Adsorption of sodium dodecylsulfate on chrysotile

Adsorption of sodium dodecylsulfate (SDS) onto chrysotile from aqueous solutions was investigated along with varying temperature, ionic strength and surface treatments. Commercial chrysotile fibers were treated by sonication or extensive washings. The ratio of adsorbed SDS per gram of chrysotile is approximately constant with varying chrysotile masses. A steady state is reached after about 2 h of contact between SDS and chrysotile. In general, less surfactant is adsorbed on the sonicated chrysotile than on the extensively washed chrysotile. For the sonicated chrysotile, isotherms presented an adsorption maximum in the region of the surfactant critical micelle concentration, when the experiments were carried out without ionic strength control. The adsorption maximum is due to the presence of magnesium ions in the solution, which can form complexes with dodecylsulfate ions. For the extensively washed chrysotile, the isotherm behavior is similar to that obtained with sonicated chrysotile in the presence of an inert electrolyte. No significant difference in adsorption of SDS on the extensively washed chrysotile was observed when varying temperature or ionic strength. The adsorption of SDS was found to be dependent on the prior surface treatment.     

电解质水溶液在丙酸十二铵-四氯化碳溶液中的增溶

表面活性剂在非极性溶剂中形成的反胶束在催化反应、光化学、蛋白质苹取分离等方面有着广泛的应用问．这些应用与反胶束的性质有着密切的关系，而增溶水后的反胶束其形状和大小都会发生很大的变化．增溶不同水量的反胶束的微极性、酸碱性、微勤度等已有不少文献报导［2－5］．一些不溶于非极性溶剂而溶于水的物质可以溶解在非极性溶剂中的反胶束核心水团中，这个现象被称为二次增溶．其中，电解质的二次增溶对于研究配体转换反应。酶催化反应问及改变反胶束内部的微环境有着十分重要的作用，Aebi和Weibush回首先研究了有水存在时N。CI在A…     

Electrochemical origin of voltage-controlled molecular conductance switching

We have studied electron transport in bipyridyl-dinitro oligophenylene-ethynelene dithiol (BPDN) molecules both in an inert environment and in aqueous electrolyte under potential control, using scanning tunneling microscopy. Current-voltage (IV) data obtained in an inert environment were similar to previously reported results showing conductance switching near 1.6 V. Similar measurements taken in electrolyte under potential control showed a linear dependence of the bias for switching on the electrochemical potential. Extrapolation of the potentials to zero switching bias coincided with the potentials of redox processes on these molecules. Thus switching is caused by a change in the oxidation state of the molecules.     

聚电解质复合物溶解性研究

报道了聚电解质复合物的一种新的溶剂体系———离子表面活性剂剂的水溶液 ,研究了表面活性的用量及结构、温度、外加小分子电解质对复合物溶解性的影响 ,初步探讨了溶解机理 ,通过扫描电镜观察了复合物溶解后在溶液中的形态 .研究表明 ,当复合物与离子表面活性剂定量结合到一定程度时 ,就会使复合物发生溶解 .表面活性剂碳链长度的增加、温度的提高均会对复合物的溶解有不同程度的促进 .加入少量的无机电解质如氯化钠 ,会促进复合物的溶解 ,若氯化钠加入量过多 ,反而不利于复合物的溶解 .复合物的溶解机理被认为是表面活性剂的解离作用和疏水作用二者的协同 .     

Marangoni flow in micro-channels

A novel electrochemical method for driving fluids in micro-channels is presented. The principle is based upon the onset of Marangoni flow along the interface between an aqueous solution (mobile phase) and an organic electrolyte polymer gel coated on the inner walls of the micro-channel. The gradient of surface tension responsible for the fluid motion arises from local changes in the surface charge. The excess charge is determined by the ionisation of surfactant species at the gel coating|aqueous electrolyte interface which is effectively dependent on the Galvani potential difference. Potential differences of less than a volt between two closely spaced silver band electrodes along the micro-channel can generate zones of high and low surface tension, promoting the motion of the aqueous electrolyte.     

Der Einfluß von Elektrolyten auf die Stabilisierung dünner wäßriger Filme durch nichtionogene Tenside

The stability of thin aqueous films between different hydrophobic phases was investigated in dependence of the condition of hydratation of the polyoxyethylene surfactant. The hydratation was changed by addition of different, high concentrated electrolytes. On exceeding a critical electrolyte concentration the films become unstable, if they are limited by at least one phase, which is sufficiently polar. The critical concentrations depends on the kind of organic liquid and electrolyte respectively and the number of ether groups in the surfactant molecule. The observed effect of destabilization is explained by strengthening of interaction of far extending dehydrated surfactant molecules with the organic phase. Further possible mechanism of film destabilization are discussed.     

