Competitive adsorption in the system: carboxymethylcellulose/surfactant/electrolyte/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The adsorption of carboxymethylcellulose (CMC) in the presence or absence of the surfactants: anionic SDS, nonionic Triton X-100 and their mixture SDS/TX-100 from the electrolyte solutions (NaCl, CaCl₂) on the alumina surface (Al₂O₃) was studied. In each measured system the increase of CMC adsorption in the presence of surfactants was observed. This increase was the smallest in the presence of SDS, a bit larger in the presence of Triton X-100 and the largest when the mixture of SDS/Triton X-100 was used. These results are a consequence of formation of complexes between the CMC and the surfactant particles. Moreover, the dependence between the amount of surfactants’ adsorption and the CMC initial concentration was measured. It comes out that the surfactants’ adsorption amount is not dependent on the CMC initial concentration and moreover, it is unchanged in the whole measured concentration range. The influence of kind of electrolyte, its ionic strength as well as pH of a solution on the amount of the CMC adsorption at alumina surface was also measured. The amount of CMC adsorption is larger in the presence of NaCl than in the presence of CaCl₂ as the background electrolyte. It is a result of the complexation reaction between Ca²⁺ ions and the functional groups of CMC belonging to the same macromolecule. As far as the electrolyte ionic strength is concerned the increase of CMC adsorption amount accompanying the increase of electrolyte ionic strength is observed. The reason for that is the ability of electrolyte cations to screen every electrostatic repulsion in the adsorption system. Another observation is that the increase of pH caused the decrease of CMC adsorption. The explanation of this phenomenon is connected with the influence of pH on both dissociation degree of polyelectrolyte and kind and concentration of surface active groups of the adsorbent.     

钽掺杂六方相氧化钨对Sr2+的吸附:Zeta电位的测量及吸附机理的研究

研究Ta掺杂六方相氧化钨(hex-WO₃)材料在吸附Sr²⁺过程中其表面zeta电位的变化情况,并进一步探讨了吸附过程的热力学及吸附机理。结果表明：(1)在实验pH值范围内,Ta掺杂hex-WO₃悬浮液的zeta电位值随溶液中电解质的价态增大而增大;(2)且zeta电位随体系中离子强度的增加而增大;(3) Ta掺杂hex-WO₃对Sr²⁺的吸附容量随着温度降低而增大,随着离子强度的增加而减少;(4)吸附过程的吸附焓为－47 kJ·mol^-1,且Sr²⁺离子与材料表面之间主要为化学相互作用;(5) Ta掺杂hex-WO₃对Sr²⁺吸附过程主要为材料表面吸附及材料孔道内离子交换共同作用。     

Micellar solutions of ionic surfactants and their mixtures with nonionic surfactants: Theoretical modeling vs. Experiment

Here, we review two recent theoretical models in the field of ionic surfactant micelles and discuss the comparison of their predictions with experimental data. The first approach is based on the analysis of the stepwise thinning (stratification) of liquid films formed from micellar solutions. From the experimental step-wise dependence of the film thickness on time, it is possible to determine the micelle aggregation number and charge. The second approach is based on a complete system of equations (a generalized phase separation model), which describes the chemical and mechanical equilibrium of ionic micelles, including the effects of electrostatic and non-electrostatic interactions, and counterion binding. The parameters of this model can be determined by fitting a given set of experimental data, for example, the dependence of the critical micellization concentration on the salt concentration. The model is generalized to mixed solutions of ionic and nonionic surfactants. It quantitatively describes the dependencies of the critical micellization concentration on the composition of the surfactant mixture and on the electrolyte concentration, and predicts the concentrations of the monomers that are in equilibrium with the micelles, as well as the solution’s electrolytic conductivity; the micelle composition, aggregation number, ionization degree and surface electric potential. These predictions are in very good agreement with experimental data, including data from stratifying films. The model can find applications for the analysis and quantitative interpretation of the properties of various micellar solutions of ionic surfactants and mixed solutions of ionic and nonionic surfactants.     

