyl Benzenesulfonates

Dilational rheological behaviors of adsorption layers of three surfactants, sodium 2-hydroxy-3,5-dioctyl benzene sulfonate (C₈C₈), sodium 2-hydroxy-3-octyl-5-decyl benzene sulfonate (C₈C₁₀), and sodium 2-hydroxy-3-octyl-5-dodecylbenzenesulfonate (C₈C₁₂) formed at air–water and decane–water interfaces, have been investigated as a function of concentration and frequency (0.002–0.1 Hz) by the oscillating bubble/drop method. The experimental results show that the dilational moduli of hydroxy-substituted alkyl benzenesulfonates are obviously higher than those of the common surfactants, because the interfacial interactions between alkyl chains are improved drastically by the unique arrangement of C₈C₈ molecules at the interface. However, the moduli at the decane–water interface are much lower than those at the surfaces because decane molecules will insert into the surfactant molecules adsorbed at the interface and destroy the interactions between alkyl chains. With an increase in the number of carbon atom of 5-alkyl, the surface dilational modulus decreases because the orientation of the surfactant molecules at the surface varies from parallel to tilt. On the other hand, the diffusion-exchange process dominates the interfacial behavior and the interfacial modulus improves with the increase in the length of the alkyl chain.     

Adsorption Kinetics of Alkyl Polyglucoside at the Air—Solution Interface

The air-solution equilibrium tension γe and dynamic surface tension γt,of nonionic surfactant alkyl polyglucoside have been studied. γe was measured by the Wilhelmy method with Rruess K12 tensiometer. The CMC and the surface excesses T were determined from the surface tension vs. concentration curve. The γt decays were measured in the range 0.2-20s using a maximum bubble pressure instrument and analyzed with the Ward and Tordai equation.     

On the dissolution of vapors and gases

The captive bubble technique in combination with axisymmetric drop shape analysis (ADSA-CB) and with micro gas chromatography is used to study the dynamics of dissolution of different gases and vapors in water in situ. The technique yields the changes in the interfacial tension and bubble volume and surface. As examples, the dissolution of methanol and hexane vapors, inhaled anesthetic vapors, and gases, that is, diethyl ether, chloroform, isoflurane, enflurane, sevoflurane, desflurane, N2O, and xenon, and as nonimmobilizers perfluoropentane and 1,1,2-trichloro-1,2,2-trifluoro-ethane (R113) were investigated. The examination of interfacial tension-time and bubble volume-time functions permits us to distinguish between water-soluble and -insoluble substances, gases, and vapors. Vapors and gases generally differ in terms of the strength of their intermolecular interactions. The main difference between dissolution processes of gases and vapors is that, during the entire process of gas dissolution, no surface tension change occurs. In contrast, during vapor dissolution the surface tension drops immediately and decreases continuously until it reaches the equilibrium surface tension of water at the end of dissolution. The results of this study show that it is possible to discriminate anesthetic vapors from anesthetic gases and nonimmobilizers by comparing their dissolution dynamics. The nonimmobilizers have extremely low or no solubility in water and change the surface tension only negligibly. By use of newly defined molecular dissolution/diffusion coefficients, a simple model for the determination of partition coefficients is developed.     

The effect of the partial pressure of water vapor on the surface tension of the liquid water-air interface

Precise measurements of the surface tension of water in air vs. humidity at 5, 10, 15, and 20 °C are shown. For constant temperature, surface tension decreases linearly for increasing humidity in air. These experimental data are in good agreement with a simple model based on Newton's laws here proposed. It is assumed that evaporating molecules of water are ejected from liquid to gas with a mean normal component of the speed of "ejection" greater than zero. A high humidity in the air reduces the net flow of evaporating water molecules lowering the effective surface tension on the drop. Therefore, just steam in air acts as an effective surfactant for the water-air interface. It can partially substitute chemical surfactants helping to reduce their environmental impact.     

Adsorption of Alkyltrimethylammonium Bromides at the Various Interfaces

The adsorption of alkyltrimethylammonium bromide homologues has been studied at oil/water and air/water interfaces. Dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, and hexadecyltrimethylammomium bromide were used. As an oil phase the aliphatic hydrocarbons of the same chain length as that of surfactants molecules were used. The interfacial tension was measured by the drop volume method and the equilibrium values were received. The surface tension was measured by the drop weight method. The values of surface excess Gamma were calculated from the Gibbs equation. The experimental results were tested by the Langmuir isotherm as well as by the isotherm developed by E. Blomgren and J. O'M. Bockris (J. Phys. Chem. 63, 1475 (1959)). Copyright 2000 Academic Press.     

