Synergistic interactions in the mixed micelles of cationic gemini with zwitterionic surfactants: the pH and spacer effect

Mixed micelle formation of binary cationic gemini (12-s-12, s=4, 6) and zwitterionic (N-dodecyl-N,N-dimethylglycine, EBB) surfactants has been investigated by measuring the surface tension of aqueous solution as a function of total concentration at various pH values from acidic to basic, under conditions of 298.15 K and atmospheric pressure. The results were analyzed by applying regular solution theory (RST), and Motomura's theory, which allows for the calculation of the excess Gibbs energy of micellization purely on the basis of thermodynamic equations. The synergistic interactions of all the investigated cationic gemini + zwitterionic surfactants mixtures were found to be dependent upon the pH of the solution and the length of hydrophobic spacer of gemini surfactant. The evaluated excess Gibbs free energy is negative for all the systems.     

Forces between glass surfaces in mixed cationic-zwitterionic surfactant systems

We report atomic force microscopy (AFM) measurements of the forces between borosilicate glass solids in aqueous mixtures of cationic and zwitterionic surfactants. These forces are used to determine the adsorption of the surfactant as a function of the separation between the interfaces (proximal adsorption) through the application of a Maxwell relation. In the absence of cationic surfactant, the zwitterionic surfactant N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS) undergoes little adsorption to glass at concentrations up to about 2/3 critical micelle concentration (cmc). In addition, DDAPS does not have much effect on the forces over the same concentration range. In contrast, the cationic surfactant dodecylpyridinium chloride (DPC) does adsorb to glass and does affect the force between glass surfaces at concentrations much lower than the cmc. In the presence of a small amount of DPC (0.05 mM = cmc/300), the net force between the glass surfaces is quite sensitive to the solution concentration of DDAPS. A model-independent thermodynamic argument is used to show that the surface excess of DDAPS depends on the separation between the glass interfaces when the cationic surfactant is present and that the surface excess of the cationic surfactant is more sensitive to interfacial separation in the presence of the zwitterionic surfactant. The change in adsorption of the zwitterionic surfactant is explained in terms of an intermolecular coupling between the long-range electrostatic force acting on the cationic surfactant and the short-range hydrophobic interaction between the alkyl chains on the cationic and zwitterionic surfactants. The adsorptions of cationic and zwitterionic surfactants in mixtures were measured independently and simultaneously by attenuated total internal reflection infrared spectroscopy (ATR-IR). The adsorption of the zwitterionic surfactant is enhanced by the presence of a small amount of cationic surfactant.     

PHOTOPHYSICAL STUDY OF THE SCHIFF BASES OF 5'-DEOXYPYRIDOXAL AND n-HEXYLAMINE IN CATIONIC MICELLES

Abstract-The absorption and fluorescence spectra of the Schiff bases formed between 5'-deoxypyridoxal and n-hex-ylamine in aqueous media containing different concentrations of the cationic surfactant hexadecyltrimethylammonium bromide were recorded at 25°C. The quantum yields of fluorescence of the different zwitterionic and enol forms of the chemical species of the Schiff bases occumng in media of pH 4.5–8.5 were determined. Also, the fluorescence quenching resulting from the presence of the surfactant and that of iodide ion were analyzed. From the results obtained it follows that the zwitterionic forms do not interact with the cationic surfactant, whereas the enol forms do interact with it.     

Effects of Surfactants on Hydride Transfer from Methylene Blue Leucodye to 2,5-Dihydroxyl-1,4-benzoquinone in Aqueous Solution

The effects of monomeric surfactants on the hydride transfer from (one electron oxidation of) methylene blue leucodye to (by) 2,5-dihydroxy-1,4-benzoquinone in aqueous solution were investigated at 25°C using a stopped-flow spectrometer. The results indicated that cationic, anionic, and zwitterionic surfactants inhibited the reaction while nonionic surfactant showed no appreciable effect on the reaction. These observations are rationalized by electrostatic factors between surfactant monomer (or micelle) and reactant with charge or the charge transfer complex of the hydride transfer reaction. Above the cmc, the effects are treated quantitatively using a kinetic model.     

