Adsorption of Cationic Surfactants on Highly Dispersed Silica

Comparative study was made of adsorption of cationic surfactants, decamethoxine, ethonium, and cetyltrimethylammonium bromide, on a highly dispersed amorphous silica at different pH values. Contrary to the adsorption of monoquaternary ammonium compound, cetyltrimethylammonium bromide, the adsorption of bis(quaternary ammonium) compounds, ethonium and decamethoxine, was found to be caused mainly by electrostatic interaction. The adsorption of antiseptic decamethoxine is reversible at pH 6; this may be used to design carriers capable of controlled drug release into the surrounding medium.     

Stability and Adsorption Properties of Suspensions of Finely Dispersed Silica in the Presence of Cationic Surfactants

Interrelation between the coagulation rate, adsorption and electrokinetic properties of silica polydisperse suspensions in the presence of cationic surfactants is studied. The highest coagulation rate is observed in a certain concentration range of the cationic surfactants. When pH values increases, an increasing amount of cationic surfactant is required to achieve maximal coagulation rate. For bisquaternary cationic surfactants, ethonium and decamethoxine, maximal coagulation rate is observed at concentrations by an order of magnitude lower than for monoquaternary cetyltrimethylammonium bromide. It is concluded that the suspensions lost their stability as a result of both neutralization of particle surface charge and flocculating effect of the cationic surfactants. Moreover, the flocculation mechanism depends on the cationic surfactant nature and physicochemical parameters of the medium, ionic strength and pH.     

Adsorption of a cationic surfactant, miramistin, from aqueous solutions on the surface of highly dispersed silica

The adsorption of a universal antiseptic agent, the cationic surfactant miramistin, on the surface of highly dispersed silica has been studied. It has been shown that, when miramistin is adsorbed from acidic premicellar solutions, the main contribution to miramistin binding with the surface is made by hydrogen bonding between amide groups of surfactant molecules and silanol groups of silica, which is, at higher pH values, accompanied by ionic interaction between positively charged quaternary nitrogen atoms of miramistin and negatively charged dissociated silanol groups. In the case of adsorption from a micellar solution, an increase in the surface concentration of miramistin is almost independent of solution pH, because the second layer is predominantly formed due to hydrophobic interactions.     

Adsorption of cationic and nonionic surfactants on a SiO<Subscript>2</Subscript> surface from aqueous solutions: 2. Adsorption of dodecylpyridinium bromide and Triton X-100 from mixed solutions

Adsorption of cationic (dodecylpyridinium bromide) and nonionic (Triton X-100) surfactants from their mixed aqueous solutions on a SiO₂ surface at pH 3.6, 6.5, and 10 is studied by the UV spectroscopy, capillary zone electrophoresis, and wetting measurements. It is shown that the adsorption of cationic and nonionic surfactants from mixed solutions is accompanied by synergistic effects manifesting themselves as an enhanced adsorption of both surfactants compared to their adsorption from individual solutions. The effect of second component becomes most pronounced under conditions when differences in adsorption abilities of individual surfactants are rather large (at pH 3.6 and 10). It is shown that the adsorption of surfactants from mixed solutions can be controlled by the adsorption ability of components via the variations in solution pH.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 2, 2005, pp. 281–287.Original Russian Text Copyright © 2005 by Kharitonova, Ivanova, Summ.     

Keto-Enol tautomerization of quercetin in solutions of a cationic surfactant,miramistin

Tautomeric transformations of quercetin in solutions of a cationic surfactant, miramistin, have been spectrophotometrically studied. It has been established that, at pH ≥ 6, monoanions of enol-form quercetin are irreversibly transformed into keto-form monoanions, with the rate of this process depending on surfactant concentration and solution pH. It has been shown that the enol tautomer of quercetin is more stable in aqueous solutions, while the ketone form is stabilized in miramistin-containing media. The apparent dissociation constants have been determined for the enol (pK _a ^a= 6.60) and ketone = 5.64) tautomeric forms of quercetin in micellar solutions of miramistin.     

Mixed Adsorption Layers of Nonionic and Cationic Surfactants on Quartz

Surfactant adsorption on quartz and wetting of glass by aqueous solutions of tetradecyltrimethylammonium bromide, Triton X-100, and their mixtures are studied. It is shown that synergistic adsorption of surfactants from mixed solutions occurs in the region of low concentrations. In the region of high concentrations, mixed molecular aggregates of the cationic and nonionic surfactants are formed on the surface. The structure of the mixed adsorption layers is discussed.     

