Adsorption of ionic surfactants

Two adsorption models for ionic surfactants based on the Frumkin equation are examined to describe the measured surface tension isotherms of a series of alkali dodecylsulphates. In the model A the number of optimization parameters is reduced by additional modeling. The adsorption of counter-ions in the Stern layer is described via forming of ionic bonds, which free energy is significantly higher than that obtained by the model B. Concurrently the lateral interactions on the water/air interface are also found to be orders of magnitude stronger. Thus, the values of the adsorption parameters are more realistic, which supports the model A as a more relevant one.     

Surface tension and adsorption behavior of mixtures of diacyl glycerol arginine-based surfactants with DPPC and DMPC phospholipids

The binary surface interactions of some novel cationic diacyl glycerol arginine-based surfactants with model phospholipids, which are often used as model membrane components, are studied at 25 °C in aqueous solutions of 0.1 M sodium chloride. The surfactants are 1,2-dimyristoyl-rac-glycero-3-O-(N^α-acetyl-l-arginine) hydrochloride (1414RAc) and 1,2-dilauroyl-rac-glycero-3-O-(N^α-acetyl-l-arginine) hydrochloride (1212RAc), and they are important as potential antimicrobial agents which are biodegradable and with less toxicity than other cationic surfactants. The phospholipids are 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC). The equilibrium and dynamic surface tension of each surfactant, each phospholipid, and some of their binary mixtures are studied using the bubble surfactometry method at constant area or pulsating area conditions. In addition, the surface densities of pure and mixed monolayers of these compounds at the air/water interface are probed with infrared reflection–absorption spectroscopy (IRRAS). Steady state and dynamic surface tension synergism, or antisynergism in one case, and synergistic adsorption effects are detected for the mixed dispersions studied. The enhanced adsorption detected with IRRAS, and the enhanced dynamic and steady state surface tension lowering indicate strong miscibility and net attractive interactions between the compounds in the adsorbed mixed monolayers.     

Synthesis of a novel type of hybrid fluorocarbon ionic surfactants containing polyoxyethlene chain

A novel type of hybrid ionic surfactants containing oxyethylene chain and fluorocarbon chain in one molecule, n-C₈F₁₇SO₃⁻N⁺(C₂H₅)₃(CH₂CH₂O)_nH (n = 4.0, ∼4.1, 8.7, 13.2, 17.8, 22.3), were prepared. The compounds were achieved from the reaction of polyethylene glycol and perfluorooctanesulfonyl fluoride in the presence of Et₃N. The evaluation of their behavior at the air-water interface has been studied from measurements of surface tension versus variation of concentration, and the properties of the hybrid surfactants are not consistent with the empirical rule observed from the fluorinated nonionic surfactant.     

The effect of electrolyte on ionic surfactant adsorption

For submicellar solutions of ionic surfactants rigorous thermodynamic expressions are presented which show that the surfactant adsorption will not depend on electrolyte concentration c₃ at constant surfactant concentration c₁, if there is no corresponding dependence on c₁ at constant c₃. Results which indicate otherwise are inconsistent with thermodynamics.     

Interactions between polyampholytes and ionic surfactants

The interactions of two partially charged ampholytic terpolymers [consisting of acrylamide, sodium 2-acrylamido-2-methylpropanesulphonate, and 2-(methacryloyloxyethyl)trimethylammonium chloride segments with molar compositions 80/12/08 and 80/08/12] and two fully charged ampholytic copolymers (containing only the two latter comonomers with molar compositions of 80/20 and 50/50), with cationic surfactants [tetradecyl- trimethylammonium bromide (TTAB) and cetyltrimethylammonium bromide (CTAB)] and the anionic surfactant sodium dodecylsulphate (SDS), are investigated. The studies include phase behaviour (swelling, solubilisation, precipitation), viscometry, electrical conductivity, and potentiometry (bromide ion and surfactant ion-specific electrodes). The 80/08/12 and 80/12/08 polyampholytes swell in water and are solubilised in the presence of cationic or anionic surfactants above a particular surfactant concentration that is proportional to the polymer concentration. The polyampolyte 80/20 is soluble in water but precipitates in the presence of TTAB, whereas 50/50 is insoluble in water and in the presence of TTAB, but is solubilised upon addition of SDS. The results indicate that TTAB binds to 80/12/08 with little or no cooperativity. Solubilisation appears to be the result of the increasing polyelectrolyte character of the polyampholyte upon neutralisation of its charged sites by bound surfactant ions of opposite charge. The binding of TTAB by the 50/50 polyampholyte is very weak and non-cooperative. In contrast, 80/20 binds TTAB cooperatively, much like a true polyelectrolyte-surfactant system of opposing charges. In particular, the binding is characterised by the existence of a critical aggregation concentration. A partial phase diagram for this system has been determined from the TTA⁺-electrode potential data. The behaviour of true polyelectrolytes and polyampholytes, with respect to their interaction with surfactants, is discussed. Received: 22 July 1998 Accepted: 14 September 1998     