Influence of ionic strength and pH on the first 60 min of Pseudomonas aeruginosa attachment to ZnSe and to TiO2 monitored by ATR-IR spectroscopy

Establishing the factors which influence the attachment of bacteria to surfaces is important in both preventing and enhancing biofilm formation. The initial hour of attachment of Pseudomonas aeruginosa to ZnSe and to TiO₂ from solutions of different ionic strength and pH was studied using in situ attenuated total reflection infrared (ATR-IR) spectroscopy. The TiO₂ surface was prepared by dip-coating a ZnSe internal reflection element, which produced a 50 nm thick, continuous flat film. At pH 6.3 attachment was found to increase with ionic strength up to 0.03 mol l⁻¹ but to decrease at 0.15 mol l⁻¹. At an ionic strength of 0.003 mol l⁻¹ attachment increased with pH from 4 to 6.3 to 10, but at ionic strength of 0.03 mol l⁻¹ attachment was greater at pH 6.3 than at pH 10. The influence of ionic strength appears to be due to charge factors and/or related changes in the degree of extension of bacterial surface polymers. The complex trends in the influence of pH on attachment can not be explained solely in terms of bacterial and substrate charge, bacterial surface polymer extension or bacterial metabolic activity.     

Influence of inorganic electrolytes on the retention of polyethyleneglycol by a nanofiltration ceramic membrane

Retention properties of a nanofiltration ceramic membrane were investigated with single polyethyleneglycol (PEG) solutions and mixed PEG/inorganic electrolyte solutions. The rejection coefficient of PEGs was found to decrease in the presence of ions. It was shown that the effect of ions on the retention of neutral solutes increases with the electrolyte concentration. This phenomenon was ascribed to the partial dehydration of PEG molecules induced by the surrounding ions. This argument was confirmed by using various electrolytes (KCl, LiCl and MgCl₂). It was found that the lowering of the PEG rejection coefficients follows the Hofmeister series, i.e. Mg²⁺ > Li⁺ > K⁺. Experimental data were used to compute the resulting decrease in the Stokes radius of PEG molecules in the presence of the various electrolytes.     

Electrokinetic characterization of polystyrene–non-ionic surfactant complexes

An experimental study on the electrophoretic mobility (μ_e) of polystyrene particles after the adsorption of non-ionic surfactants with different chain lengths is described. Two sulphate latexes with relatively low surface charge densities (3.2 and 4.8 μC cm⁻²) were used as solid substrate for the adsorption of four non-ionic surfactants, Triton X-100, Triton X-165, Triton X-305 and Triton X-405, each one with 9–10, 16, 30 and 40 molecules of ethylene oxide (EO), respectively. The electrophoretic mobility of the polystyrene–non-ionic surfactant complexes was studied versus the amount of adsorbed surfactant (Γ). The presence of non-ionic surfactant onto particles surface seems to produce a slight shifting of the slipping plane because the mobilities of the different complexes display a very small decreasing. The increase in the number of EO chains in the surfactant molecule seems to operate as a steric impediment which decreases the number of adsorbed large surfactant molecules. The electrophoretic mobilities of the latex–surfactant complexes with maximum adsorption were measured versus the pH and ionic strength of the dispersion. While the different complexes showed a similar qualitative behaviour compared with that of the bare latex against the pH, the adsorption of the surfactant reduces the typical maximum in the μ_e−log[electrolyte].     

Preconcentration and decomposition of perfluorinated carboxylic acids on an activated charcoal cartridge with sodium biphenyl reagent and its determination at microg L(-1) level on the basis of flow injection-fluorimetric detection of fluoride ion

Perfluorinated surfactants of heptafluorobutylate and pentadecafluorooctanoate ions were adsorbed on an activated charcoal cartridge and decomposed with sodium biphenyl (SBP) reagent to form inorganic fluoride ion. The fluoride ion thus formed was determined by flow injection analysis (FIA) using quercetin-Zr complex as a fluorimetric reagent, where λ_ex and λ_em were 422 and 491 nm, respectively. The limit of detection for fluoride ion by the FIA system was developed to 1.1 × 10⁻⁶ M (signal to noise ratio of three), when 50% (v/v) tetrahydrofuran (THF) was used as a dissolving solvent for quercetin. The perfluorinated surfactants in the sample solution were quantitatively adsorbed on the cartridge containing 100 mg of activated charcoal and were decomposed with 0.5 mL of sodium biphenyl reagent after drying thoroughly by flowing through dry nitrogen gas. The fluoride ion formed was recovered with 3 mL of purified water as an eluent, and it was determined by the fluorimetric flow injection system. The blank fluorescence signal accompanied during the adsorption/decomposition on the cartridge was reduced by washing the activated charcoal with acetone. The blank signal was also observed from dimethoxyethane, which was used in sodium biphenyl reagent. When 600 mL sample solution was used and 200 times enrichment was applied, the heptafluorobutylate and pentadecafluorooctanoate ions at the concentrations of 2.1 μg L⁻¹ were quantitatively recovered as fluoride ion, and the limit of detections for the perfluorinated surfactants were 0.3 and 0.3 μg L⁻¹ for the two perfluorinated surfactants, respectively (3 sigma of the blank signal).     

