Structure and physico-chemical properties in mixed aqueous solution of sodium alkvicarboxylate-alkyltrimethylammonium bromide

The physico-chemical properties of organized assemblies (micelle or vesicle ) from sodium alkylcarboxylate - alkyltrimethyl -ammonium bromide mixture have been investigated systematically. In different mixed cationic-anionic surfactant systems, micelles and vesicles can coexist or be transformed into each other on different conditions. The experimental results are explained prelimilarily from the viewpoint of molecular packing geometry. The solubilization of organic compound in the mixed surfactant system was also studied in detail.     

Effect of alcohols on the micellar properties in aqueous solution of alkyltrimethylammonium bromides

The effect ofn-butanol,n-propanol, andn-hexanol on the critical micelle concentration (CMC) and degree of ionisation of the micelles of dodecyl-, tetradecyl- and hexadecyltrimethylammonium bromides in aqueous solution has been determined by conductimetric techniques. Increase of the molality of added alcohol over the concentration ranges examined (up to 0.3 mol kg^–1 butanol, 0.07 mol kg^–1 pentanol and 0.025 mol kg^–1 hexanol) caused a progressive decrease of CMC and increase of the degree of ionisation for each surfactant-alcohol system. At a constant molality of added alcohol the degree of ionisation increased with a) an increase of the chain length of the surfactant for each alcohol and b) an increase of the chain length of the alcohol for each surfactant. The distribution of each alcohol between the aqueous and micellar phases and the free energy of solubilization were determined from the change of CMC with molality of added alcohol.     

Formation and coexistence of the micelles and vesicles in mixed solution of cationic and anionic surfactant

In the aqueous mixtures of sodium alkylcarboxylate and alkyltrimethylammonium bromide, large unilamelar vesicles can be formed spontaneously or by sonication as the total carbon number in the HC chains is 19 (or larger). Vesicle formation can be influenced by changes of pH, molar ratio of the two surfactant components, and the polar head group of cationic surfactant. Micelles may coexist with the vesicles in these mixed systems. The larger hydrodynamic radius (200 nm) and aggregation number (800) illustrate that the shape of the micelle in 1:1 C₉H₁₉COONa–C₁₀H₂₁N(CH₃)₃Br is rod-like. In some mixed systems, the micelles can be transformed into stable vesicles by sonication — a phenomenon revealed for the first time. The surface-chemical properties of these catanionic surfactant solutions and the stabilities of vesicle have been studied systematically.     

阴离子Gemini表面活性剂和阳离子传统表面活性剂混合体系双水相中囊泡形貌的转变

通过电子显微镜观察了阴离子gemini表面活性剂C₁₁- p-PhCNa和阳离子传统表面活性剂DTAB混合体系双水相中囊泡形貌随体系组成和浓度的转变。结果表明,双水相较浓的一相中形成了多层囊泡,囊泡的大小和壁厚随相的组成和浓度而改变,两组分等电荷混合有利于形成较大且壁较厚的囊泡。分析表明, gemini表面活性剂在聚集体中采取的反式构象可能是其容易形成厚壁多层囊泡的重要原因,C₁₁- p-PhCNa联接链上的苯氧基与DTA⁺之间的p-阳离子相互作用以及两组分相反电性头基之间的静电吸引使囊泡壁的多层结构更加稳定。     

Phase behavior in mixtures of cationic and anionic surfactants in aqueous solutions

Phase behavior of cationic/anionic surfactant mixtures of the same chain length (n=10, 12 or 14) strongly depends on the molar ratio and actual concentration of the surfactants. Precipitation of catanionic surfactant and mixed micelles formation are observed over the concentration range investigated. Coacervate and liquid crystals are found to coexist in the transition region from crystalline catanionic surfactant to mixed micelles.The addition of oppositely charged surfactant diminishes the surface charge density at the mixed micelle/solution interface and enhances the apparent degree of counterion dissociation from mixed micelles. Cationic surfactants have a greater tendency to be incorporated in mixed micelles than anionic ones.     

