Effect of counterions on surface and foaming properties of dodecyl sulfate

The influence of counterions of surfactant on interfacial properties is studied by measuring foamability, foam stability, equilibrium and dynamic surface tension, and surface viscosity. The surfactant chosen is anionic dodecyl sulfate with various counterions, Li(+), Na(+), Cs(+), and Mg(++). Surface tension measurements show a decrease in the following order: LiDS > NaDS > CsDS > Mg(DS)(2). Foamability done using shaking method shows similar order as surface tension, i.e., LiDS > NaDS > CsDS > Mg(DS)(2). This has been explained in terms of the differences in micellar stability and diffusion of monomers. This is further confirmed by our dynamic surface tension results, which show the same order as equilibrium surface tension (i.e., LiDS > NaDS > CsDS > Mg(DS)(2)) at low bubble frequencies but the order is LiDS > NaDS = Mg(DS)(2) > CsDS at high bubble frequencies. Foam stability measurements were done at concentrations below and above cmc to elucidate the role of micelles. It was found that there is no significant change in foam stability when counterions are changed for surfactant concentration values below the cmc, but at concentration above cmc the foam stability of CsDS and Mg(DS)(2) are much greater than LiDS and NaDS indicating presence of stable micelles are essential to high foam stabilities. Surface viscosity measurements correlated well with the foam stability trends and gave the following order LiDS < NaDS < CsDS < Mg(DS)(2), indicating that the molecules of CsDS and Mg(DS)(2) are tightly packed at the air/water interface.     

Adsorption of sodium dodecyl sulfate onto clathrate hydrates in the presence of salt

This work presents the effect of NaCl on the adsorption of sodium dodecyl sulfate (SDS) at the cyclopentane (CP) hydrate-water interface. The adsorption isotherms and the SDS solubility in NaCl solutions are obtained using liquid-liquid titrations. The solubility data are determined at typical hydrate forming temperatures (274-287K) to ensure that the adsorption isotherms are obtained within SDS solubility limits in NaCl solutions. The isotherms show L-S (Langmuir-Step) type behaviors with 1mM and 10mM NaCl solutions while L type isotherm is determined for 25mM NaCl solutions due to the low SDS solubility in this salt concentration. Zeta potentials of CP hydrate particles in the aqueous solutions support the shape of the adsorption isotherm with the 1mM NaCl solution. The 1mM NaCl case shows the highest SDS adsorption amount among the cases with 0mM, 10mM, and 25mM NaCl solutions. In this case, the competition for adsorption between Cl(-) and DS(-) is not as strong compared to the 10 and 25mM NaCl cases and the presence of Na(+) ions may reduce the repulsion between DS(-) ions, which results in a higher adsorption of DS(-) ions and enhanced enclathration.     

Effects of electrolyte and nonelectrolyte additives on adsorption and surface rheological characteristics of humic acid salt solutions

The du Noüy and oscillating droplet shape methods are employed to study the effects of the ionic strength and pH of a medium, as well as the addition of nonelectrolytes (lower alcohols and acetone), on the adsorption and surface rheological characteristics of aqueous solutions of humic acid salts (sodium humates) at the liquid-air interface. When added in concentrations at which the aggregation of humic substances is not yet observed, strong electrolytes (NaCl and HCl) decrease the equilibrium surface tension and increase the dilatational viscoelastic modulus of aqueous sodium humate solutions. The aggregation of humic substances enhances the surface tension and reduces the viscoelastic modulus of surface layers. Nonelectrolyte additives decrease the surface tension and dilatational modulus of aqueous humic acid salt solutions. The equilibrium surface tension of sodium humate-nonelectrolyte mixed solutions is described in terms of two different models, namely, a relatively exact model of polyelectrolyte-nonionic surfactant adsorption and a simple additive model. It is shown that the additive model may be used to predict the equilibrium surface tension for the mixtures of high- and low-molecular-mass surfactants.     

Effect of the electrolyte concentration on cation binding in aqueous surfactant solutions.