Two routes to vesicle formation: metal-ligand complexation and ionic interactions

Two routes to vesicle formation were designed to prepare uni- and multilamellar vesicles in salt-free aqueous solutions of surfactants. The formation of a surfactant complex between a double-chain anionic surfactant with a divalent-metal ion as the counterion and a single-chain zwitterionic surfactant with the polar group of amine-oxide group is described for the first time as a powerful driving force for vesicle-phases constructed from salt-free mixtures of aqueous surfactant solutions. As a typical example, a Zn(2+)-induced charged complex fluid, vesicle-phase has been studied in aqueous mixtures of tetradecyldimethylamine oxide (C(14)DMAO) and zinc 2,2-dihydroperfluorooctanoate [Zn(OOCCH(2)C(6)F(13))(2)]. This ionically charged vesicle-phase formed due to surfactant complexation has interesting rheological properties and is not shielded by excess salts because there are no counterions in the solution. Such a vesicle-phase of surfactant complex is important for many applications; for example, the vesicle-phase was further used to produce in situ the vesicle-phase of the salt-free cationic/anionic (catanionic) surfactants, C(14)DMAOH(+)-(-)OOCCH(2)C(6)F(13). The salt-free catanionic vesicle-phase could be produced through injecting H(2)S gas into the C(14)DMAO/Zn(OOCCH(2)C(6)F(13))(2) vesicle-phase, because the zwitterionic surfactant C(14)DMAO can be charged by the H(+) released from H(2)S to become a cationic surfactant and Zn(2+) was precipitated as ZnS. After the ZnS precipitates were removed from C(14)DMAO/Zn(OOCCH(2)C(6)F(13))(2) solutions, the final mixed solution does not contain excess salts as do other cationic/anionic surfactant systems. Both the C(14)DMAO-Zn(OOCCH(2)C(6)F(13))(2) complex and the resulting catanionic C(14)DMAOH(+)-(-)OOCCH(2)C(6)F(13) solution are birefringent Lalpha-phase solutions that consist of uni- and multilamellar vesicles. Ring-shaped semiconductor ZnS materials with encapsulated ZnS precipitates and regular spherical ZnS particles were prepared, which resulted in a transition from vesicles composed of metal-ligand complexes to vesicles held together by ionic interactions in the salt-free aqueous systems. This strategy should provide a new method to prepare inorganic materials. The present routes to form vesicles solve a problem: how to prepare nanomaterials using surfactant self-assembly, with structure controlled not by the growing material, but by the phase behavior of the surfactants.     

Synthesis of Mg2Al-Cl layered double hydroxide nanosheets in a surfactant-free reverse microemulsion

The synthesis of Mg₂Al-Cl layered double hydroxide (LDH) nanosheets in a surfactant-free reverse microemulsion is described. The microemulsion was composed of toluene, isopropanol, and an aqueous solution as the dispersed phase. An aqueous LDH nanosheet dispersion was obtained by a double-microemulsion technique. LDH nanosheets were characterized by X-ray powder diffraction, transmission electron microscopy, scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and thermogravimetric and elemental analyses. The LDH nanosheets consisted of a single brucite layer without any loading of organic molecules. To the best of our knowledge, this is the first report of a naked LDH monolayer aqueous dispersion being directly obtained. The LDH monolayers can be used as building blocks for LDH-based functional materials.     

Alkylation of carbonyl compounds in water: formation of C-C and C-O bonds in the presence of surfactants

The formation of C-C and C-O bonds by the reaction of enolate intermediates with electrophilic substrates commonly requires strong bases, aprotic solvents and very low temperatures. A way of performing the same reactions with sodium hydroxide at moderate temperatures in aqueous surfactant solutions is presented. Different halides, ketones and surfactants (cationic, zwitterionic and anionic) have been used. The results obtained show that the amount of ketone alkylation is much higher and that the reactions are faster in the presence than in the absence of surfactant aggregates. The hydrolysis of the halide is minimised in the presence of cationic or zwitterionic surfactants.     