Role of the Surfactant Structure in the Behavior of Hydrophobic Ionic Liquids within Aqueous Micellar Solutions

The behavior of an ionic liquid (IL) within aqueous micellar solutions is governed by its unique property to act as both an electrolyte and a cosolvent. The influence of the surfactant structure on the properties of aqueous micellar solutions of zwitterionic SB‐12, nonionic Brij‐35 and TX‐100, and anionic sodium dodecyl sulfate (SDS) in the presence of the “hydrophobic” IL 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([bmim][PF₆]) is assessed along with the possibility of forming oil‐in‐water microemulsions in which the IL acts as the “oil” phase. The solubility of [bmim][PF₆] within aqueous micellar solutions increases with increasing surfactant concentration. In contrast to anionic SDS, the zwitterionic and nonionic surfactant solutions solubilize more [bmim][PF₆] at higher concentrations and the average aggregate size remains almost unchanged. The formation of IL‐in‐water microemulsions when the concentration of [bmim][PF₆] is above its aqueous solubility is suggested for nonionic Brij‐35 and TX‐100 aqueous surfactant solutions.     

Effect of salt on the equilibrium and nonequilibrium features of polyelectrolyte/surfactant association

The impact of an electrolyte on aqueous mixtures of oppositely charged macromolecules and surfactants is usually explained by assuming an equilibrium association between the components. In this work, it is shown that the nonequilibrium character of polyelectrolyte/surfactant systems plays a crucial role in the interpretation of the effect of salt. Experimental investigations of mixtures of sodium poly(styrenesulfonate) (PSS) and hexadecyltrimethylammonium bromide (CTAB) reveal two distinct effects of added sodium chloride (NaCl). At small and moderate NaCl concentrations, the major impact of the electrolyte is manifested in the reduction of the kinetically stable composition range in which the PSS/CTAB mixtures are trapped in the nonequilibrium colloidal dispersion state. The application of high salt concentrations, however, primarily affects the equilibrium phase properties through considerably decreasing the amount of surfactant bound to the polyelectrolyte.     

Electrolyte effect on adsorption and the phase transition from microstructures to nanostructures in ionic/ionic surfactants mixture

The effect of salt concentration on intermicellar interactions and aggregate structures of anionic and cationic-rich mixtures of CTAB (cetyltrimethylammonium bromide) and SDS (sodium dodecyl sulfate) were investigated with conductometry, surface tension, zeta potential, cyclic voltammetry measurements and by determining the surfactant NMR self-diffusion coefficients. The critical aggregate concentration (CAC), surface excess (Γ(max)), and mean molecular surface area (A(min)) were determined from plots of the surface tension (γ) as a function of the log of total surfactant concentration. The electrochemical behavior of cationic-anionic (catanionic) mixed surfactant and self-assembled surfactant monomers at Pt wire electrode were studied by cyclic voltammetry (CV). A variation in the peak current versus the total concentration of surfactant allow us to evaluate the CAC and related parameters from regular solution theory along with the diffusion coefficient of the electroactive species. It was observed that, for both the planar air/aqueous interface and micellar systems, the nonideality decreased as the amount of electrolyte in the aqueous medium was increased. Finally, we investigated the variations of electrostatic, transfer and steric free energy in phase transition between mixed micelle and vesicle in the presence of electrolyte using the presented model by our groups.     

Enantioseparations by capillary electrophoresis using chiral glycosidic surfactants. I. Evaluation of cyclohexyl-pentyl-beta-D-maltoside surfactant.

Chiral cyclohexyl-pentyl-beta-D-maltoside (CYMAL-5) surfactant was evaluated in the enantioseparation of charged racemic species by capillary electrophoresis. CYMAL-5 is a glycosidic surfactant (GS) with a chiral maltose polar head group and a cyclohexyl-pentyl hydrophobic tail. At concentrations above its critical micellar concentration (CMC), CYMAL-5 produces neutral micelles in aqueous media. The neutral micelles migrate at the velocity of the electroosmotic flow (EOF). As expected, the CYMAL-5 system was only useful for the enantioseparation of charged chiral solutes. The enantioresolution of the CYMAL-5 can be manipulated over a wide range of electrolyte composition, e.g., pH, ionic strength and surfactant concentration. In the presence of EOF, and in all cases, there is an optimum surfactant concentration for maximum enantioresolution, which is located at low surfactant concentration for strongly hydrophobic solutes and at high surfactant concentration for relatively hydrophilic solutes. The presence of an optimum surfactant concentration for maximum enantioresolution is attributed to the EOF. At low pH values where the EOF is negligible, enantioresolution increased with increasing surfactant concentration in the useful concentration range in a way similar to chromatography.     