Electrospray ionisation mass spectrometry (ESI-MS) is used for the qualitative and quantitative study of ion binding to interfaces. The ESI-MS measurements are carried out in aqueous solutions of sodium dodecyl sulphate (SDS) in the presence of NaCl, NH(4)ClO(4) , KCl, or Mg(ClO(4))(2) . The effect of the electrolyte concentration on the fractions, y(cation(+) ), of the DS(-) monomers bound to the cations is shown. Moreover, the binding stability of different cations with DS(-) monomers is determined versus the electrolyte concentration. This stability and the y(Na(+) ) values (the Na(+) ions derived from SDS), estimated in the presence of a given electrolyte, are quantitatively correlated with the electrolyte cation effect on the water structure. We also present calibration curves from which the molar concentrations of the sodium ions (derived from SDS) and of the other cations (derived from the electrolyte), bound to the SDS-micelle surface at a given electrolyte concentration, can be obtained. Besides, specific ion effects (Hofmeister effects) are considered for 1:1 electrolytes.     

Interfacial interactions between amphiphilic cyclodextrins and physiologically relevant cations

The compression isotherms of a series of amphiphilic cyclodextrins, formed (a) by acylation at the secondary hydroxyl face and (b) by acylation accompanied by varying degrees of sulfatation (DS) at the primary hydroxyl face (DS=0, 4, and 7), have been studied on subphases of pure water and of water containing NaCl, KCl, MgCl(2), and CaCl(2) at inter- and extracellular concentrations. The formation of solid lipid nanoparticles (SLNs) by two of the molecules has been observed, while these do not aggregate at concentrations of monovalent salts up to 150 mM for the sulfated derivative. In the presence of divalent salts one of these with a DS=0 for sulfatation degree flocculates at divalent salt concentrations below 0.1 mM while the other with a DS=4 flocculates at Mg(2+) concentration above 5 mM and a Ca(2+) concentration above 3 mM. AFM noncontact mode imaging has been carried out, in air, for the SLNs deposited on mica.     

十二烷基硫酸钠水溶液的动态表面吸附性质

利用MPTC型气泡压力张仪研究了十二烷基硫酸钠(SDS)溶液在不同NaCl 浓度下的动态表面吸附性质, 分析了离子型表面活性剂在表面吸附层和胶束中形成双电层结构产生表面电荷对动态表面扩散过程和胶束性质的影响. 结果表明, SDS在表面吸附过程中, 表面电荷的存在会产生5.5 kJ·mol^-1的吸附势垒(E_a), 显著降低十二烷基硫酸根离子(DS^-)的有效扩散系数(D_eff). 十二烷基硫酸根离子的有效扩散系数与自扩散系数(D)的比值(D_eff/D)仅为0.013, 这表明SDS与非离子型表面活性剂不同, 在吸附初期为混合动力控制吸附机制. 加入NaCl可以降低吸附势垒. 当加入不小于80 mmol·L^-1 NaCl后, E_a小于0.3 kJ·mol^-1, D_eff/D在0.8-1.2之间, 表现出与非离子型表面活性剂相同的扩散控制吸附机制. 同时, 通过分析SDS胶束溶液的动态表面张力获得了表征胶束解体速度的常数(k₂). 发现随着NaCl 浓度的增大, k₂减小, 表明SDS胶束表面电荷的存在会增加十二烷基硫酸根离子间的排斥力, 促进胶束解体.     

SDS及其与十二烷基三乙基溴化铵混合体系在矿化水中的表面活性

测定了十二烷基硫酸钠(SDS)、十二烷基三乙基溴化铵(DTEAB)单一体系及不同摩尔比的混合体系在矿化水溶液中的表面活性,并与在纯水和NaCl水溶液中的表面活性作了比较．所得结果表明：(1)阴离子表面活性剂SDS在含Ca^2 ,Mg^2 等的矿化水中有比在纯水和NaCl水溶液中更好的表面活性．这一方面是由于矿化水中的Ca^2 ,Mg^2 对负电胶团和表面吸附层的强烈电性作用,另一方面在大量Na^ 存在时,钠钙盐混合表面活性剂Krafft点提高不多;(2)SDS和DTEAB混合物在矿化水中具有很强的增效作用,其表面活性的变化规律与在纯水和NaCl水溶液中基本相同,表明阴阳离子表面活性剂混合体系具有优异的抗矿化水性能．这些结果可用阴、阳表面活性离子的电性作用解释．     