New forms of McKay-Perring equations for mixed electrolyte solutions

Pan, H. and Han, S., 1993. New forms of McKay-Perring equations for mixed electrolyte solutions. Fluid Phase Equilibria, 90: 289-306.

A rigorous derivation is given for new forms of the McKay-Perring equations and the partial differential equation relating the activity coefficients of two electrolytes in mixed electrolyte solutions. They all have simple and symmetrical forms when the independent variables are the total ionic concentration and the fraction of ionic concentration. However, the simple and symmetrical forms remain only when the electrolytes are of the same charge types and when the independent variables are ionic strength and the fraction of ionic strength. The method of surface fitting is introduced to evaluate the McKay-Perring equations. The calculated results for four systems are in good agreement with those from the Pitzer equations.     

Micelle–monomer equilibria in solutions of ionic surfactants and in ionic–nonionic mixtures: A generalized phase separation model

On the basis of a detailed physicochemical model, a complete system of equations is formulated that describes the equilibrium between micelles and monomers in solutions of ionic surfactants and their mixtures with nonionic surfactants. The equations of the system express mass balances, chemical and mechanical equilibria. Each nonionic surfactant is characterized by a single thermodynamic parameter — its micellization constant. Each ionic surfactant is characterized by three parameters, including the Stern constant that quantifies the counterion binding. In the case of mixed micelles, each pair of surfactants is characterized with an interaction parameter, β, in terms of the regular solution theory. The comparison of the model with experimental data for surfactant binary mixtures shows that β is constant — independent of the micelle composition and electrolyte concentration. The solution of the system of equations gives the concentrations of all monomeric species, the micelle composition, ionization degree, surface potential and mean area per head group. Upon additional assumptions for the micelle shape, the mean aggregation number can be also estimated. The model gives quantitative theoretical interpretation of the dependence of the critical micellization concentration (CMC) of ionic surfactants on the ionic strength; of the CMC of mixed surfactant solutions, and of the electrolytic conductivity of micellar solutions. It turns out, that in the absence of added salt the conductivity is completely dominated by the contribution of the small ions: monomers and counterions. The theoretical predictions are in good agreement with experimental data.     

Interaction of ions with phosphatidylcholine and phosphatidylethanolamine at the n-heptane/water interface : II. Hydrophobic ions

Electrocapillary phenomena at the n-heptane/water interface in the presence of phosphatidylcholine or phosphatidylethanolamine in alkane were studied by the drop-volume technique. The regulating role of the electric field was established in phospholipid interaction with inorganic ions: changes in interfacial pressure at the n-heptane/water interface with addition of electrolytes were observed only when an electric field was applied to the system of two immiscible liquids. It is suggested that ions can penetrate and bond by phospholipid functional groups at the phase boundary only after reorientation of the latter in the electric field. As in the case of ionic surfactants, change in interfacial pressure was directly proportional to the cube root of the concentration of electrolyte. It is assumed that as a result of preferential binding by phospholipid functional groups of ions of one sign, lipid molecules are charged and at the phase boundary behave themselves like ionic surfactants. Experiments with salts of multicharged ions, La³⁺, [Fe(CN)₆]³⁻, and [Fe(CN)₆]⁴⁻, have shown that mainly phospholipid functional groups bind cations.     

Contribution of migration current to the voltammetric deposition and stripping of lead with and without added supporting electrolyte at a mercury-free carbon fibre microdisc electrode

