Investigation of the electrokinetic properties of paraffin suspension. 1. In inorganic electrolyte solutions

Although electrical properties of nonionogenic hydrophobic surface (solid or liquid) in water and/or electrolyte solutions have been studied for many decades, they are still not well recognized, especially as for the nature of the charge and potential origin. Similarly, water structure at such a surface is still extensively studied. One such system is paraffin wax/water (electrolyte). The zeta potentials and the particle diameters of this system were investigated in this paper. To obtain the suspension of paraffin in water or electrolyte solution (NaCl or LaCl3), the mixture was heated to ca. 70 degrees C and then stirred during cooling. For thus obtained suspensions, the zeta potential was determined as a function of time at 20 degrees C. Also the pH effect on the zeta potentials was investigated. The zeta potentials were calculated from Henry's equation. The results obtained by us are in agreement with those obtained earlier by others. They confirm that although H+/OH- are not surface charge creating ions, OH- ions to some extent are zeta potential determining for the paraffin surface. By use of the potentials and diameters, the electric charge for a spherical particle in the shear plane was calculated. These values are small in the range of 10(-3) C/m2. On the basis of the findings of water structure near hydrophobic surface and the calculated charges, it is concluded that in fact the potential may be created by immobilized and oriented water dipoles.     

Surface properties of mixed anionic/cationic surfactant solutions

Summary Published experimental surface pressures for mixtures of anionic and cationic surfactants are compared to what can be predicted from the surface behaviour of the separate constituents. Simple theory correctly predicts, for soluble surfactants, a large increase of surface pressure upon mixing an anionic and a cationic solution having the same surface pressure, and, for insoluble surfactants, a decrease of surface pressure upon mixing at a given area per long chain ion. These effects are due to the different adsorption characteristics of the four electroneutral combinations involved, and will occur even in the absence of specific surface interactions.

---

Zusammenfassung Es wurden bekannte Oberflächendrucke für Mischfilme von Aniontensiden und Kationtensiden mit theoretischen Voraussagen, begründet auf dem Grenzflächenverhalten der einzelnen Komponenten, verglichen. Die einfache Theorie sagt richtig voraus, daß die Mischung zweier wäßriger Lösungen von Aniontensid bzw. Kationtensid mit gleichem Oberflächendruck, eine starke Erhöhung des Oberflächendruckes zur Folge haben muß, während die Mischung zweier unlöslicher Filme bei gegebener Tensidadsorption den Oberflächendruck herabsetzt. Dieses Verhalten wird aufgrund der verschiedenen Adsorptionseigenschaften der vier betreffenden Salze gedeutet, und ist von spezifischen Oberflächenwechselwirkungen unabhängig.

     

Interaction of cationic surfactant and anionic polyelectrolytes in mixed aqueous solutions

Surfactant–polymer interactions in aqueous solutions have been studied using dynamic surface tension, polyelectrolyte titration, nephelometric turbidity, and dynamic light scattering. For the preparation of complexes, a technical cationic surfactant was used in combination with two poly(maleic acid-co-polymers) of similar structure but different hydrophobicity. The dynamic surface tensions of mixed solutions as functions of surfactant concentration at constant polyelectrolyte content, as well as changes in the surface activity due to the influence of polyanion at constant surfactant concentration are discussed in terms of a complex or aggregate formation in the bulk phase. The interaction of the surfactant with poly(maleic acid-alt-propene) (P-MS-P) and poly(maleic acid-alt--methylstyrene) (P-MS-MeSty), respectively, is strong in both cases and results in the formation of nanoparticles with properties depending on the composition of the corresponding mixture.     