Dependence of the solubility of natural flavonoids in water on the concentration of miramistin,polyvinylpyrrolidone, and human serum albumin

In organized media of the cationic surfactant miramistin and the polymers polyvinylpyrrolidone and human serum albumin, the solubility of natural flavonoids quercetin and rutin increased by one or two orders of magnitude. The increase was more significant for hydrophobic quercetin than for hydrophilic rutin. The solubility also depended on the structure and self-organization of molecules in organized media and the site of flavonoids in them. The calculated binding constants increased in the series polyvinylpyrrolidone < miramistin < human serum albumin.     

Adsorption of cationic and nonionic surfactants on a SiO<Subscript>2</Subscript> surface from aqueous solutions: 1. Adsorption of dodecylpyridinium bromide and Triton X-100 from individual solutions

Adsorption of cationic surfactant dodecylpyridinium bromide and nonionic surfactant Triton X-100 from aqueous solutions on the surface of SiO₂ particles is studied at various pH values (3.6, 6.5, and 10). The data on the adsorption are compared with the data on the wetting of quartz plates by solutions of these surfactants. Adsorption of both studied surfactants on the SiO₂ surface is greatly dependent on solution pH. The mechanism of adsorption of the cationic surfactant is shown to be changed when passing to the alkaline pH region. Triton X-100 does not demonstrate a substantial change in the adsorption mechanism in the pH range from 3.6 to 10.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 2, 2005, pp. 274–280.Original Russian Text Copyright © 2005 by Kharitonova, Ivanova, Summ.     

Adsorption and Micellization in Solutions of Dodecylpyridinium Bromide–Nonionic Surfactant Mixtures

Dependences of the surface tension of aqueous solutions of cationic (dodecylpyridinium bromide) and nonionic (Tween 80, Triton X-100) surfactants and their mixtures on total surfactant concentration and solution composition were studied. The values of critical micellization concentration (CMC) and excess free energy of adsorption were determined from tensiometric measurements. Based on Rubingh–Rosen model (approximation of the theory of regular solutions), the compositions of micelles and adsorption layers at the solution–air interface as well as parameters of interaction between the molecules of cationic and nonionic surfactants were calculated for the systems indicated above. It was established that, in the case of surfactant mixtures with considerable difference in the CMCs, the micelles of individual surfactant with lower CMC value are formed. The effect of negative deviation from the ideality during the adsorption of surfactants from mixed solutions at the solution–air interface was disclosed. It was shown that the interaction energy depends significantly on the composition of mixed systems.     

Surface and bulk properties of aqueous binary mixtures of Pluronic F68 and low-molecular-weight cationic surfactants: 2. Wetting and modifying effects of mixed solutions

Wetting and adsorption modification of polystyrene surface with aqueous solutions of F68-cationic surfactant mixtures are studied. The synergism of wetting is revealed. It is established that the degree of synergism upon wetting is determined by the synergism of surfactant adsorption on a solid surface and peculiarities of the formation of mixed adsorption layers of surfactants. It is shown that low-molecular-weight cationic surfactants can be used to increase the efficiency of the modification of polymer surfaces with Pluronics.     

酰胺基团对Gemini表面活性剂表面活性和聚集行为的影响

本文合成了含酰胺基团和不含酰胺基团的两类Gemini阳离子表面活性剂,测定了其表面活性参数,研究了酰胺基团对表面活性剂的表面活性和聚集行为的影响。结果表明,酰胺基团提高了Gemini阳离子表面活性剂的临界胶团浓度,降低了胶团聚集数,增强了胶团微极性,增大了表面活性剂的饱和吸附量。     

Behavior of surface-active substances in aqueous solution and on solid surfaces

The interactions of cationic (CSA), anionic (ASA), and nonionic surfactants (NSA) with each other in aqueous solution and on solid surfaces are studied. To establish the mechanism of the adsorption of ASA and NSA from aqueous solutions onto layered silicates, modified with CSA, data on the interaction of corresponding surfactants in aqueous solutions of binary mixtures were used. It was shown that interactions between CSA and ASA led to the formation of cationic surfactants both in solution and on the surfaces of modified aluminosilicates. It was concluded that by analogy with solutions of binary mixtures of NSA on modified silicate surfaces, interaction occurs only with physically adsorbed CSA. With cations of modifier, chemically bonded to the active centers of the silicates, NSA reacts via a hydrophobic mechanism. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 3, pp. 180–184, May–June, 2009.     