Chemical equilibrium model for the thermodynamic properties of mixed aqueous micellar systems: Application to thermodynamic functions of transfer

Mixed micelles can be formed in water between various pairs of hydrophobic solutes such as surfactants, alcohols and hydrocarbons. These systems can often be studied through the thermodynamic functions of transfer of one of the solutes, usually kept near infinite dilution, from water to an aqueous solution of the other solute. When mixed micelles are formed, these functions change significantly, and often go through extrema, in the region where the binary system micellizes or undergoes some microphase transition.Three main effects are responsible for the observed trends: pair-wise interactions between both solutes in the monomeric form, a distribution of the reference solute between the aqueous and micellar phases and a shift in the monomer-micelle equilibrium in the vicinity of the reference solute. Simple equations can be derived for these three effects which can account for the sign and magnitude of the observed trends using parameters which are derived for the most part from the two binary systems.     

Rheological and thermo-responsive characteristics of the mixed aqueous solution of gemini cationic surfactant and hydroxyl naphthalene carboxylic acid sodium

The new thermo-switchable wormlike micellar systems were developed by mixing the gemini cationic surfactant, 2-hydroxypropyl-1,3-bis (dimethylmyristylammonium chloride) (14-3(OH)-14(2Cl) and sodium 1-hydroxynaphthalene-2-carboxylate (1SHNC) and sodium 2-hydroxynaphthalene- 3-carboxylate (2SHNC) in a certain concentration range. Their viscoelastic and thermos-responsive behaviors as a function of the salts concentration or temperature were investigated via rheological and cryo-TEM investigations. The results demonstrated that the zero-shear viscosity (η₀) significantly increased while raising salt concentrations above a threshold concentration (C_S*) until reaching maximum and then decreased. For the mixed solutions before the maximum, the zero-shear viscosity linearly decreased with increasing temperature and conformed to the Arrhenius law. However, for those mixed systems displaying thermo-responsive characteristic after the summit, the curve of η₀ as a function of temperature exhibited a maximum over the whole temperature range, namely, the systems showed thermo-thickening and thermo-thinning behaviors at low and high temperatures. The abovementioned phenomena were explained by the formation of hydrogen bond in 14-3(OH)-14(2Cl) molecules and the different solubility of SHNC under different temperatures, and the transition mechanisms of the aggregates were analyzed accordingly.     

Rheological properties of the aqueous solution for fluorocarbon‐containing hydrophobically modified sodium polyacrylic acid with various surfactants

The interaction of fluorocarbon‐ containing hydrophobically modified sodium polyacrylic acid (FMPAANa) (0.5 wt%) with various surfactants (anionic, nonionic and cationic) has been investigated by rheological measurements. Different rheological behaviors are displayed for ionic surfactants and nonionic surfactants. Fluorinated surfactants have stronger affinity with polyelectrolyte hydrophobes comparing with hydrogenated surfactants. The hydrophobic association of FMPAANa with a cationic surfactant (CTAB) and a fluorinated nonionic surfactant (FC171) is much stronger than with a nonionic surfactant (NP7. 5) and an anionic surfactant (FC143). Further investigation of the effects of temperature on solution properties shows that the dissociation energy E_m is correlated to the strength of the aggregated junctions.     

Synthesis of poly(n‐hexyl isocyanate‐b‐N‐vinylpyrrolidone) block copolymers by the combination of anionic and nitroxide‐mediated radical polymerizations: Micellization properties in aqueous solutions

A combination of anionic and nitroxide‐mediated radical polymerizations (dual initiator) was employed for the synthesis of poly(n‐hexyl isocyanate‐b‐N‐vinylpyrrolidone) (PHIC‐b‐PNVP) block copolymers. The samples were characterized with a size exclusion chromatograph equipped with refractive‐index and light scattering detectors as well as ¹H NMR spectroscopy. Relatively good control over the molecular weights was achieved. However, rather broad molecular weight distributions were obtained. The micellar properties of the PHIC‐b‐PNVP block copolymers were studied in water, which is a selective solvent for the poly(N‐vinylpyrrolidone) blocks. Static and dynamic light scattering revealed the presence of equilibrium between the micelles and clusters. The clusters partially deaggregated with increasing temperature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5719–5728, 2006     