Rheological properties of concentrated aqueous solutions of anionic and cationic polyelectrolyte mixtures

The rheological properties of aqueous solutions of poly(acrylic acid), poly(diallyldimethyldiammonium chloride), and their mixtures at 25°C have been studied. The concentrated solutions of the mixtures contain 18 wt % of both polymers taken at different ratios. The ratio of cationogenic and anionogenic groups φ varied from 0 to 0.4 is taken as a criterion for selection of mixture composition. An increase in φ, reflecting a more intense formation of polyelectrolyte complexes in solution, is accompanied by a significant rise in the low-frequency loss modulus and, especially, in the storage modulus, as well as by an increase in viscosity over the entire studied range of shear rates. This behavior may be explained by the presence of an additional spatial structure with junctions formed by interacting complementary charged groups. In the general case, the formation of poly(acrylic acid)-poly(diallyldimethyldiammonium chloride) polyelectrolyte complexes is said to take place in solution. The excess of rheological characteristics of mixture solutions over the corresponding characteristics of poly(acrylic acid) solutions is found to be the power function of parameter φ. The additional spatial network derived from polyelectrolyte complexes and occurring in solution is destroyed at lower shear stresses than is the network of intermolecular entanglements. At high shear stresses, orientational effects may cause phase separation of the systems owing to a change in the hydrophilic-hydrophobic balance between complexes of poly(acrylic acid) with poly(diallyldimethyldiammonium chloride) and water.     

Synergism in mixtures of cationic surfactant and anionic copolymers

Surface tension measurements have been made in aqueous solutions of anionic hemiesters of an alternating copolymer of maleic acid and styrene, MAS-n with n=0-12, in the presence of dodecyltrimethylammonium bromide, DTAB. A synergistic aspect of surface tension reduction efficiency was observed for all systems studied. The pseudo-phase separation approach and regular solution approximation have been applied, and the interaction parameter, beta, and the mole fraction of DTAB in the adsorbed layer (on a surfactant/repetitive unit basis), X, were obtained. Negative values of beta, ranging from -3 to -11, were calculated. On the other hand, the molar fraction of DTAB varies from 0.52 to 0.26. These results are discussed in terms of hydrophobic effects on the distribution of the aggregates between the interface and the bulk of the solution. The conditions predicted by the model to obtain synergism in the tension reduction efficiency are completely satisfied in all cases.     

Interaction of water-soluble cationic porphyrin with anionic surfactant

The interaction of a cationic water-soluble porphyrin, 5,10,15,20-tetrakis [4-(3-pyridiniumpropoxy)phenyl]porphyrin tetrakisbromide (TPPOC3Py), with anionic surfactant, sodium dodecyl sulfate (SDS), in aqueous solution has been studied by means of UV-vis, (1)H NMR, fluorescence, circular dichroism (CD) spectra and dynamic laser light scattering (DLLS), and it reveals that TPPOC3Py forms porphyrin-surfactant complexes (aggregates), including ordered structures J- and H-aggregates, induced by association with surfactant monomers below the SDS critical micelle concentration (cmc), and forms micellized monomer upon the cmc, respectively. The position of TPPOC3Py in the micelle is determined, which is not in the micelle core instead of intercalated among the SDS chains, most likely with the pyridinium group extending into the polar headgroup region of the micelle.     

Interfacial and micellar properties of some anionic/cationic binary surfactant systems. 1. Surface properties and prediction of surface tension

The surface tension equations of binary surfactant mixtures are established by combining the Szyszkowski equation for pure surfactant solutions and extended nonideal theory for mixed adsorption. They are then successfully applied to two relatively long-chain anionic/cationic binary surfactant systems: triethanolammonium dodecylpoly(oxyethylene)sulfate, as an anionic species (containing about 2 ethylene oxide units), mixed with dodecyltrimethylammonium bromide or hexadecyltrimethylammonium bromide. The composition of the mixed monolayer is mixing-ratio dependent and is slightly asymmetric: for overall equimolar mixtures, the larger mole fraction in the mixed monolayer is that of the more surface-active ion. The strong synergetic effects observed in the surface tension reduction efficiency are reflected by large negative β^s parameters, according to regular solution theory. They can be interpreted by the more negative adsorption free energy of each surfactant and the smaller area occupied by surfactant hydrocarbon chains in the mixed monolayer. Received: 20 April 1998 /Accepted in revised form: 27 August 1999     

Interactions of temperature-responsive anionic polyelectrolytes with a cationic surfactant