季铵盐型Gemini表面活性剂在金表面的吸附行为

以邻苯二酚(CC)为电化学探针, 利用循环伏安、交流阻抗等方法研究了不同阳离子Gemini表面活性剂(C16H33(CH3)2N-C4H8-N(CH3)2C16H33 (C16-C4-C16)、C12H25(CH3)2N-C4H8-N(CH3)2C12H25 (C12-C4-C12)、C8H17(CH3)2N-C4H8-N(CH3)2C8H17 (C8-C4-C8))在金电极表面的吸附性能. 结果表明, CC在KNO3溶液中可产生两对峰; 当向溶液中加入阳离子Gemini表面活性剂时, 第一对峰降低, 第二对峰升高, 峰电位差变大; 碳链长的表面活性剂对CC的氧化还原峰的影响较大. 同样, 碳链长的表面活性剂使电极界面的阻抗增大较多, 使石英晶片的频率变化较大. 根据CC的第一个氧化峰的面积随表面活性剂吸附的变化, 估测了它们的吸附模式. 发现这三种表面活性剂在金电极表面的吸附基本符合Langmuir吸附模型.     

Synergistic effect of water layer and divalent metal ions in a model oil sand on bitumen liberation from solids surface

In this work, we offer a direct evidence to illustrate the synergistic effect of water layer and divalent metal ions in oil sands on bitumen liberation from solids surface. A model oil sand was constructed by coating bitumen on the glass surface with a water layer containing divalent metal ions inserted between them. The bitumen liberation behaviors were investigated by placing the model oil sands in various pH solutions. It was found that the water layer facilitated the bitumen liberation, while the presence of Ca²⁺ or Mg²⁺ in the water layer played a different role on the bitumen liberation depending on the solution pH. It was believed that the variation of the bitumen liberation was attributed to the changes of surface wettability arising from the adsorption of natural surfactants on the solids and bitumen surfaces. The preferential adsorption of Ca²⁺ or Mg²⁺ on the solids and bitumen surfaces acted as either a barrier to disturb the cationic surfactants adsorbing or a bridge to anchor the anionic surfactants. The findings in this work are important for understanding the bitumen liberation behaviors and give a guideline of how controlling the water chemistry when processing the oil sands by water-based bitumen extraction processes.     

Reverse Flow of Mixed Surfactant Solutions after Their Capillary Rise

The reverse flow (i.e., the efflux from glass capillaries occurring after the stop of capillary rise) of mixed aqueous solutions of nonionic (Triton X-100) and cationic (cetyl- and dodecyltrimethylammonium bromides) surfactants is studied. The effect of electrolytes (salts and acids) on the process kinetics and the wetting in these systems is investigated. Possible causes of the reverse flow are discussed. They are related to the peculiar features of the interaction of nonionic and cationic surfactants with glass and to the differences in the surfactant adsorption from quiescent and moving solutions. It is shown that the wetting by the mixed surfactant solutions, including its kinetics, can be controlled by the addition of electrolytes.     

The effect of surfactants on the pH transition interval of bromothymol blue immobilized on XAD 4

Cationic, anionic and non-ionic surfactants adsorb readily from aqueous solution on to Amberlite XAD 4. The ionic surfactants cause the pH of the solution in contact with the resin to differ from that in the bulk of solution, cationic surfactants increasing the interfacial pH and anionic surfactants decreasing it. This causes a shift in the pH transition interval of a co-adsorbed pH indicator when measured with respect to the bulk solution. The quantity of ionic surfactant adsorbed tends to a constant value (presumably monolayer coverage) with increasing solution concentration, this amount being a function of the individual surfactant, whereas non-ionic surfactants readily form multilayers. Significant adsorption occurs when the surfactant possesses at least 14 carbon atoms.     