Theoretical model for moisture adsorption on ionic liquids: A modified Brunauer-Emmet-Teller isotherm approach

The adsorption of atmospheric water on the air-liquid interface of ionic liquids is analyzed by means of a modified version of the Brunauer-Emmet-Teller (BET) multilayer adsorption isotherm including lateral interactions between adsorbed molecules, treated in a mean-field fashion. Recently reported experimental results of water adsorption on hydrophobic ionic liquids of the 1-alkyl-3-methyl imidazolium tetrafluoroborate (C_nMIM-BF₄) family are analyzed in the present theoretical framework. The calculated values of the lateral interaction are seen to be compatible with the Keesom dipole-dipole interaction in water, confirming the validity of the multilayer assumption hypothesis. A somehow surprisingly ordered hydrophilic-like adsorption of atmospheric water is suggested to take place in the free surface of hydrophobic ILs of the imidazolium family.     

Adsorption of cationic multicharged surfactants at liquid–gas interface

We present the review of the existing methods for describing adsorption at fluid interfaces that may be applicable for multiple charge cationic surfactant structures of various architectures—multiheaded (e.g., dicephalic) structures and multimeric surfactants (e.g., dimeric (so-called gemini), trimeric, tetrameric, etc.). We discuss the role of the prefactor the in the Gibbs adsorption equation originating from the number of charges present in the adsorbed layer and the reasons for the deviation from its thermodynamic value. We present several models of adsorption that can be used to describe surface tension isotherms and appreciate the role of prof. Peter Kralchevski in their development. Application of molecular dynamics methods combined with the approach based on the thermodynamic models of multicharged surfactant adsorption may lead to an explanation of some experimentally observed phenomena and can provide the basis for the development of novel materials designated for a variety of applications.     

Synthesis and properties of triethylalkylammonium perfluorooctanesulfonates (APFOS)

Six ionic surfactants containing a perfluorooctanesulfonic anion and a positively charged ammonium in a molecule, R_FSO₃⁻N⁺Et₃C_nH_2n+1 (n=2, 4, 6, 8, 10 and 12), were prepared from perfluorooctanesulfonyl fluoride, triethylamine and linear alkanol. Solution properties of triethylalkylammonium perfluorooctanesulfonates (APFOS) have been measured in terms of surface tension. The values of critical micelle concentration (cmc) decrease with an increase of N-alkyl chain length, and the logarithm of the cmc decreases linearly with increasing N-alkyl chain length (n≥6), while the negative values of standard free energy for the adsorption become larger as the N-alkyl chain length increases.     

Aqueous immiscibility of cholinium chloride ionic liquid and Triton surfactants

The immiscibility windows of aqueous solutions containing the ionic liquid cholinium chloride (N_1112OHCl) and the non-ionic surfactants Triton X-100 and Triton X-102 have been determined by the cloud point method at temperatures ranging from T = (298.15 to 333.15) K. The experimental values have been correlated by using two well-known equations. The tie-lines have been ascertained by means of density and refractive indices measurement, and the experimental data have been modeled by the Othmer–Tobias, Bancroft and Setschenow equations. The use of cholinium chloride involves greater demixing capacity than other imidazolium-based ionic liquids.     