The interactions of temperature-responsive copolymers of sodium 2-acrylamido-2-methyl-1-propanesulfonate (AMPS) and N-isopropylacrylamide (NIPAM) with a cationic surfactant, dodecyltrimethylammonium chloride (DTAC), have been studied. The content of AMPS in the copolymers ranged from 1.1 to 9.6 mol%. The surface activity was higher for the polymers with lower AMPS content. It was found that DTAC undergoes association with the polymer chain, forming mixed polymer-surfactant micelles. The values of cac for the polymers were found in fluorescence studies using pyrene as the fluorescent probe. They were in the range 0.9-3.6x10(-3) M and were lower for polymers with higher AMPS content. An increase in DTAC concentration up to about its cmc results in a decrease of the LCST (lower critical solution temperature) of the copolymers, while further increase above the cmc results in an increase of the LCST. The minimum value of LCST in the presence of the surfactant is lower than the LCST of NIPAM homopolymer.     

A dually effective inorganic salt at inducing obvious viscoelastic behavior of both cationic and anionic surfactant solutions

Hydrazine nitrate (HN), an inorganic salt, was first found to have dual effects on inducing obvious viscoelasticity of both cationic and anionic surfactant solutions. It was interesting that the surfactant solutions exhibited characteristic wormlike micelle features with strong viscoelastic properties upon the addition of this inorganic salt. The rheological properties of the surfactant solutions have been measured and discussed. The apparent viscosity of the solutions showed a volcano change with an increase of the HN concentration. Correspondingly, the microstructures of the micelles in the solutions changed with the apparent viscosity. First, wormlike micelles began to form and grew with an increase of the HN concentration. Subsequently, the systems exhibited linear viscoelasticity with characteristics of a Maxwell fluid in the intermediate mass fraction range, which originated from a 3D entangled network of wormlike micelles. Finally, a transition from linear micelles to branched ones probably took place at higher HN contents. In addition, the origin of the dual effects brought by HN addition on inducing viscoelasticity in both cationic and anionic surfactant solutions was investigated.     

Phase behavior of mixed solution of a glycerin-modified cationic surfactant and an anionic surfactant

The phase behavior of mixed solution of newly synthesized monoglycerylcetyldimethylammonium chloride (MGCA) and sodium octyl sulfate (SOS) in water was investigated by cryo-transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), differential scanning calorimetry (DSC), and fluorescence polarizing for evaluation of the microviscosity of bilayers. No precipitate was observed in the mixed solution except at concentrations below 20 mM over all mixing ratios, and stable vesicles were formed in a considerably wide range of mixing ratio, even at the equimolar ratio. Vesicles formed in aqueous 1/1 MGCA/SOS mixture were found to exhibit no phase transition, and fluorescence polarizing measurements showed that the vesicle bilayers have a high fluidity. This flexibility allows the bilayers to have a spontaneous curvature, and thus vesicles rather than flat lamellae can be stabilized in the mixture even at the equimolar ratio. In addition, because the glycerin group of MGCA interacts strongly with water, the hydration repulsion contributes to prevent the bilayers consisting of MGCA and SOS from adhering and flocculating even though the charge neutralization between MGCA and SOS occurs at the equimolar ratio.     

混合表面活性剂双水相性质的研究

本文利用电导法及冷冻蚀刻实验技术研究了正负离子表面活性双水相上相中的液晶结构状态及其相关性质。在双水相相体积比一组成关系曲线上及上相电导率—组成曲线上,均存在明显的转折。转折处组成是有偏光现象的双水相与无偏光现象的双水相的分水岭,立方液晶导电能力与容纳水的能力强于层状液晶或六方液晶。冷冻蚀刻实验证实了无偏光现象的立方液晶的存在。本文对一些机理进行了讨论。     

Aqueous two-phase system of an anionic gemini surfactant and a cationic conventional surfactant mixture

The aqueous two-phase system formed by the mixture of dodecyltrimethylammonium bromide (DTAB) with a gemini surfactant O,O′-bis(sodium 2-lauricate)-p-benzenediol (C₁₁pPHCNa) has been studied. Two two-phase regions were observed, one was a wide region in the cationic surfactant-rich side and the other in the vicinity of R = 1:1, where R is the mixing mole ratio of DTAB to C₁₁pPHCNa in global solution. Multi-lamellar vesicles are formed in the concentrated upper phase of cationic surfactant-rich systems and spherical aggregates in the concentrated bottom phase at R = 1:1. The microstructure of the solution and the phase behavior of the aqueous two-phase system strongly depended on the total concentration and the composition of the system.     