Surface rheology and foaming properties of sodium oleate and C12(EO)6 aqueous solutions

The dynamic surface tension (DST) and the surface viscoelastic modulus of sodium oleate aqueous solutions at different concentrations were measured using an image analysis tensiometer based on the oscillating bubble technique. The diffusion coefficient of oleate moieties was calculated from DST measurements and the surface viscoelastic modulus using the Langmuir-Szyszkowski and the diffusion-controlled adsorption models. The viscoelastic moduli obtained from model calculations were compared with the corresponding experimental values. The diffusion coefficient of C(12)(EO)(6) in water and the parameters of the Langmuir-Szyszkowski adsorption isotherm were taken from the literature and used to calculate the surface viscoelastic modulus of its aqueous solutions at different concentrations. The foaming properties of both C(12)(EO)(6) and sodium oleate solutions, viz., the foam conductance and the water volume fraction in the foam, were measured using a commercial Foamscan device. Foaming experiments with C(12)(EO)(6) and sodium oleate solutions were carried out either under static conditions; i.e., the foam conductance and the water volume fraction were measured as a function of time after the generation of a fixed volume of foam, or under dynamic conditions; i.e., the foam conductance and the water volume fraction were measured during foam formation. The variations in the foam permeability as a function of surfactant concentration were related to the viscoelastic properties of the air/water interface and to the presence of micelles in the foam films. With foams in which the water volume fraction was higher than 0.05, the foam electrical conduction could be described using a simple parallel resistor model and their conductance measurements were related to the foam water volume fraction. The results related to water drainage under static conditions were used to interpret water drainage under dynamic conditions. Preliminary conjectures on the influence of foam permeability and water volume fraction on the yield of the flotation deinking process were drawn from these results.     

Effects of atmospherically important solvated ions on organic acid adsorption at the surface of aqueous solutions

The effects of salts on the solubility of amphiphilic organic molecules are of importance to numerous atmospheric, environmental, and biological systems. A detailed picture of the influence of dissolved atmospheric salts, NaCl and Na(2)SO(4), on the adsorption of hexanoic acid at the vapor/water interface is developed using vibrational sum-frequency spectroscopy and surface tension measurements as a function of time, organic concentration, and solution pH. We have found that for hexanoic acid adsorption at the vapor/water interface, a fast initial adsorption is followed by two considerably slower processes: a reorientation of the polar headgroup and a restructuring of the headgroup solvation shell. The addition of salts affects this restructuring by reducing the range of water--headgroup interactions immediately upon surface adsorption for ion containing solutions. Reorientation of the organic headgroup with time occurs at the surface of both salt-containing and salt-free solutions, but the most stable orientation differs with the added ions. The dissolved salts also enhance the interfacial concentration of hexanoic acid, consistent with the known salting-out behavior of Cl(-) and SO(4)(2-) anions.     

Propensity for the air/water interface and ion pairing in magnesium acetate vs magnesium nitrate solutions: molecular dynamics simulations and surface tension measurements

Molecular dynamics simulations in slab geometry and surface tension measurements were performed for aqueous solutions of magnesium acetate and magnesium nitrate at various concentrations. The simulations reveal a strong affinity of acetate anions for the surface, while nitrate exhibits only a very weak surface propensity, and magnesium is per se strongly repelled from the air/water interface. CH3COO- also exhibits a much stronger tendency than NO3- for ion pairing with Mg2+ in the bulk and particularly in the interfacial layer. The different interfacial behavior of the two anions is reflected by the opposite concentration dependence (beyond 0.5 M) of surface tension of the corresponding magnesium salts. Measurements, supported by simulations, show that the surface tension of Mg(NO3)2(aq) increases with concentration as for other inorganic salts. However, in the case of Mg(OAc)2(aq) the surface tension isotherm exhibits a turnover around 0.5 M, after which it starts to decrease, indicating a positive net solute excess in the interfacial layer at higher concentrations.     