A simple isotherm equation for describing gas adsorption on heterogeneous microporous solids

A simple isotherm equation for describing gas adsorption on solids showing heterogeneity of microporous structure is proposed. It is shown that this equation gives a good representation of the experimental data of argon, nitrogen and benzene adsorption on different types of activated carbons. Its parameters may be used to characterize heterogeneity of microporous structure of the solids.

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Eine einfache Isotherme zur Beschreibung der Gas-Adsorption an heterogenen mikroporösen Feststoffen

Zusammenfassung Es wird eine einfache Isotherme zur Beschreibung der Gasadsorption an Feststoffen mit heterogener mikroporöser Struktur vorgeschlagen. Es wird gezeigt, daß diese Gleichung die experimentellen Daten für die Adsorption von Argon, Stickstoff und Benzol an verschiedenen Typen von Aktivkohle gut beschreibt. Die Parameter der Isotherme können zur Charakterisierung der Heterogenität der mikroporösen Struktur von Festkörpern herangezogen werden.

     

Synthesis and characterization on a novel series of protic pyrrolidinium surfactants

<正>A novel series of protic tertiary pyrrolidinium surfactants were prepared and characterized by different techniques.These compounds show good conductivity and efficient ability to reduce surface tension.Thermogravimetric analysis proves their high thermal stability at decomposition temperatures over 250℃.Their lyotropic and thermotropic liquid crystalline properties are also discussed.     

A simple and generalized model for predicting the density of ionic liquids

A simple and accurate model to predict the density of ionic liquids is presented. The proposed model is based on a generalized correlation that has been conveniently modified and experimental literature data have been used to fit the five model parameters, to finally propose an equation that allows predicting densities of any ionic liquid. The model uses the critical temperature, the critical volume, the normal boiling temperature and the molecular mass to estimate the density at temperatures commonly used in ionic liquid applications (270–360 K). A set of 602 density data for 146 ionic liquids has been used in the study. The results were compared with predictions of ten generalized corresponding states principle correlations available in the literature. These generalized correlations have not been applied to ionic liquids before so the appropriateness and accuracy of these models to ionic liquid density estimation are unknown until now. Results show that the new simple correlation gives low deviations and can be used with confidence in thermodynamic and engineering calculations.     

On the theory of adsorption kinetics of ionic surfactants at fluid interfaces

The kinetic equation to describe the adsorption process of ionic surfactants (derived in part 1) will be solved numerically. The results show the effect of parameters such as ion valencyz, thickness of theDL x ^–1, and surfactant parameters_eq,K, andK _ads on the adsorption process. The results can be used to decide whether the model can explain experimental data on charged surfactant molecules or not.Nomenclature c concentration - c_e bulk concentration in equilibrium - C =c/c _e dimensionless concentration - D diffusion coefficient - e proton charge - F Faraday's constant - f ₀ =e/kTdimensionless potential - k Bolzmann's constant - K _ads rate constant of adsorption - K _des rate constant of desorption - K(f ₀) coefficient of electrostatic deceleration - K = _eq /c _e Henry's constant - R gas law constant - t time - T absolute temperature - z electrovalence - ₀ adsorption of ions - _eq equilibrium value of _o - = ₀/ _eq dimensionless adsorption - , constants - dielectric constants - x Debye-Hückel reciprocal distance - =Dt/K ² dimensionless time - electric potential     

Synthesis and surface activities of organic solvent-soluble fluorinated surfactants

A variety of fluorinated surfactants soluble in organic solvent were prepared, including C₈F₁₇SO₂NHC_nH_2n+1 (n = 2, 4, 6, 8, 10), C₈F₁₇SO₂NHR (R = C₆H₁₁, C₆H₅), C₈F₁₇SO₂N(C_nH_2n+1)₂ (n = 1, 2, 3, 4) and C₈F₁₇SO₂NH(CH₂)_nNHO₂SC₈F₁₇ (n = 6, 10). Their surface activities in various organic solvents were determined by surface tension measurement. The results showed that these fluorinated surfactants can reduce the surface tension of both polar and non-polar organic solvents. In general, organic solvents with strong polarity or long alkyl chain are beneficial to increase the surface activity of these polar fluorinated surfactants. By comparing fluorinated surfactants with the same fluorocarbon segment and connecting group, C₈F₁₇SO₂N(C_nH_2n+1)₂ (n = 1, 2, 3, 4) showed lower surface activity in organic solvents than C₈F₁₇SO₂NHC_nH_2n+1 (n = 2, 4, 6, 8) with an equal carbon number of the solvophilic group. Through surface tension vs. concentration curves given for N-octyl perfluorooctanesulfonamide in various organic solvents, a break point like the critical micelle concentration of ordinary surfactants in aqueous solutions was observed, and the effect of the different types of organic solvents on adsorption and aggregation behavior was also studied.     