用弱电解质理论研究水溶液中SDS胶团的电离行为

在临界胶团浓度以上,十二烷基硫酸钠(SDS)在溶液中形成聚集态的胶团,从而表现出不同于一般强电解质的电导行为.针对这一特点提出了一种胶团电离模型,即将胶团作为一种弱电解质,用弱电解质电导理论来描述其溶液电导的变化规律,导出SDS胶团电离度的计算式,并得到该溶液电导实测数据的验证.     

水溶性高分子链中磺酸盐基团含量的电导滴定测定法

研究了N ,N ,N 三甲基十六烷基溴化铵 (CTAB)与丙烯酰胺 (AM) 2 丙烯酰胺基 2 甲基丙磺酸钠盐(NaAMPS)二元共聚物P(AM co NaAMPS)的复合作用 .在复合作用过程中 ,由于不断释放出高导电性的无机盐小离子 ,故随着表面活性剂的加入 ,聚电解质水溶液的电导率不断增大 .当采用较低浓度 (0 0 0 1mol·L- 1 )且使二者的离子等摩尔量发生复合作用时 ,体系的电导率会发生明显的转折 .利用电导率的这一转折性变化 ,建立起了复合作用电导滴定法测定共聚物P(AM co NaAMPS)分子链中磺酸盐单体NaAMPS含量的新方法 .与元素分析进行比较的结果表明 ,上述复合作用电导滴定法可作为测定水溶性大分子链中磺酸盐单体含量的方便而又准确的方法 ,而且预计还可用作为测定水溶性大分子链中其它离子性基团含量的简捷方法     

THEORETICAL MODELING OF IONIC SURFACTANT ADSORPTION ON MINERAL OXIDE SURFACES

A model for the adsorption of ionic surfactants on oppositely charged solid surfaces of uniform charge density is developed. The model is based on the assumption that, on the solid surface, adsorbed surfactant monomers, monolayered and bilayered surfactant aggregates of different sizes and specifically adsorbing ions of added electrolyte constitute a mixture of hard discs. It means that only excluded area interactions between the surface discs are taken into account. To avoid a rapid two-dimensional condensation of the adsorbed surfactant the potential energy per molecule in the surface aggregates, which is a sum of chemical and electrostatic interactions, is assumed to decrease linearly with the increasing aggregate size. The electrostatic interactions of ionic species with the charged solid surface are described in terms of the Guy-Chapman theory of the double layer formation. The appropriate equations for adsorption isotherms of surfactant and electrolyte ions are derived and used to predict the experimental adsorption isotherms of DTAB on the precipitated silica at two different salt concentrations in the aqueous solution, On the basis of the obtained results the evolution of the adsorbed phase structure and the charge of silica particles with an increasing surface coverage is discussed.     

Association and phase behavior of hydrophobically modified photoresponsive poly(acrylamide)s in the presence of ionic surfactant

 The extent of association between the cationic surfactant TTAB and a series of hydrophobically modified polyacrylamides (HPAMs) containing an N-n-alkyl and substituted azobenzene hydrophobic sidegroup has been studied utilizing a cationic surfactant-selective membrane electrode. Binding of TTAB to the polymer hydrophobes is found to increase with increasing hydrophobicity of the hydrophobe. In the presence of electrolyte, aqueous solutions of HPAMs and ionic surfactant exhibit an associative phase separation. The temperature or clearing point (CP) at which the system goes from a one phase to two-phase system are reported. The area of the two-phase region is found to increase with increasing electrolyte concentration, hydrophobicity of the hydrophobe for the high molecular weight HPAMs, and decreasing hydrophobicity for low molecular weight HPAMs. Exposure of HPAMs containing an azobenzene hydrophobe to UV light results in a decrease in interaction between the hydrophobe and surfactant and a corresponding decrease in the CP due to conversion of azobenzene from the more hydrophobic trans form to the less hydrophobic cis isomer. Received: 23 September 1996 Accepted: 11 March 1997     

An extraction technique for analytical sample preparation in aqueous solution based on controlling dispersion of ionic surfactant assemblies in isotachophoretic migration

An extraction technique for analytical sample preparation in aqueous solution has been developed based on controlling dispersion of ionic surfactant assemblies. An extraction technique was realized based on controlling dispersion of the ionic surfactant assemblies in their isotachophoretic migration during the extraction by arranging the solutions of leading electrolyte, ionic surfactant and terminating electrolyte in order and applying voltage. Potential of the technique for analytical sample preparation in aqueous solution has been demonstrated by extracting a model sample of four alkylphenones, which were analyzed by HPLC after the extraction. The extraction showed concentration effects on all the four alkylphenones of butyrophenone, valerophenone, hexanophenone and heptanophenone in the model sample. The enrichment factors were 5.29, 7.70, 7.25 and 7.49 for the four alkylphenones of butyrophenone, valerophenone, hexanophenone and heptanophenone, respectively. Linear relationship was obtained with all the four alkylphenones between their chromatographic peak areas before and after the extraction in the range of concentration from 0.05 ppm to 1.5 ppm. The RSD of the chromatographic peak areas in triplicate extractions was 7.97%, 3.75%, 2.91% and 4.45% for butyrophenone, valerophenone, hexanophenone and heptanophenone, respectively. Advantages of the extraction technique developed include ease of operation, low reagent cost, no consumption of organic solvents and no requirement for additional phase separation.     