Enthalpy of dilution of aqueous sodium chloride from 76 to 225°C and aqueous dodecyltrimethylammonium bromide from 50 to 225°C

Enthalpies of dilution of aqueous sodium chloride from 3.0 to about 0.01 mol-kg^–1 have been measured from 349.2 to 498.2 K near the saturation pressure of water using a flow calorimeter. Enthalpies of dilution of aqueous dodecyltrimethylammonium bromide have been measured from 0.3 to about 0.005 mol-kg^–1 and from 323.4 to 498.3 K, also near the saturation pressure of water.     

Self aggregation of binary mixtures of sodium dodecyl sulfate and polyoxyethylene alkyl ethers in aqueous solution

The mixed micelles of sodium dodecyl sulphate (SDS) with Brij35 and Brij 97 were studied separately by fluorescence measurement using pyrene as fluorescent probe. In the range of 0–1.0 mole fraction (X) of added SDS to Brij solutions, the cmc value of the mixed micelles varies from 0.085 to 8 mmol with Brij 35 and 0.04 to 8 mmol with Brij 97. The aggregation number also changes. A measure of the stability of mixed micelles is also presented. The interaction parameter ₁₂ and the chain–chain contribution parameter (B₁) are extracted from the analysis of the results. This parameter B₁ is related to the standard free energy change associated with the introduction of one ionic species into a nonionic micelle coupled with the release of one nonionic species from the micelle. The clouding behaviour of Brij 97 in the presence of SDS was investigated and the associated thermodynamic parameters of clouding were generated and discussed.     

Vesicle formation in aqueous mixture of the cetyltrimetylammonium bromide and an anionic chitosan derivative

The present work aimed at research the physic-chemical properties of the interaction of N-decyl-O-chitosan sulfate (an amphiphilic chitosan derivative, C₁₀-OCHS) with cetyltrimetylammonium bromide (CTAB) by the steady-state fluorescent, static/dynamic surface tension, turbidity and transmission electron microscopy (TEM). The results showed that the complex of C₁₀-OCHS/CTAB had high surface activity and lower critical aggregation concentration. Besides, the C₁₀-OCHS/CTAB could self-assemble into various aggregates like irregular spherical aggregates, vesicles or polydisperse aggregates from lower to higher concentrations of CTAB with a mixed C₁₀-OCHS concentration of 200?mg/L.     

Self diffusion and viscoelasticity of elongated micelles from cetyltrimethyl-ammonium bromide in aqueous sodium salicylate solution. II. Temperature effect

Forced Rayleigh scattering and dynamic viscoelastic experiments are performed to study slow global motions of networks formed by elongated micelles from cetyltrimethylammonium bromide (CTAB) in aqueous sodium salicylate (NaSal) solutions at six temperatureT from 25° to 60°C. The CTAB concentrationC _D of the solutions is fixed atC _D=0.01 M and a ratio of salt concentrationC _s toC _D is varied from 1 to 41. The self-diffusion coefficientD of the dye-labeled cetyldimethylamine incorporated in the micelles shows a complicatedC _s/C _D dependence with a maximum that is followed by a minimum at lower temperatures, but these two extremes gradually disappear with increasingT. TheC _s/C _D dependencies of both the steady-state viscosity and the terminal relaxation time are found consistent with the diffusion behaviour. TheD of all solutions tested monotonically increases withT, but shows different functional dependence onT asC _s/C _D varies. The applicability of the theory of Brownian motion of a rigid rod in the semidilute regime is examined usingD and values.     