In order to assess the contribution and analytical significance of migration, electrochemical studies on the deposition and stripping of lead at a carbon fibre microelectrode (diameter of 10 μm) have been undertaken in aqueous solutions containing 1 mM lead ions with variable KNO₃ supporting electrolyte concentrations (10⁻¹ to 10⁻⁵ M), as well as in the total absence of deliberately added supporting electrolyte. The methodology involved the application of cyclic voltammetry to characterise the Pb²⁺ (solution)+2e⁻Pb (metal) process in both the reduction (Pb deposition) and stripping (Pb dissolution) directions. The use of a mercury-free carbon surfaces means that the lead stripping does not occur from the amalgam state, as is commonly the case in anodic stripping voltammetry. In the deposition step, the current rises sharply with potential in response to a lead nucleation-growth process and then reaches an almost potential independent limiting value. The stripping step, obtained on the reverse scan, exhibited oxidation peak currents resulting from the redissolution or stripping of the metal from the electrode surface. The influence of the electrolyte concentration and hence migration current at −0.8 V versus Ag/AgCl for the deposition process, as well on the redissolution peak current and the dependence of the voltammograms on scan rate (10–1000 mV) are discussed. Interestingly, neither deposition limiting nor stripping peak currents vary in a simple manner with added supporting electrolyte concentrations, with maximum values being observed at 10⁻⁵ M rather than zero concentration of added KNO₃. An important implication for the voltammetric determination of lead in low ionic strength media by the very sensitive technique of anodic stripping voltammetry is that use of the method of standard additions commonly employed to minimise unknown matrix problems, is prone to error when contributions to the process from migration current are important.     

Effect of MgO nanoparticles on ionic conductivity and electrochemical properties of nanocomposite polymer electrolyte

This paper analyzes the comparison between the performances and morphologies of the PMMA gel and composite electrolyte membrane with nanosized MgO particles. These polymer electrolytes were studied in detailed using XRD, DSC, SEM and AC impedance analysis. The conductivity enhancement has been attributed to the addition of ceramic filler that yields a significant increase of surface to volume ratio related to the decrease in glass transition temperature values in the composite polymer electrolyte. Good interfacial stability at the electrode/electrolyte interface resulted on account of the improved ion dissociation by ceramic filler and a rise in the room temperature conductivity (8.14 × 10⁻³ S cm⁻¹) due to the iono-covalent or Lewis acid–base bonds to the ions and ether oxygen base groups was also observed. Further enhancement of conductivity has been observed on MgO surface, as Lewis-acidic sites interact with both PMMA and ClO₄⁻ ions. The percentage of swelling was found to increase with increasing soaking periods upto 12 h. Beyond that soaking period, it was found that there was a negligible increase in the % of swelling.     

Thermochemic properties of NaCl and KCl solutions in mixtures of water with N,N-dimethylacetamide at 25°

Enthalpies of solution of NaCl and KCl in water- N, N-dimethylacetamide (DMA) mixtures (containing 0–20 mol.% of DMA) were measured at 25 ° C. The standard dissolution enthalpies for both investigated salts increase with increase in DMA content in the mixed solvent, in contrast with the dissolution enthalpies for other inorganic salts in the same mixtures examined so far. The calculated single-ion transfer enthalpies from water to water-DMA mixtures exhibit the opposite course with a distinct minimum for anions and a maximum for cations. The extrema of the ionic transfer enthalpies observed in all water-organic mixtures investigated thus far seem to be a consequence of the shape of the solvation enthalpy curves for Ph₄P⁺ and BPh₄⁻ ions which are the basis for the calculation of individual ionic contributions and which are hydrophobically hydrated in water-organic solvents.     

The Hofmeister series effect in adsorption of cationic surfactants--theoretical description and experimental results

Interfacial properties of cationic surfactants show strong dependence on the type of surfactant counterion or on the type of anion of a salt added to the surfactant solution. In the paper, the models of ionic surfactant adsorption that can take into account ionic specific effects are reviewed. Model of ionic surfactant adsorption based on the assumption that the surfactant ions and counterions undergo nonequivalent adsorption within the Stern layer was selected to describe experimental surface tension isotherms of aqueous solutions of a number of cationic surfactants. The experimental isotherms for: n-alkyl trimethylammonium cationic surfactants, namely: C(16)TABr (CTABr or CTAB), C(16)TACl, C(16)TAHSO(4), C(10)TABr and C(12)TABr as well as decyl- and dodecylpyridinium salts with and without various electrolyte anions as Cl(-), Br(-), F(-), I(-), NO(3)(-), ClO(4)(-) and CH(3)COO(-) were described in terms of the model and a good agreement between the theory and experiment was obtained for a wide range of surfactants and added electrolyte concentrations. A very pronounced Hofmeister effect in dependence of surface tension of cationic surfactants on the type of anion was found. Analysing this dependence in terms of the proposed model of ionic surfactant adsorption, strong correlation between "anion surface activity" (the model parameter accounting for ion penetration into the Stern layer), and the ion polarizability was obtained. That suggests that the mechanism related to the dispersive interaction of polarized ion with electric field at interface is responsible for Hofmeister series effects in surface activity of cationic surfactants. The same mechanism was proposed recently to explain the dependence of surface tension increase with electrolyte concentration on anion and cation type.     