Interactions between cationic starch and anionic surfactants

The surface tensions and the phase equilibria of dilute aqueous cationic starch (CS)/surfactant systems were investigated. The degree of substitution of the CS varied from 0.014 to 0.772. The surfactants investigated were sodium dodecyl sulphate (SDS), potassium octanoate (KOct), potassium dodecanoate (KDod) and sodium oleate (NaOl). The concentrations of CS were 0.001, 0.01 and 0.1 w%.Critical association concentrations (cac) occur at surfactant concentrations well below the critical micelle concentrations of the surfactants, except for KOct, KDod and NaOl at the lowest CS concentrations investigated (0.001 w%). The surface tensions of CS/surfactant solutions decrease strongly already below the cac. This is attributed to the formation of surface active associates by ion condensation. Associative phase separation of gels formed by CS and surfactant takes place at extremely low concentrations when the surfactant/polymer charge ratio is somewhat larger than 1. The gel is higly viscous and contains 40–60% water, depending on the concentration of electrolyte, the surfactant hydrocarbon chain length and the nature of the polar head of the surfactant.The concentration at which the phase separation occurs decreases with increasing surfactant chain length and the concentration of simple electrolyte, factors that promote micelle formation. This indicates that the gels are formed by association of CS to surfactant micelles. When surfactant well in excess of charge equivalence is added, the gels dissolve because the CS/surfactant complexes acquire a high charge.     

Control over colloidal aggregation in monolayers of latex particles at the oil-water interface

The controlled generation of 2D aggregate networks is studied experimentally using micrometer-sized polystyrene latex particles attached to the oil-water interface. Starting from an initially crystalline monolayer, appropriate combinations of carefully added electrolyte and surfactant enable control over both the fractal dimension and the kinetics of aggregation. Remarkably, the colloidal crystals formed upon first spreading remain stable, even for days, when substantial amounts of electrolyte are added to the aqueous phase. Pressure-area isotherms reveal a slow time evolution of the electrostatic dipole-dipole interaction. When the electrostatic interaction has been sufficiently weakened, aggregation proceeds in well-defined, reproducible manner. The aggregation process is analyzed using quantitative video microscopy. The evolution of the cluster size distribution and its moments is characterized, and static and dynamic scaling exponents are derived to identify the nature of the aggregation process. In the range of concentrations studied here, the kinetics all agree with a "fast", diffusion-limited cluster type of aggregation. However, the fractal dimension strongly depends on the composition of the aqueous subphase. Rather dense structures are found when only electrolyte is used, whereas more open structures are obtained when even small amounts of surfactant are added. It is suggested that this structural dependency is related to the effect of surfactant on the contact angle and its consequences for the anisotropic nature of the capillary interactions.     

Separation of phenols from aqueous micellar solutions by cloud point extraction

The cloud point technique was used to recover phenol, 4-methylphenol, and 4-nitrophenol from aqueous solutions using oxyethylated methyl dodecanoates as nonionic surfactants. Oxyethylated methyl dodecanoates are convenient nonionic surfactants for such separations. Their cloud points can be easily modified by a change in surfactant hydrophilicity or by the addition of a second nonionic surfactant and/or an electrolyte. The use of the hydrophile lipophile balance is preferred to model the cloud point of oxyethylated methyl dodecanoates and their mixtures with other surfactants. The composition of the surfactant-rich phase depends on electrolyte type and the overheating. The phase can contain only 5-15% of water. Recovery of phenols changes in the order 4-nitrophenol >4-methylphenol > phenol and is increased in the presence of sodium chloride. The presence of salting-out electrolytes is preferred both to decrease the cloud point and to increase the efficiency of extraction.     

Ionic rectification properties of a bipolar interface consisting of a cationic surfactant and cation-exchange membrane

A novel bipolar interface that consists of cationic surfactant and cation-exchange membrane was successfully prepared in an aqueous electrolyte system. This bipolar interface shows a ionic rectification behavior similar to that observed in bipolar membranes. However, different from bipolar membranes, this system has a total rectification behavior, where we cannot observe the occurrence of a water-splitting phenomenon, which always occurs in the bipolar membrane process under reverse bias conditions.