Use of surfactant-mediated phase separation (cloud point extraction) with affinity ligands for the extraction of hydrophilic proteins

The feasibility of utilizing a zwitterionic surfactant, 3-(nonyldimethylammonio)propylsulfate, or nonionic surfactant, Triton X-114, mediated phase separation in conjunction with affinity ligands was studied for hydrophilic protein extractions. Below (or above) its critical temperature (so-called cloud point), aqueous solutions of zwitterionic (or nonionic) surfactants separate into two immiscible phases, a surfactant-rich phase and an aqueous phase. Avidin was successfully extracted into the zwitterionic surfactant-rich phase when a small amount of the affinity ligand, N- biotinoyl)dipalmitoyl- l -alpha- phosphatidyl ethanolamine, was added to the system. It was not possible to extract hexokinase into the surfactant-rich phase of the nonionic surfactant, Triton X-114, even if a considerable amount of octyl-beta-d-glucoside was added to the solution as an affinity ligand. In contrast, the use of the zwitterionic surfactant and octyl-beta-d-glucoside as an affinity ligand proved to be effective for the extraction of hexokinase. The hexokinase extraction efficiency was found to depend upon the solution pH and the concentration of the affinity ligand in the system. The results clearly indicate that hydrophilic proteins can be successfully extracted with surfactant mediated phase separations (cloud point extractions) via use of the zwitterionic surfactant, 3-(nonyldimethylammonio)propylsulfate, and appropriate affinity ligands. Some advantages of zwitterionic surfactants in such extractive processes relative to that of nonionic surfactants are delineated.     

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.     

pH reversible micelle transition of a tertiary amine-based gemini surfactant in aqueous solution

In this work, we prepared a tertiary amide-based gemini surfactant (DSTAPA), which contained two pH-sensitive tertiary amide head groups. Then the molecule state distribution and self-assembly transition of the surfactant in aqueous solution were investigated under different pH conditions. The DSTAPA molecules were on the states of double cationic (DSTAPAH²⁺), single cationic (DSTAPAH⁺), and double tertiary amine groups (DSTAPA) under acidic, neutral, and basic conditions, respectively. With the variation of the molecule states, the sample was water-like below pH of 6.8 and immediately transformed to gel-like fluid between pH of 6.8 and 7.8, then changed to white precipitate with the further increase of pH value. Furthermore, the microstructure and regulation mechanism were investigated by rheological measurements, dynamic light scattering, and cryogenic transmission electron microscopy. The appearance and micelle transitions of the DSTAPA aqueous solution are actually owing to the spherical–worm-like micelle transition, leading to dramatic viscosity increase and hydrogel formation. This transition was completely reversible and repeated for at least three cycles. Finally, a reasonable mechanism of the transition was proposed based on the viewpoints of the molecular states and micelle structures. The DSTAPA aqueous system with pH-reversible property has a great potential application in oil and gas production.     

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.     

Interaction of surfactants and aminoindophenol dye

The interaction of dye and surfactants was studied by their spectroscopic and surface properties. Large bathochromic shift (15 nm) in the absorption spectrum was found for aminoindophenol dye at high pH in cationic surfactant, while there is no significant shift in anionic, zwitterionic and nonionic surfactant solutions. The static and dynamic surface properties show there is strong interaction in mixture of cationic surfactant and aminoindophenol dye. Interaction of dye and surfactants on surface and in solution is correlated to the intensity of dye deposition on fiber. The charge complex formation between cationic surfactant and aminoindophenolic dye delays the dye diffusion into keratin fiber. The stronger is the dye/surfactant interaction, the lower dye deposition and diffusion become.     