Novel and accurate mathematical simulation of various models for accurate prediction of surface tension parameters through ionic liquids

Ionic Liquids (ILs) as a novel class of liquid solvent simultaneously carry the positive characteristics of both molten salts and organic liquids. Remarkable positive properties of ILs have such as low vapor pressure and excellent permittivity have encouraged the motivation of researchers to use them in various applications over the last decade. Surface tension is an important physicochemical property of ILs, which its experimental-based measurement has been done by various researchers. Despite great precision, some major shortcomings such as high cost and health-related problems caused the researchers to develop mathematical models based on artificial intelligence (AI) approach to predict surface tension theoretically. In this research, the surface tension of two novel ILs (bis [(trifluoromethyl) sulfonyl] imide and 1,3-nonylimidazolium bis [(trifluoromethyl) sulfonyl] imide) were predicted using three predictive models. The available dataset contains 45 input features, which is relatively high in dimension. We decided to use AdaBoost with different base models, including Gaussian Process Regression (GPR), support vector regression (SVR), and decision tree (DT). Also, for feature selection and hyper-parameter tuning, a genetic algorithm (GA) search is used. The final R²-score for boosted DT, boosted GPR, and boosted SVR is 0.849, 0.981, and 0.944, respectively. Also, with the MAPE metric, boosted GPR has an error rate of 1.73E-02, boosted SVR has an error rate of 2.35E-02, and it is 3.36E-02 for boosted DT. So, the ADABOOST-GPR model was considered as the primary model for the research.     

Surface tension of 1-alkyl-3-methylimidazolium based ionic liquids with trifluoromethanesulfonate and tetrafluoroborate anion

The amount of available accurate experimental data on the surface tension of ionic liquids is still limited; in many cases the data are rare or even absent. In the present study, air-liquid interfacial tension data were determined experimentally for five 1-C_n-3-methylimidazolium based ionic liquids (n = 2, 4, and 6), three with trifluoromethanesulfonate and two with tetrafluoroborate anion, at atmospheric pressure in the temperature range from 268 to 356 K. The resultant surface tension data are average values of the measurements repeated many times at each set point temperature. The accuracy of the results, was confirmed by employing the Wilhelmy plate and the du Noüy ring methods in parallel, using the Krüss K100MK2 tensiometer. For the Wilhelmy plate data the combined standard uncertainty is estimated to be about 0.05 mN m⁻¹. The data obtained by du Noüy method show about up to seven times greater scatter than those obtained by the Wilhelmy plate method. To the 50 up to now published surface tension values for the five studied ionic liquids the present study adds further 175 data points. In contrast to that of n-alkanes, the surface tension of 1-alkyl-3-methylimidazolium based ionic liquids decreases and their surface entropy increases with the cation alkyl chain length.     

Electrical conductivity study of the self-association of ionic surfactants in solution in ethyleneglycol,formic acid and formamide

The self-association of several cationic surfactants has been investigated by means of solubility and electrical conductivity measurements in ethyleneglycol, formic acid and formamide. Operational critical micelle concentrations (CMC_op) have been obtained from the vs. surfactant concentrationC plots by the usual interpolation procedure. It has been found that for the surfactant-solvent systems investigated the value of CMC_op increases with the extent of theC-range investigated. This result together with others concerning the effect of temperature and surfactant chain length reveal that the CMC_op-values have an ambiguous meaning concerning the surfactant self-association. Comparison of the vs.C plots for cetyltrimethylammonium chloride and tetramethylammonium chloride, for instance, reveals that some surfactant self-association takes place, probably leading to small, highly ionized surfactant aggregates, but the systems do not show true critical micelle concentration. Solubility measurements as a function of temperature lead to the same conclusion. The results are discussed according to our present understanding of the process of micellization and the necessity of using solvents of very high cohesive energy density in order to observe, with ionic surfactants, true CMCs corresponding to a highly cooperative association process. This appears to be the case only with water and hydrazine, not with formamide and other less cohesive solvents.     