The behaviour of drag-reducing cationic surfactant solutions

The behaviour of two types of drag reducing surfactant solutions was studied in turbulent flows in pipes of different diameters. Our surfactant systems contained rod-like micelles; they consisted of equimolar mixtures ofn-tetradecyltrimethylammonium bromide,n-hexadecyltrimethylammonium bromide, and sodium salicylate. The structure of the turbulence was studied using a laser-Doppler anemometer in a 50 mm pipe. In the turbulent flow regime both surfactant solutions exhibited characteristic flow regimes. These flow regimes can be influenced by changing the amount of excess salt, the surfactant concentration, or the temperature. Shear viscosity measurements in laminar pipe and Couette flows show the occurrence of the so-called shear-induced state, where the viscosity increases and the surfactant solution becomes viscoelastic. The shape of the turbulent velocity profile depends on the flow regime. In the turbulent flow regime at low Reynolds numbers, velocity profiles similar to those observed for dilute polymer solutions are found, whereas at maximum drag reduction conditions more S-shaped profiles that show deviations from a logarithmic profile occur. An attempt is made to explain the drag reduction by rod-like micelles by combining the results of the rheological and the turbulence structure measurements.     

Ceramic membrane ultrafiltration of anionic and nonionic surfactant solutions

The ultrafiltration of two types of surfactants, sodium dodecyl sulfate (SDS, anionic) and Tergitol NP-9 (nonylphenol polyethylene glycol ether, nonionic), using a 20 nm ZrO₂ tubular membrane was investigated. The influence of crossflow velocity, temperature, pressure, and surfactant concentration on the permeate flux, close to and above the critical micelle concentration (CMC), is reported. Permeate flux and surfactant retention were measured in order to evaluate concentration polarization and fouling phenomena, and also the variation of these parameters due to surfactant/membrane interactions. High surfactant retentions (60–70%) were achieved depending on the feed concentration.     

Spectroscopic investigations in molecularly organized solvent media. Part 3. Examination of the nitromethane selective quenching rule in aqueous anionic + cationic and anionic + nonionic mixed surfactant solutions

Applicability of the nitromethane selective quenching rule for discriminating between alternant versus nonalternant polycyclic aromatic hydrocarbons (PAHs) is examined for 20 representative PAH solutes dissolved in micellar sodium dodecylsulfate (SDS) + cetyltrimethylammonium bromide (CTAB), SDS + dodecyltrimethylammonium bromide (DTAB), SDS + Brij-35, and SDS + sodium octanoate (SO) mixed surfactant solvent media. Experimental results show that nitromethane quenched fluorescence of all 8 alternant PAHs studied in the four different solvent systems. Unexpected quenching behavior was observed, however, in the case of nonalternant PAHs. Nitromethane quenched fluorescence emission of nonalternant PAHs dissolved in the SDS + SO solvent media, which is contrary to the selective quenching rule. In the case of the mixed anionic + cationic surfactant solvent media, nitromethane quenching selectivity was restored at concentration ratios of approximately 4?:?1 (anionic:cationic) or less.     

Spectroscopic investigations in molecularly organized solvent media. Part 3. Examination of the nitromethane selective quenching rule in aqueous anionic + cationic and anionic + nonionic mixed surfactant solutions

Applicability of the nitromethane selective quenching rule for discriminating between alternant versus nonalternant polycyclic aromatic hydrocarbons (PAHs) is examined for 20 representative PAH solutes dissolved in micellar sodium dodecylsulfate (SDS) + cetyltrimethylammonium bromide (CTAB), SDS + dodecyltrimethylammonium bromide (DTAB), SDS + Brij-35, and SDS + sodium octanoate (SO) mixed surfactant solvent media. Experimental results show that nitromethane quenched fluorescence of all 8 alternant PAHs studied in the four different solvent systems. Unexpected quenching behavior was observed, however, in the case of nonalternant PAHs. Nitromethane quenched fluorescence emission of nonalternant PAHs dissolved in the SDS + SO solvent media, which is contrary to the selective quenching rule. In the case of the mixed anionic + cationic surfactant solvent media, nitromethane quenching selectivity was restored at concentration ratios of approximately 4 : 1 (anionic:cationic) or less. Received: 22 May 1997 / Revised: 29 September 1997 / Accepted: 3 October 1997     