Triton X-100六角液晶相中制备镁铝层状双金属氢氧化物纳米片及其药物载体应用

以Triton X-100 六角相溶致液晶作微反应器, 采用共沉淀法制备了镁铝层状双金属氢氧化物(LDHs)纳米薄片(L-LDHs). 以双氯芬酸钠(DS)为药物模型分子, 采用离子交换法制备了DS插层LDHs (DS/L-LDHs)纳米杂化物, 在37.0 ℃、pH=7.2的缓冲溶液中, 考察了纳米杂化物的药物释放性能, 并与传统溶液共沉淀法制备的镁铝LDHs (S-LDHs)纳米片状颗粒进行了对比. 采用粉末X射线衍射(XRD)、傅里叶变换红外(FT-IR)光谱、场发射扫描电镜(FE-SEM)、透射电镜(TEM)和N₂吸附-脱附等技术对所制备的LDHs和DS/LDHs 样品的晶体结构、比表面积、形貌特征等进行了表征. 结果表明, L-LDHs比S-LDHs具有更低的片厚度, 更高的比表面积和药物负载量, 所形成的DS/L-LDHs纳米杂化物药物释放速率也明显低于DS/S-LSHs, 即L-LDHs更适于作药物载体. DS/L-LDHs纳米杂化物的药物释放过程符合准二级动力学方程, 受颗粒内部扩散过程控制. 溶致液晶模板法可实现LDHs的形貌可控制备, 为LDHs基功能材料的研发提供了新途径.     

Adsorption Isotherms of Cetylpyridinium Chloride with Iron III Salts at Air/Water and Silica/Water Interfaces

The interaction of iron III salts and cetylpyridinium chloride (CPC) has been studied at the air/water and silica/water interfaces. The surface tension of cetylpyridinium chloride has been determined in aqueous solutions in the presence of iron III chloride and iron III nitrate at two constant pH values, namely, 3.5 and 1.2. It is shown that the surface tension of the cationic surfactant depends upon the ionic strength of the solution through the pH adjustment in the presence of the former salt but not in the presence of the latter. The effect of iron III nitrate on the surface tension of CPC is similar to that of potassium nitrate, indicating that the iron III various-hydrolyzed species do not interfere with the composition of the air/water interface. The competitive adsorption of iron III nitrate salt and the cationic surfactant at a silica/water interface was next investigated. The adsorption isotherms were determined at pH 3.5. It is shown that although the iron III ions, which were added to the silica dispersion in the presence of the cetylpyridinium ions, were strongly bound to the anionic surface sites, the surfactant ions are not salted out in the solution but remain in close vicinity of the silica surface. Conversely as the cationic surfactant is added first to the silica dispersion in the presence of the adsorbed iron III ions, the metal ions and the surfactant ions are both coadsorbed onto the silica surface. It is suggested that iron III hydrolyzed or free cations and the cationic surfactant molecules may not compete for the same adsorption sites onto the silica surface.     

Synthesis and aqueous solution properties of homologous gemini surfactants with different head groups

A series of homologous gemini surfactants possessing identical hydrophobic chains but different ionic head groups (cationic, anionic, zwitterionic) were synthesized, and their aqueous solution properties were examined. The results showed that the surface activities of gemini surfactants are superior to those of corresponding conventional monomeric surfactants, and molecular arrangements of gemini surfactants at the air-water interface are tighter than those of corresponding conventional surfactants. It was also found that zwitterionic gemini surfactant possesses the highest surface activity among the three surfactants. The behavior at the air-water interface is closely related to the molecular structural features of surfactants, which provide an indication for synthesizing highly-efficient surfactants.      

阳离子和两性表面活性剂在聚甲基丙烯酸甲酯表面的吸附行为

利用座滴法研究了阳离子表面活性剂十六烷基醚羟丙基季铵盐(C₁₆PC)、十六烷基聚氧乙烯醚羟丙基季铵盐(C₁₆(EO)₃PC)和两性离子表面活性剂十六烷基醚羟丙基羧酸甜菜碱(C₁₆PB)、十六烷基聚氧乙烯醚羟丙基羧酸甜菜碱(C₁₆(EO)₃PB)溶液在聚甲基丙烯酸甲酯(PMMA)表面上的润湿性质, 考察了表面活性剂类型及浓度对接触角的影响趋势. 研究发现: 低浓度条件下表面活性剂分子可能以平躺的方式吸附到固体界面, 且亲水基团靠近固体界面, PMMA表面被轻微疏水化; 在高浓度时则通过Lifshitz-van der Waals 作用吸附, 亲水基团在外, PMMA表面被亲水改性. 聚氧乙烯基团(EO基团)的引入对阳离子表面活性剂的接触角影响不大; 而含有聚氧乙烯基团的两性离子表面活性剂在PMMA界面上以类似半胶束的聚集体吸附, 大幅度降低接触角.     