Synergism in the spreading of hydrocarbon-chain surfactants on polyethylene film-anionic and cationic mixtures by a two-step procedure

A study has been made of the adsorption, interaction, and spreading of mixtures of anionic and cationic surfactants at the aqueous solution/polyethylene (PE) interface. When a drop of an aqueous solution of an anionic or cationic hydrocarbon-chain surfactant is placed on a highly hydrophobic PE film (contact angle of water > 90 degrees ), it spreads to an area very little larger than that of a drop of water of the same volume. If the anionic and cationic hydrocarbon-chain surfactant solutions are mixed prior to being applied to PE film, synergism is small, if any, and the reproducibility of the experimental results is poor. However, when the cationic and anionic aqueous solutions are applied on the PE film in a sequential manner, a remarkable synergism in spreading is observed and the results are very reproducible. The area spread by an aqueous solution of the anionic-cationic mixture may be more than 400 times that of aqueous solutions of the same volume and surfactant concentration of the individual surfactant components. Previous work in this laboratory on surfactant systems showing synergism in spreading on PE film, but only weak interaction at the aqueous solution/air interface, showed that the synergy was due to changes at the aqueous solution/PE interface and not to the changes at the aqueous solution/air or PE/air interface. Investigation of the adsorption behavior at the aqueous solution/solid interface of two of the anionic-cationic mixtures studied here indicates the reason for differences in spreading behavior observed with different anionic-cationic mixtures. The more similar the adsorption tendencies at the solid/aqueous solution interface of the anionic and cationic surfactants, and the closer their adsorption to an equimolar monolayer there, the stronger their interaction there and the greater their enhancement of the spreading. A mechanism is proposed for the synergy in spreading observed, based upon the difference between the surface tension in the precursor film at the spreading interface and that at the top of the spreading drop.     

阴、阳离子表面活性剂混合体系在硅胶/水及硅胶/矿化水界面上的吸附

研究阴、阳离子表面活性剂混合体系(十二烷基氯代吡啶,辛基磺酸钠,辛基三乙基溴化铵/十二烷基苯磺酸钠)在硅胶,纯水和硅胶,矿化水界面上的吸附作用,探讨阴(阳)离子表面活性剂的存在对阳(阴)离子表面活性剂吸附作用的影响．结果表明,阴离子表面活性剂的存在基本不影响阳离子表面活性剂在带负电固体表面的吸附;而阳离子表面活性剂的存在却使本来吸附量就不大的阴离子表面活性剂在带负电的固体表面上不再吸附．在矿化水中阳离子表面活性剂的吸附量比在纯水中明显降低．从硅胶表面吸附机制解释了所得结果．     

Adsorption of Cationic Surfactants on Silica Surface: 1. Adsorption Isotherms and Surface Charge

Adsorption isotherms of cationic surfactant, dodecylpyridinium chloride, on an Aerosil OX50 and isotherms of surface charge against the background of 0.001- and 0.1-M KCl solutions at pH 7 and 9 were measured and analyzed. Different forms of adsorption isotherms of surfactants at low and high electrolyte concentrations are explained from differences in the formation of the surface charge of Aerosil. Comparison of the isotherms of surfactant adsorption and surface charge allowed us to make conclusions about the surfactant orientation and structure of an adsorption layer, as well as to determine the fraction of surfactant molecules in the first and second adsorption layers.     

Use of surfactants to remove water-based inks from plastic film: effect of calcium ion concentration and length of surfactant hydrophobe

Effective plastic film deinking could permit the reuse of recycled polymer to produce clear film, reduce solid waste for landfills, reduce raw material demand for polymer production, and aid process economics. In this study, the deinking of a commercial polyethylene film printed with water-based ink was studied using surfactants in the presence of hardness ions (calcium ions) at various pH levels. The electrostatic properties of ink particles in a washing bath were also investigated. Synthetic anionic surfactant or fatty acid soap in the presence of calcium ions at alkaline pH levels was found to be nearly as effective at deinking as cationic, nonionic, or amphoteric surfactants alone. However, adding calcium ions decreases the deinking effectiveness of cationic, nonionic, and amphoteric surfactants. Increasing the length of the ionic surfactant hydrophobe enhances deinking. Zeta potential measurements showed that water-based ink particles in water reach the point of zero charge (PZC) at a pH of about 3.6, above which ink particles are negatively charged, so cationic surfactant tends to adsorb better on the ink than anionic surfactant above the PZC in the absence of calcium. As the cationic surfactant concentration is varied between 0.005 and 25 mM, the zeta potential of the ink particles reverses from negative to positive owing to adsorption of cationic surfactant. For anionic surfactants, added calcium probably forms a bridge between the negatively charged ink and the negatively charged surfactant head groups, which synergizes adsorption of the surfactant and aids deinking. In contrast, calcium competes for adsorption sites with cationic and nonionic surfactants, which inhibits deinking. All the surfactants studied here disperse ink particles effectively in the washing bath above pH 3 except for the ethoxylated amine surfactant.