Enthalpies of solution and dilution of butanol and pentanol in dodecyltrimethylammonium bromide micellar solutions

The enthalpies of solution and of dilution of 1-butanol and 1-pentanol were measured in micellar solutions of dodecyltrimethylammonium bromide by systematically changing the concentration of alcohols and surfactant. The enthalpies of solution at infinite dilution of alcohols at each surfactant concentration were evaluated from a linear plot. This quantity increases with surfactant concentration (up to 0.8m) with a curvature which depends on the alcohol alkyl chain length. The difficulties arising for a quantitative treatment of both the enthalpies of dilution and of solution at finite alcohol concentrations are discussed. The dependence on the surfactant concentration of the standard enthalpies of solution and the enthalpies of dilution for m0 are rationalized. From the resulting equations the distribution constant, standard enthalpy of transfer, standard enthalpy of solution, and the alcohol-alcohol interaction parameter in the micellar phase are evaluated. The enthalpies of transfer obtained using this technique agree well with those previously reported from enthalpies of mixing. The distribution constants also agree with those reported in the literature from several approaches: mixing enthalpies, partial molar volumes, and the dependence of the cmc on added alcohol.     

Synthesis and characterization of polyaniline‐multiwalled carbon nanotube nanocomposites in the presence of sodium dodecyl sulfate

Polyaniline‐carboxylic acid functionalized multi‐walled carbon nanotube (PAni/c‐MWNT) nanocomposites were prepared in sodium dodecyl sulfate (SDS) emulsion. First, the c‐MWNTs were dispersed in SDS emulsion then the aniline was polymerized by the addition of ammonium persulfate in the absence of any added acid. SDS forms the functionalized counterion in the resulting nanocomposites. The content of c‐MWNTs in the nanocomposites varied from 0 to 20 wt%. A uniform coating of PAni was observed on the c‐MWNTs by field‐emission scanning electron microscopy (FESEM). The PAni/c‐MWNT nanocomposites have been characterized by different spectroscopic methods such as UV‐Visible, FT‐Raman, and FT‐IR. The UV‐Visible spectra of the PAni/c‐MWNT nanocomposites exhibited an additional band at around 460 nm, which implies the induced doping of the MWNTs by the carboxyl group. The FT‐IR spectra of the PAni/c‐MWNT nanocomposites showed an inverse intensity ratio of the bands at 1562 and 1480 cm^?1 as compared to that of pure PAni, which reveals that the PAni in the nanocomposites is richer in quinoid units than the pure PAni. The increase in the thermal stability of conductivity of the nanocomposites was due to the network structure of nanotubes and the charge transfer between the quinoid rings of the PAni and the c‐MWNTs. Copyright © 2008 John Wiley & Sons, Ltd.     

Cationic Surfactants as Regulators in Paper Separation of 2‐Nitrophenol and 2,4,6‐Trinitrophenol in Water

The chemical pollutants 2‐nitrophenol (2‐NP) and 2,4,6‐trinitrophenol (2,4,6‐TNP) were studied for their separation from water by the paper capillary permeation adsorption technique by the use of the four cationic surfactants dodecyltrimethylammonium chloride (DTAC), tetradecyltrimethylammonium bromide (TTAB), cetyltrimethylammonium bromide (CTAB), cetylpyridinium chloride (CPC) as regulators. The effect of pH and the concentration of surfactant on the separatability have been investigated. A nearly 100% separatability was obtained for each pollutant at its optimum pH and surfactant concentration. It was shown that the separation was accomplished via surface adsorption onto the fibers of paper. The change in separatability at basic pH 11 with surfactant variety was analyzed. The result shows that the surfactant with a longer chain alkyl group is more effective for the separation of 2‐NP and the surfactants with 16 carbons in the long chain alkyl group are most effective. The surfactants with 12 carbons or more in the long alkyl group but containing no aromatic group such as pyridyl group are equally effective for accomplishing an efficient separation of 2,4,6‐TNP. Selective separation of 2‐NP from an admixture of 2‐NP plus 2,4,6‐TNP was attempted. The optimum surfactant for each pollutant was tested with seawater for removing the pollutant. The goal of this study is to search for an optimum cationic surfactant and optimum separation conditions for nitrophenols.     