Effect of different salts and detergents on luciferin-luciferase luminescence of the enchytraeid Fridericia heliota

The study addresses the effect produced by different inorganic salts and detergents (SDS, Triton X-100, the Tween series) on the ATP-dependent bioluminescent reaction catalyzed by the luciferase of the new earthworm species Fridericia heliota (Annelida: Clitellata: Oligochaeta: Enchytraeidae). It has been shown that the effect of divalent metal salts on luminescence is determined by the action of cations. Three of them - Mg(2+), Mn(2+) and Ca(2+) - can stimulate luciferase activity at concentrations varying within a wide range, and Mn(2+) can act as a 100%-effective substitute for Mg(2+) in F. heliota luminescence reaction in vitro. The inhibitory effect of monovalent metal salts on luminescence is largely determined by the action of the anion part of the molecule. The effectiveness of the inhibitory effect of anions increases in the following order: Cl(-)相似文献   

Synergy between Hofmeister effect and coupled water in proteins: Unusual dilational moduli of BSA at air/solution interface

This study relates interfacial interactions of bovine serum albumin (BSA) molecules in dilute solutions with its dilatational rheology. Dynamic surface tension and the associated dilational elastic modulus and viscosity for BSA and mixtures of BSA with Hofmeister electrolytes—NaCl, NaClO₄, Na₂SO₄, NaF and Na₂HPO₄ have been studied using a sinusoidal surface compression and expansion for frequencies ranging from 0.01 to 0.4 Hz. at solution/air interface. In all the BSA + electrolyte systems, both the elastic modulus and viscosity show unusually high values compared with pure BSA or pure electrolytes. In the presence of NaF and Na₂SO₄ the viscosity of protein increases almost by 50–80-fold and the corresponding elastic modulus also changes by 30–50-fold. Hydrated Hofmeister ions surely influence the measured rheological properties. In addition, the synergistic effect of the hydrated protein and the vicinal hydrated electrolytes possibly contribute to the high viscosity and elasticity due to change in dynamics of these assemblies. Thus the behavior of BSA is effected by salts in different ways, especially due to the dynamics and strength of the water molecules in the assembly.     

The effect of triethylenetetraamine (Trien) on the ion flotation of Cu(2+) and Ni(2+)

Ion flotation is a separation process involving the adsorption of a surfactant and counterions at an air/aqueous solution interface. It shows promise for removing toxic heavy metal ions from dilute aqueous solutions. Here we report the effect of a neutral chelating ligand, triethylenetetraamine (Trien), on the ion flotation of cations with dodecylsulfate, DS(-), introduced as sodium dodecylsulfate, SDS. Ion flotation in the aqueous SD-Cu(II)-Ca(II)-Trien system gave strongly preferential removal of Cu(II) over Ca(II), which is a reversal of the order of selectivity seen in the SDS-Cu(II)-Ca(II) system containing no Trien. The removal rates of Cu(2+) and Ni(2+) with DS(-) were much faster in the presence of Trien than for simple aquo ions, and the final metal concentration was significantly lower. Surface tension measurements showed that Trien enhanced the surface activity and adsorption density for SDS-Cu(II) and SDS-Ni(II) solutions. The overall change in the Gibbs free energy for adsorption resulting from complexation was -3.60 kJ/mol for Cu(II) and -3.50 kJ/mol for Ni(II). This included the effects of hydrophobic interactions between the metal-Trien complexes at the air/solution interface, along with changes in the amount of dehydration associated with cosorption of the metal-Trien complex with DS(-) at the air/solution interface.     