Effect of amino acids on aggregation behaviors of sodium deoxycholate at air/water surface: surface tension and oscillating bubble studies

The aggregation behaviors of sodium deoxycholate (NaDC) at the air/water surface were investigated via surface tension and oscillating bubble measurements in the absence and presence of three alkaline amino acids, namely, L-Lysine (L-Lys), L-Arginine (L-Arg), and L-Histidine (L-His). The results of surface tension measurements show that NaDC has a lower ability to reduce the surface tension of water, because NaDC molecules orient at the surface in an oblique direction and tend to aggregate together, which is approved by molecular dynamics (MD) simulation. L-Lys is the most efficient of the three amino acids in reducing the critical aggregation concentration (cac) of NaDC in aqueous solution. The influence of amino acids on the dilational rheological properties of NaDC was studied using the drop shape analysis method in the frequency range from 0.02 to 0.5 Hz. The results reveal that the absolute modulus passes through a maximum value with increasing NaDC concentration. The addition of amino acids increases the absolute modulus of NaDC, and the maximum value is observed at much lower concentration. From the perspective of structures of amino acids, the performance of L-Arg is similar to that of L-His, and both of them bring out a smaller effect on the absolute modulus than that of L-Lys. From the above results, it may be presumed that electrostatic and hydrophobic effects are important impetus during the interaction between amino acids and NaDC at the air/water surface. Hydrogen bonding is so ubiquitous in the system that the difference of hydrogen bonding between NaDC and amino acid is ignored.     

Effect of compressed bovine lipid extract surfactant films on oxygen transfer

In the lungs, oxygen transfer from the inspired air to the capillary blood needs to cross the surfactant lining layer of the alveoli. Therefore, the gas transfer characteristics of lung surfactant film are of fundamental physiological interest. However, previous in vitro studies-most relied on the Langmuir-type balance-fail to cover the low surface tension range (i.e., less than the equilibrium surface tension of approximately 25 mJ/m2) due to film leakage. We have recently developed a novel in vitro experimental strategy, the combination of axisymmetric drop shape analysis and captive bubble technique (ADSA-CB), in studying the effect of surfactant films on interfacial gas transfer (Langmuir 2005, 21, 5446). In the present work, ADSA-CB is used as a micro-film-balance to study the effect of compressed bovine lipid extract surfactant (BLES) films on oxygen transfer. A low surface tension ranging from approximately 25 mJ/m2 to 2 mJ/m2 is studied. The experimental results suggest that lung surfactant films at a low surface tension near 2 mJ/m2 provide resistance to oxygen transfer, as indicated by a decrease of 30-50% in the mass transfer coefficient (kL) of oxygen in BLES suspensions with respect to water. At higher surface tension (i.e., >6 mJ/m2), the resistance to oxygen transfer is only modest, i.e., the decrease in kL is less than 20% compared to water. The experimental results suggest that lung surfactant plays a role in oxygen transfer in the pulmonary system.     

Understanding (sessile/constrained) bubble and drop oscillations

The diffuse literature on drop oscillation is reviewed, with an emphasis on capillary wave oscillations of constrained drops. Based on the review, a unifying conceptual framework is presented for drop and bubble oscillations, which considers free and constrained drops/bubbles, oscillation of the surface or the bulk (i.e. center of mass) of the drop/bubble, as well as different types of restoring forces (surface tension, gravity, electromagnetic, etc). Experimental results (both from literature and from a new set of experiments studying sessile drops in cross flowing air) are used to test mathematical models from literature, using a novel whole profile analysis technique for the new experiments. The cause of oscillation (cross flowing air, vibrated surface, etc.) is seen not to affect oscillation frequency. In terms of models, simplified models are seen to poorly predict oscillation frequencies. The most advanced literature models are found to be relatively accurate at predicting frequency. However it is seen that no existing models are reliably accurate across a wide range of contact angles, indicating the need for advanced models/empirical relations especially for drops undergoing the lowest frequency mode of oscillation (the order 1 degree 1 non-axisymmetric ‘bending’ mode that corresponds to a lateral ‘rocking’ motion of the drop).     

Effect of water hardness on surface tension and dilational visco-elasticity of sodium dodecyl sulphate solutions

The complementary drop and bubble profile analysis and maximum bubble pressure tensiometry are used to measure the dynamic surface tension of aqueous SDS solutions in the presence of hardness salts (CaCl(2) and MgCl(2) in the ratio of 2:1 at concentrations of 6 and 40FH). The presence of hardness salts results in an essential increase of the SDS adsorption activity, which indicates the formation of Ca(DS)(2) and Mg(DS)(2) in the SDS solutions. The surface tension isotherms of SDS in presence of Ca(DS)(2) and Mg(DS)(2) are described using the generalised Frumkin model. The presence of hardness salts accelerates the ageing of SDS solutions as compared with the addition of 0.01 M NaCl due to a faster hydrolysis and hence formation of dodecanol. These results are used to estimate the possible concentration of dodecanol in the studied SDS solutions. The buoyant bubble profile method with harmonic surface oscillations is used to measure the dilational rheology of SDS solutions in presence of hardness salts in the frequency range between 0.005 Hz and 0.2 Hz. The visco-elasticity modulus in the presence of hardness salts is higher as compared with its values in the presence of 0.01 M NaCl additions. The ageing of SDS solutions leads to an essential increase of the visco-elastic modulus.     