Microfiltration of amphoteric surfactant using ceramic membranes

The microfiltration of commercially available amphoteric surfactant using ceramic membranes has been investigated. Various combinations operating conditions such as pH, electrolyte and surfactant concentrations were employed. Zeta potential and adsorption isotherms were obtained for the components of membrane surfactant system as functions of pH using surfactant or indifferent electrolyte (KCl). The shift in the membrane isoelectric point induced by the surfactant is linked to the carboxylic groups present on the surfactant which are believed to play a dominant role in the net surface charge of the membrane. A minimum in the permeate flux was found at the pH corresponding to the isoelectric point of the zwitterionic surfactant. This behaviour is ascribed to the interactions occurring between the surfactant–surfactant molecules and the surfactant–membrane. The higher fluxes obtained at low pH as compared to high pH arise from different fouling mechanisms and ionic strengths. Lower fluxes were found when inorganic electrolytes were used in conjunction with surfactant. However, as the valency of the salt increases, flux behaviour of the zwitterionic surfactant (close to isoelectric point) does not vary whilst the cationic and anionic state of the surfactants are much more affected. Interactions between surfactant molecules as a result of the charge screening effects by the larger valence ions are encouraged. The permeate flux declines with an increasing surfactant concentration even though some concentrations fall under the critical micelle concentration (c.m.c.). This is attributed to concentration polarisation in which the accumulated surfactant concentration at the membrane surface could form a stable viscous phase which is resistant to permeate flow in the secondary layer next to the membrane surface. This paper demonstrates the role interactions such as surfactant–surfactant and surfactant–membrane play in influencing the filterability of surfactant solutions using ceramic membranes.     

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.     

Kinetics of alkaline fading of methyl violet in micellar solutions of surfactants: Comparing Piszkiewicz's,Berezin's,and pseudophase ion-exchange models

The micellar effect of surfactants of various types on the rate of the reaction between methyl violet and hydroxide ion is studied. The absorption spectra show that the cation of methyl violet is bound by micelles of all types at proper concentrations of surfactants. The observed rate constant in micellar systems containing nonionic Brij-35, zwitterionic 3-(dimethyldodecylammonio)-propanesulfonate, cationic cetyltrimethylammonium bromide and hydroxide surfactants is higher, whereas in solutions of the anionic surfactant sodium dodecylsulfate is lower than that one in the surfactant-free system. Piszkiewicz's, Berezin's, and pseudophase ion-exchange models of the kinetic micellar effect are used for the treatment of the dependences of the above-mentioned constants on the surfactant concentration. The values of the corresponding kinetic parameters are compared and discussed. The influence of nonionic, zwitterionic, and anionic micelles on the reaction rate is discussed on the basis of medium and concentration kinetic effects. The character of the cationic micelles effect is somewhat paradoxical. Although the observed pseudo–first-order reaction rate constant substantially increases in the presence of such micelles, the second order-rate constant in these micelles is lower than the corresponding value in surfactant-free aqueous solution. As a possible explanation, the decrease in the reactivity of the HO^– ions is proposed, owing to their electrostatic association with the cationic headgroups (“diverting effect”).     

Aqueous Electrochemistry of Anthraquinone and Its Correlation with the Dissolved States of a Cationic Surfactant

Cyclic voltammetry was employed to study the electrochemical behavior of anthraquinone (AQ) in aqueous solution at a glassy carbon electrode using the sodium salt of anthraquinone-2-sulphonic acid (AQS). The cyclic voltammograms show a reduction wave and a corresponding oxidation wave. The electrochemical reaction of AQ in aqueous solution involves a two electron transfer process followed by a coupled chemical reaction and exhibits strong pH dependence at low pH (<4). A satellite peak is also observed at the cathodic side of the reduction wave for the reduction of the sulfonate group of AQS. The electrochemical investigation was also carried out in the presence of a cationic surfactant, cetyltrimethylammonium bromide (CTAB). Similar redox behavior can be observed for the electrochemical reaction of AQS in the presence of CTAB solutions similar to the aqueous media. The electrochemical responses have been found to depend on the dissolved states of the surfactant. The current-potential behavior of AQS depends on the concentration of CTAB and micellization has a profound effect on the electrochemical behavior of AQ.