咪唑基表面活性离子液体在气/液界面的扩张粘弹性

合成了两种咪唑基表面活性离子液体,通过界面膨胀流变法研究了其在气/液界面的聚集行为,考察了咪唑基表面活性离子液体浓度、无机盐和温度对聚集行为的影响。研究发现,咪唑基表面活性离子液体在吸附过程中吸附控制占主导作用,而弛豫过程不是单一指数函数;加入无机盐或升高温度可以提高咪唑基表面活性离子液体的表面活性、增强其在界面的吸附能力、降低表面张力。扩张流变结果显示扩张模量、弹性模量和粘性模量随震荡频率增加而增加;随表面活性离子液体浓度增大,扩张模量先增大后减小。扩张模量随温度升高或无机盐(NaBr或CaBr₂)的加入而降低。表面活性离子液在气/液界面形成的吸附膜以弹性模量为主,而且C₁₄mimBr的界面膜弹性模量大于C₁₂mimBr的界面膜弹性模量。     

Interface tension of silica hydroxylated nanoparticle with brine: a combined experimental and molecular dynamics study

We have used molecular dynamics simulations to calculate the interfacial tension of hydroxylated SiO(2) nanoparticles under different temperatures and solutions (helium and brine with monovalent and divalent salts). In order to benchmark the atomistic model, quartz SiO(2) interfacial tension was measured based on inverse gas chromatography under He atmosphere. The experimental interfacial tension values for quartz were found between 0.512 and 0.617 N/m. Our calculated results for the interfacial tension of silica nanoparticles within helium atmosphere was 0.676 N/m, which is higher than the value found for the system containing He∕α-quartz (0.478 N/m), but it is similar to the one found for amorphous silica surface. We have also studied the interfacial tension of the nanoparticles in electrolyte aqueous solution for different types and salts concentrations (NaCl, CaCl(2), and MgCl(2)). Our calculations indicate that adsorption properties and salt solutions greatly influence the interfacial tension in an order of CaCl(2) > MgCl(2) > NaCl. This effect is due to the difference in distribution of ions in solution, which modifies the hydration and electrostatic potential of those ions near the nanoparticle.     

Surface Viscoelasticity of Concentrated Salt Solutions: Specific Ion Effects

Herein, we study the viscoelastic response of concentrated salt solutions using surface waves excited by electrocapillarity. We show that the hydrodynamic behaviour of the solutions is similar to that of water at concentrations up to 2 m— well above the concentration C*, at which inhibition of bubble coalescence occurs in these solutions. This result excludes the occurrence of changes in the slip conditions at C*, postulated to explain this inhibition. Our study is carried out on salts that both increase and decrease the surface tension. We observe that the salt that decreases the tension does not change the surface behaviour at all, whereas the other two salts essentially produce negative contributions to the surface viscoelasticity at very high salt concentrations. The effects observed are quite large and remain to be explained.     

Rheological surface properties of C12DMPO solution as obtained from amplitude- and phase-frequency characteristics of an oscillating bubble system

The experimental data on the surface rheological characteristics of dodecyl dimethyl phosphine oxide solutions obtained in a fully automatic oscillating bubble device under microgravity conditions in the frequency range 0.01-100 Hz are presented. The complex surface elasticity modulus is obtained form the amplitude- and phase-frequency characteristics of established pressure oscillations in a closed cell without calibration experiments by direct calculation of the necessary coefficients. The characteristics of the adsorption layers obtained from the elasticity modulus are in good agreement with adsorption isotherms and equations of state accounting for the intrinsic (2D) monolayer compressibility.     

Adsorption and rheological characteristics of humic acid salts at liquid-gas interfaces

Du Noöy ring and oscillating droplet methods are used to study the adsorption and dilatation rheological characteristics (viscoelastic modulus and phase angle) of aqueous solutions of humic acid salts at liquid-gas interfaces. It is established that the equilibrium surface tension and limiting surface elasticity of humic acid salt solutions are in good agreement with the model of a real two-dimensional solution that was previously proposed for biopolymers. Based on the results of analyzing dynamic surface tension and adsorption kinetics, it is shown that humic acid salts are characterized by a nondiffusion (barrier) adsorption mechanism.     