Fabrication of polyaniline‐coated halloysite nanotubes by in situ chemical polymerization as a solid‐phase microextraction coating for the analysis of volatile organic compounds in aqueous solutions

We have synthesized an organic–inorganic polyaniline–halloysite nanotube composite by an in situ polymerization method. This nanocomposite is immobilized on a stainless‐steel wire and can be used as a fiber coating for solid‐phase microextraction. It was found that our new solid‐phase microextraction fiber is an excellent adsorbent for the extraction of some volatile organic compounds in aqueous samples in combination with gas chromatography and mass spectrometry. The coating can be prepared easily, is mechanically stable, and exhibits relatively high thermal stability. It is capable of extracting phenolic compounds from water samples. Following thermal desorption, the phenols were quantified by gas chromatography with mass spectrometry. The effects of extraction temperature, extraction time, sample ionic strength, stirring rate, pH, desorption temperature and desorption time were studied. Under optimal conditions, the repeatability for one fiber (n = 5), expressed as the relative standard deviation, is between 6.2 and 9.1%. The detection limits range from 0.005 to 4 ng/mL. The method offers the advantage of being simple to use, with a shorter analysis time, lower cost of equipment and higher thermal stability of the fiber in comparison to conventional methods of analysis.     

Novel Synthesis of 1H‐Inden‐1‐Ones and Thienylpropenones in Aqueous Medium

Condensation of acetylacetone with 4‐methoxybenzaldehyde, 2,4‐dimethoxybenzaldehyde, 3,4‐dimethoxybenzaldehyde, 4‐nitrobenzaldehyde and 2,4‐dinitrobenzaldehyde in water and in the presence of cetyltrimethylammonium bromide (CTABr) as cationic surfactant in dilute sodium hydroxide at room temperature did not afford the expected arylideneacetylacetone but yielded 1H‐inden‐1‐one derivatives 1 , while, with piperonaldehyde under the same conditions afforded dipiperonylideneacetone 2 . Also 3‐acetylthiophene condensed with some aromatic aldehydes under the same conditions gave the expected stereoselective thienylpropenones 4 . The structures of the products were identified by IR, NMR, Mass spectral data and elemental analysis.     

Enthalpy of solution of phenoxyalcohols solubilized in aqueous sodium dodecylsulfate and hexadecyltrimethylammonium bromide solutions

The enthalpy of solution of phenoxy 2-ethanol, 1 phenoxy,-3 propanol and benzylalcohol was determined at 25 °C in aqueous sodium dodecylsulfate and hexadecyltrimethylammonium bromide solution, up to 0.2 mol/kg surfactant concentration. Using the pseudo-phase model, the standard enthalpy of transfer and the partition coefficient of the alcohols between micelle and water are calculated. The latter quantity is found to be systematically larger when derived from enthalpy than from free energy measurements. Using the so-called compensation plot, the solution thermodynamics of aromatic and aliphatic alcohols in aqueous sodium dodecylsulfate and in the octane+water systems are compared. Aromatic alcohols display an anomalous behavior in the octane+ water system but not in the micellar one.The standard enthalpy of solution of various alcohols presents, when plotted against hexadecyltrimethylammonium bromide concentration, a shoulder in the region around 0.05 mol/kg; a discussion is presented on the evidence for alleged micellar structural changes in aqueous micellar systems.     

Bulk and microscopic properties of copolymer networks in mixed aqueous solvents

Amphiphilic films and hydrogels have been prepared from ethanol/water solutions containing a hydrocarbon-grafted water-soluble cellulose ether. These materials are characterized by dispersed hydrophobic microdomains which form spontaneously in the solvent due to the inherent incompatibility of the side chains with water. At low applied shear stress, the microdomains behave as temporary linkages of finite lifetimes, imparting viscoelastic properties to the networks. The molecular weight between microdomains was found to be independent of the volume fraction of polymer in the gel, and the number of linkages per backbone ranges from 22.8 ± 1.3 to 26.2 ± 1.5 over the frequency range 30–50 rad/s. The behavior of the solutions and gels was characterized using fluorescence and dynamic rheological measurements. It was demonstrated that the microdomains are capable of sequestering water-insoluble solutes. © 1992 John Wiley & Sons, Inc.