Dual-opposite injection electrokinetic chromatography for the unbiased, simultaneous separation of cationic and anionic compounds

The concept of dual opposite injection in capillary electrophoresis (DOI-CE) for the simultaneous separation, under conditions of suppressed electroosmotic flow, of anionic and cationic compounds with no bias in resolution and analysis time, is extended to a higher pH range in a zone electrophoresis mode (DOI-CZE). A new DOI-CE separation mode based on electrokinetic chromatography is also introduced (DOI-EKC). Whereas conventional CZE and DOI-CZE are limited to the separation of charged compounds with different electrophoretic mobilities, DOI-EKC is shown to be capable of separating compounds with the same or similar electrophoretic mobilities. In contrast to conventional EKC with charged pseudostationary phases that often interact too strongly with analytes of opposite charge, the neutral pseudostationary phases appropriate for DOI-EKC are simultaneously compatible with anionic and cationic compounds. This work describes two buffer additives that dynamically suppress electroosmotic flow (EOF) at a higher pH (6.5) than in a previous study (4.4), thus allowing DOI-CZE of several pharmaceutical bases and weakly acidic positional isomers. Several DOI-EKC systems based on nonionic (10 lauryl ether, Brij 35) or zwitterionic (SB-12, CAS U) micelles, or nonionic vesicles (Brij 30) are examined using a six-component test mixture that is difficult to separate by CZE or DOI-CZE. The effect of electromigration dispersion on peak shape and efficiency, and the effect of surfactant concentration on retention, selectivity, and efficiency are described.     

双烃链正,负离子表面活性剂复合物水溶液的表面化学性质研究

本文研究了具有双烃链的正、负离子表面活性剂混合水溶液的表面和液相性质、。负离子表面活性剂是琥珀酸二己酯磺酸钠[简写为(C6)2SNa],正离子表面活性剂是氯化二正辛基羟乙基甲基铵[(C8)2NCl]和氯化辛基羟乙基二甲基铵[C8NCl]。为了增加复合物的溶解度,在铵基上引入了羟乙基。测定了表面张力-浓度关系,用GIBBS公式计算表面吸附量和吸附分子面积。结果表明,由于正、负表面活性离子之间的强烈相互作用,所研究的两种混合物体系的表面活性远高于单独的表面活性剂。在等摩尔混合和离子强度0.1mol/kg情况下,(C6)2SNa-(C8)2NCl体系的吸附层组成是对称的(摩尔比为1:1),且在临界胶团浓度(cmc)以上析出新相,表明此cmc实质上是复合物的溶解度;而(C6)2SNa-C8NCl体系的吸附层为不对称组成(摩尔比非1:1),在cmc以上可能形成相当大的胶团,两种体系混合溶液的起泡性有极大差异。     

Solubilization of phenols in anionic polyelectrolyte gels with adsorbed cationic surfactant

Solubilization isotherms for various phenols in cetylpyridinium chloride (CPC)-polyelectrolyte gel aggregates have been determined in order to compare solubilization within these aggregates with that in free micelles and to examine the effects of gel chemistry and structure on solubilization. The isotherms describing solubilization are quite similar to those found for free surfactant in solution. Solutes that are more hydrophobic give rise to larger solubilization constants with trends similar to what is seen for hydrophobic effects in adsorption from aqueous solutions onto hydrophobic solids. The solubilization constants decrease as the fraction of solute in the aggregates increases, indicating that the solutes partition into the palisade region of the aggregates. Solubilization is found to be quite insensitive to changes in gel structure (cross-linker varying from 1% to 3%) and chemistry (poly(acrylic acid) versus poly(methacrylic acid) and neutralization from 50% to 100%). However, the switch from poly(acrylic acid) to poly(methacrylic acid) did give rise to a slight decrease in magnitude of the slope of the isotherm. The most significant factors appear to be the initial concentration of surfactant in solution and the ratio of surfactant solution to gel amount. A decrease in surfactant concentration (especially combined with an increase in solution volume) gives rise to a decrease in solubilization constants.