Influence of alkyl chain length of alpha olefin sulfonates on surface and interfacial properties

Alpha olefin sulfonates (AOS) with various alkyl chain lengths have been used to investigate the influence of alkyl chain length on the interfacial properties at air–water, liquid paraffin–water, and parafilm–water interfaces. It was found that the critical micelle concentration decreased with increasing alkyl chain length, while the efficiency of reducing surface tension was inverse relationship with alkyl chain length. The diffusion coefficient obviously reduced with an increase of surfactant concentration and alkyl chain length. The C_14-16AOS shows better wettability and emulsification than C_16-18AOS and C_20-24AOS. For foaming properties, the foamability and foam stability dramatically decreased with increasing alkyl chain length.     

Surface and micelle properties of novel multi-dentate surfactants

Novel multi-dentate surfactants, based on alkyl amines of varying hydrophobicity were synthesized, and molecular structures were characterized by IR, UV-vis, NMR and FAB-MS. The new surfactants have good water solubility and are highly efficient at reducing aqueous surface tension. Small-angle neutron scattering (SANS) studies were carried out with aqueous solutions in D(2)O to study aggregation. Spherical micelles were shown to form, and these grow with increasing alkyl chain length; their conformation is unusual compared to conventional linear chain surfactants.     

Behaviour of trimethyl-n-propyl-and tetra-n-pentyl-ammonium ions at a mercury electrode

Measurements of the interfacial tension, using a drop time technique, have been made for trimethyl-n-propyl- and tetra-n-pentylammonium bromide solutions at different temperatures and concentrations. The results thus obtained show that the curves for the surface excess of concentration and the global surface excess of entropy are very different for the two cations studied. These results can be interpreted as indicating the role of hydrophobic forces between the water molecules and the alkyl groups when these contain more than three carbon atoms in a chain.     

Effect of solution viscosity on dynamic surface tension detection

A dynamic surface tension detector (DSTD) was used to examine the molecular diffusion and surface adsorption characteristics of surface-active analytes as a function of solution viscosity. Dynamic surface tension is determined by measuring the differential pressure across the air/liquid interface of repeatedly growing and detaching drops. Continuous surface tension measurement throughout the entire drop growth is achieved for each eluting drop (at a rate of 30 drops/min for 2 μl drops), providing insight into the kinetic behavior of molecular diffusion and orientation processes at the air/liquid interface. Three-dimensional data are obtained through a calibration procedure previously developed, but extended herein for viscous solutions, with surface tension first converted to surface pressure, which is plotted as a function of elution time axis versus drop time axis. Thus, an analyte that lowers the surface tension results in an increase in surface pressure. The calibration procedure derived for the pressure-based DSTD was successfully extended and implemented in this report to experimentally determine standard surface pressures in solutions of varied viscosity. Analysis of analytes in viscous solution was performed at low analyte concentration, where the observed analyte surface activity indicates that the surface concentration is at or near equilibrium when in a water mobile phase (viscosity of 1.0 Cp). Two surface-active analytes, sodium dodecyl sulfate (SDS) and polyethylene glycol (MW 1470 g/mol, PEG 1470), were analyzed in solutions ranging from 0 to 60% (v/v) glycerol in water, corresponding to a viscosity range of 1.0-15.0 Cp. Finally, the diffusion-limited surface activity of SDS and PEG 1470 were observed in viscous solution, whereby an increase in viscosity resulted in a decreased surface pressure early in drop growth. The dynamic surface pressure results reported for SDS and PEG 1470 are found to correlate with solution viscosity and analyte diffusion coefficient via the Stokes-Einstein equation.     

Aggregation behavior of pyridinium based ionic liquids in water--surface tension, 1H NMR chemical shifts, SANS and SAXS measurements

The aggregation behavior of short alkyl chain ionic liquids (ILs), namely 1-butyl, or 1-hexyl or 1-octylpyridinium and 1-octyl-2-, or -3-, or -4-methylpyridinium chlorides, in water has been assessed using surface tension, electrical conductance, (1)H NMR, small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) measurements. Critical aggregation concentrations (CACs), adsorption (at air/water interface) and thermodynamic parameters of aggregation have been reported. The values of CAC and area per adsorbed molecule decrease with the number of carbon atoms in the alkyl chain. The aggregation process is driven by both favorable enthalpy and entropy contributions. An attempt was made to examine the morphological features of the aggregates in water using SANS and SAXS methods. SANS and SAXS curves displayed diffuse structural peaks that could not be model fitted, and therefore, we calculated the mean aggregation numbers from the Q(max) assuming that IL molecules typically order into cubic type clusters.