离子型共价有机框架材料的制备及对染料吸附性能的研究

茜素红(Alizarin Red,AR)作为蒽醌类染料中的重要组成,由于其具有优异的特性,在染料和酸碱指示剂等方面被广泛使用。但是AR具有毒性高、结构复杂以及化学需氧量(COD)值大等原因,使其成为了主要污染物之一,去除水体中的茜素红染料污染物已经成为了目前亟待解决的问题。共价有机框架材料作为一种新型的多孔有机材料,由于其具有比表面积大,孔径均一和可设计的独特优势,已经广泛应用吸附和分离等方面。因此,以三醛基间苯三酚和溴化乙锭为构筑单元,通过水热的方法合成一种二维离子型共价有机框架材料(TpEB-COF)。对制备的TpEB-COF进行相关表征,包括X射线衍射仪(XRD),扫描电镜(SEM)和能量色散谱仪(EDS)等。然后将制备的TpEB-COF作为固体吸附剂,将其应用对水中AR的吸附,研究了不同吸附时间和不同pH值对吸附过程的影响。实验结果证明制备的离子型共价有机框架材料具有良好的晶型结构。同时,对实验数据分析表明,离子型共价有机框架材料对于茜素红的吸附符合准二级动力学方程和Langmuir吸附模型,吸附效率为82.8%,最大吸附量为828 mg g-1。本研究不仅为共价有机框架材料的设计和合成奠定坚实的基础,而且拓展了离子型共价有机框架材料的应用范围,促进共价有机框架材料的发展。     

Micellar parameters of diblock copolymers and their interactions with ionic surfactants

The interactions of non-ionic amphiphilic diblock copolymer poly（oxyethylene/oxybutylene）(E₃₉B₁₈) with anionic surfactant sodium dodecyl sulphate（SDS） and cationic surfactant hexadecyltrimethylammonium bromide（CTAB） were studied by using various techniques such as surface tension,conductivity,steady-state fluorescence and dynamic light scattering.Surface tension measurements were used to determine the critical micelle concentration（CMC） and thereby the free energy of micellization(△G_mic),free energy of adsorption(△G_ads),surface excess concentration（Γ） and minimum area per molecule（A）.Conductivity measurements were used to determine the critical micelle concentration（CMC）,critical aggregation concentration（CAC）,polymer saturation point（PSP）,degree of ionization（α） and counter ion binding（β）. Dynamic light scattering experiments were performed to check the changes in physiochemical properties of the block copolymer micelles taken place due to the interactions of diblock copolymers with ionic surfactants.The ratio of the first and third vibronic peaks（I₁/I₃） indicated the polarity of the pyrene micro environment and was used for the detection of micelle as well as polymer-surfactant interactions.Aggregation number（N）,number of binding sites（n） and free energy of binding （△G_b） for pure surfactants as well as for polymer-surfactant mixed micellar systems were determined by the fluorescence quenching method.     

Synthesis and properties of cationic surfactants with tuned hydrophylicity

A series of pyridinium-based cationic surfactants has been synthesised and their amphiphilic properties have been studied by conductivity and surface tension measurements. The modification of the substitution pattern on the pyridinium ring by hydrophobic moieties (methyl vs. hydrogen and presence or not of condensed benzene ring) gave the opportunity to investigate structure–activity relationships. Characterization by conductivity and surface tension measurements shed light on the behaviour at the air/water interface and in the micellar environment. In particular, the tendency to form ion pairs at very low concentration was evidenced for all the surfactants substituted on the ring, but not for the simple pyridinium ones. The formation of ion pairs affects both the conductivity and the surface tension plots, showing that a series of steps is involved during the adsorption to the air/water surface. An attempt was made to qualify the single steps in the adsorption at the surface layer. Those steps were attributed to different chemical species (free surfactant ions or ion pairs) and to different arrangements of the surfactant. This work also represents a contribution of investigation at very low surfactant concentrations and high surface tension values.