Effect of small molecule surfactants on molecular parameters and thermodynamic properties of legumin in a bulk and at the air–water interface depending on a protein structure in an aqueous medium

This paper presents the effect of fatty acid salts, namely, Na-caprate and Na-palmitate on the legumin (11S globulin of Vicia Faba broad beans) molecular and thermodynamic properties in the bulk aqueous medium and at the air–water interface under different molecular states of the protein. That are the native state of the protein globule (pH 7.2, ionic strength of 0.05 mol dm⁻³), as well as the acidic denatured (pH 3.0, ionic strength of 0.01 mol dm⁻³) and the heat denatured ones (after heating at 90°C for 30 min, pH 7.2, ionic strength of 0.05 mol dm⁻³). In turn, an importance of the state of the small molecule surfactants in a solution in reference to the critical concentrations of micelle formation (CMC), for their effect on the protein properties, was also under our studying. The peculiarities of the legumin structure in the aqueous medium appeared in the different nature of the interactions between the protein and the fatty acid salts, as was indicated by the mixing calorimetry data. So, the hydrophobic contacts provided a basis for interactions between both the native and heat denatured legumin with the fatty acid salts. At the same time, the electrostatic interactions between the oppositely charged functional groups of the fatty acid salts and the acidic denatured protein formed principally a basis of their interactions in an aqueous medium. In response to interactions of the fatty acid salts with legumin the essential changes in the protein conformational stability, depending on both the protein molecular state and concentration of the fatty acid salts, were found using differential scanning calorimetry (DSC). The rather high level of the protein association was observed by light scattering in the bulk aqueous medium in the presence of the fatty acid salts. As this takes place, the surface hydrophilicity of the protein increased under the formation of the associates. The combined data of mixing calorimetry, differential scanning calorimetry and light scattering suggested the complex formation between legumin and the fatty acid salts. The interactions of the fatty acid salts with the protein produced a change in the surface activity for the mixture of the protein with the fatty acid salts. That is a decrease in the protein surface tension at the air–water interface for the mixed solutions in comparison with ones for both the protein and small molecule surfactant alone in the case of Na-caprate, and those are the intermediate values of the surface tension in the case of Na-palmitate. These results were observed independently of the protein state (native or acidic/heat denatured) in an aqueous medium. As this took place, the most dramatic increase in the surface activity was found for the mixtures of the acidic denatured protein with Na-caprate as if the most hydrophobic species were formed in this case. The combined data of mixing calorimetry, DSC, light scattering and tensiometry showed that the effect of the fatty acid salts on the legumin thermodynamic properties in a bulk and at interfaces is governed by a number of the key factors such as: a structure of both the protein and fatty acid salt (a length of the hydrocarbon chain); a degree of the protein association in the bulk aqueous phase (as a result of the interactions with the small molecule surfactants); a change in the protein conformational stability (flexibility) under the influence of the small molecule surfactants; as well as by the nature (hydrophobic, electrostatic) of the protein–small molecule surfactant interactions, determining ultimately the hydrophilic–lipophilic balance of the protein surface.     

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.     

Influence of operating conditions on the retention of phosphate in water by nanofiltration

The objective of this study was to investigate the retention of phosphate anions, H₂PO₄⁻ and HPO₄²⁻, by nanofiltration. The first part of this study deals with the characterisation of the NF200 membrane used in permeation experiments with aqueous solutions of neutral organic and charged inorganic solutes. In the second part the effects of feed pressure, ionic strength, concentration and pH on the retention of phosphate anions were investigated. Results show that the membrane is negatively charged, its pore radius is around 0.5 nm and the retention order for the salts tested was R(Na₂SO₄) > R(NaCl) > R(CaCl₂). The retentions of phosphate anions are in the order of 85% for H₂PO₄⁻ and 96% for HPO₄²⁻. They are relatively high when compared to retentions of other anions with the same charge. The retentions of phosphate anions, particularly the monovalent species, depend on the chemical parameters (feed concentration, ionic strength, and pH) and applied pressure. The experimental data were analysed using the Speigler–Kedem model and the transport parameters, i.e., the reflection coefficient (σ) and solute permeability (P_s) have been determined.