Control of Ostwald ripening by using surfactants with high surface modulus

We describe results from systematic measurements of the rate of bubble Ostwald ripening in foams with air volume fraction of 90%. Several surfactant systems, with high and low surface modulus, were used to clarify the effect of the surfactant adsorption layer on the gas permeability across the foam films. In one series of experiments, glycerol was added to the foaming solutions to clarify how changes in the composition of the aqueous phase affect the rate of bubble coarsening. The experimental results are interpreted by a new theoretical model, which allowed us to determine the overall gas permeability of the foam films in the systems studied, and to decompose the film permeability into contributions coming from the surfactant adsorption layers and from the aqueous core of the films. For verification of the theoretical model, the gas permeability determined from the experiments with bulk foams are compared with values, determined in an independent set of measurements with the diminishing bubble method (single bubble attached at large air-water interface) and reasonably good agreement between the results obtained by the two methods is found. The analysis of the experimental data showed that the rate of bubble Ostwald ripening in the studied foams depends on (1) type of used surfactant-surfactants with high surface modulus lead to much slower rate of Ostwald ripening, which is explained by the reduced gas permeability of the adsorption layers in these systems; (2) presence of glycerol which reduces the gas solubility and diffusivity in the aqueous core of the foam film (without affecting the permeability of the adsorption layers), thus also leading to slower Ostwald ripening. Direct measurements showed that the foam films in the studied systems had very similar thicknesses, thus ruling out the possible explanation that the observed differences in the Ostwald ripening are due to different film thicknesses. Experiments with the Langmuir trough were used to demonstrate that the possible differences in the surface tensions of the shrinking and expanding bubbles in a given foam are too small to strongly affect the rate of Ostwald ripening in the specific systems studied here, despite the fact that some of the surfactant solutions have rather high surface modulus. The main reason for the latter observation is that the rate of surface deformation of the coarsening bubbles is extremely low, on the order of 10(-4) s(-1), so that the relaxation of the surface tension (though also slow for the high surface modulus systems) is still able to reduce the surface tension variations down to several mN/m. Thus, we conclude that the main reason for the reduced rate of bubble Ostwald ripening in the systems with high surface modulus is the low solubility and diffusivity of the gas molecules in the respective condensed adsorption layers (which have solid rather than fluid molecular packing).     

Dynamic surface tension analysis of dodecyl sulfate association complexes

First, a novel calibration method is used to expand the current understanding of spherical drop growth and elongation that occurs during on-line measurements of surface pressure using the dynamic surface tension detector (DSTD). Using a novel surface tension calibration method, the drop radius is calculated as a function of time from experimental drop pressure data and compared to the theoretical drop radius calculated from volumetric flow rate. From this comparison, the drop volume at which the drop shape starts to deviate ( approximately 4 mul) from a spherical shape is readily observed and deviates more significantly by approximately 6 mul drop volume (5% deviation in the ideal spherical drop radius) for the capillary sensing tip employed in the DSTD. From this assessment of drop shape, an experimental method for precise drop detachment referred to as pneumatic drop detachment is employed at a drop volume of 2 mul (two second drops at 60 mul/min) in order to provide rapid dynamic surface tension measurements via the novel on-line calibration methodology. Second, the DSTD is used to observe and study kinetic information for surface-active molecules and association complexes adsorbing to an air-liquid drop interface. Dynamic surface tension measurements are made for sodium dodecyl sulfate (SDS) in the absence and presence of either tetra butyl ammonium (TBA) or chromium (III). Sensitive, indirect detection of chromium and other multiply charged metals at low concentrations is also investigated. The DSTD is utilized in examining the dynamic nature of SDS: cation association at the air-liquid interface of a growing drop. Either TBA or Cr(III) were found to substantially enhance the surface tension lowering of dodecyl sulfate (DS), but the surface tension lowering is accompanied by a considerable kinetic dependence. Essentially, the surface tension lowering of these DS: cation complexes is found to be a fairly slow process in the context of the two second DSTD measurement. The limit of detection for both SDS and chromium (III) is in the 300-400 part-per-billion (by mass) range.