Mutual influence of cetyltrimethylammonium bromide and Triton X-100 on their adsorption at the water–air interface

On the basis of surface tension values of the aqueous solution of cetyltrimethylammonium bromide (CTAB) and Triton X-100 (TX-100) mixtures measured at 293 K as a function of CTAB or TX-100 concentration at constant TX-100 or CTAB concentration, respectively, the real surface area occupied by these surfactants at the water–air interface was established which is inaccessible in the literature. It appeared that at the concentration of the CTAB and TX-100 mixture in the bulk phase corresponding to the unsaturated monolayer at the water air-interface this area is the same as in the monolayer formed by the single surfactant at the same concentration as in the mixture. In the saturated mixed monolayer at this interface the area occupied by both surfactants is lower than that in the single surfactant monolayer corresponding to the same concentration in the aqueous solution. However, the decrease of the CTAB adsorption is lower than that of TX-100 and the total area occupied by the mixture of surfactants is also lower than that of the single one. The area of particular surfactants in the mixed saturated monolayer changes as a function of TX-100 and CTAB mixture concentration and at the concentrations close to CMC or higher the area occupied by both surfactants is the same. The changes of the composition of the mixed surface monolayer are connected with the synergetic effect in the reduction of the water surface tension by the adsorption of CTAB and TX-100 at the water–air interface. This effect was confirmed by the values of the standard Gibbs free energy of adsorption of both individual surfactants and their mixtures with different compositions in the bulk phase determined by using the Langmuir equation if RT instead of nRT was applied in this equation.     

Kinetics of metribuzin degradation by colloidal manganese dioxide in absence and presence of surfactants

The kinetics of the degradation of metribuzin by water-soluble colloidal MnO₂ in acidic medium (HClO₄) were studied spectrophotometrically in the absence and presence of surfactants. The experiments were performed under pseudo-first-order reaction conditions in respect of MnO₂. The degradation was observed to be of the first order in respect of MnO₂ while of fractional order for both metribuzin and HClO₄. The rate constant for the degradation of metribuzin was observed to decrease as the concentration of MnO₂ increased. The anionic surfactant, sodium dodecyl sulphate (SDS), was observed to be ineffective whereas the non-ionic surfactant, Triton X-100 (TX-100), accelerated the reaction rate. However, the cationic surfactant, cetyltrimethyl ammonium bromide (CTAB), caused flocculation with oppositely-charged colloidal MnO₂; hence further study was not possible. The catalytic effect of TX-100 was discussed in the light of the available mathematical model. The kinetic data were exploited to generate the various activation parameters for the oxidative degradation of metribuzin by colloidal MnO₂ in the absence as well as the presence of the non-ionic surfactant, TX-100.     

Interaction of Nonionic Surfactant Triton-X-100 with Ionic Surfactants

The interaction in two mixtures of a nonionic surfactant Triton-X-100 (TX-100) and different ionic surfactants was investigated. The two mixtures were TX-100/sodium dodecyl sulfate (SDS) and TX-100/cetyltrimethylammonium bromide (CTAB) at molar fraction of TX-100, α_TX-100 = 0.6. The surface properties of the surfactants, critical micelle concentration (CMC), effectiveness of surface tension reduction (γ_CMC), maximum surface excess concentration (Γ_max), and minimum area per molecule at the air/solution interface (A _min) were determined for both individual surfactants and their mixtures. The significant deviations from ideal behavior (attractive interactions) of the nonionic/ionic surfactant mixtures were also determined. Mixtures of both TX-100/SDS and TX-100/CTAB exhibited synergism in surface tension reduction efficiency and mixed micelle formation, but neither exhibited synergism in surface tension reduction effectiveness.     

Quenching of zinc phthalocyanine excited states by viologen surfactant assemblies——The influence of microenvironment

A series of functional surfactants of N-alkyl-N'-butyl viologens has been synthesized.The quenching of excited singlet and triplet states of zinc phthalocyanine was studied in DMSOand in mixed micelles containing the functional surfactant as one and cationic cetyl trimethylam-monium bromide(CTAB),anionic sodium dodecylsulfate(SDS)and neutral TX-100 surfactantas the other component.Fluorescence quenching and laser photolysis studies indicate that thefunctional surfactants are solubilized at different sites in micelles,the process depends on chainlength and exerts great influence on the quenching of zinc phthalocyanine excited states.     

Study of Spontaneous Imbibition of Water by Oil-Wet Sandstone Cores Using Different Surfactants

The mechanism of spontaneous imbibition of water by sandstone cores and the relationship between reservoir wettability and imbibition recovery were studied by investigating factors influencing the spontaneous imbibition of different surfactants by oil-wet sandstone cores. Ultimate oil recovery of cores using the cationic surfactant CTAB was higher than that of the cores using the nonionic surfactant TX-100 and the anionic surfactant POE (1) at the same concentration. For CTAB and TX-100, the ultimate oil recovery by spontaneous imbibition increased with increase in surfactant concentration. In regard to imbibition recovery, TX-100 and POE(1) at high temperatures were superior to those at low temperatures. Ultimate oil recovery of the high-permeability core was higher than that of the low-permeability core at room temperature. According to changes in the driving force during the imbibition process, the imbibition curve could be divided into three regions: (1) mainly capillary force, (2) both capillary and gravity forces, and (3) mainly gravity force. The stronger the hydrophilicity of the rock surface, the higher the spontaneous imbibition recovery.     

SURFACTANT MEDIATED POLYMERIZATION KINETICS OF ACRYLAMIDE USING CR(VI)-CYCLOHEXANONE REDOX SYSTEM

The effect of organized surfactants on the kinetics of acrylamide (AM) polymerization have been studied over a temperature range of 25–45°C using Cr (VI)-cyclohexanone (CH) redox system as initiator. The rate of polymerization, R_p(obs), as well as, the percentage of the monomer conversio were found to be increased with increasing the concentration of the anionic surfactant (SDS), above its CMC. But the cationic surfactant (CTAB) reduced the rate considerably at higher concentration, while non-ionic surfactant (TX-100) played no role on the rate. The effect of [Cr(VI)], [CH], [AM], [H+], and ionic strength on the rates have also been examined. The presence of 0.015M SDS decreased the overall activation energy of the polymerization by 6.28 k.Cal/ mole as compared to that in the absence of a surfactant. On increasing the SDS concentration, the viscosity average molecular weight was also found to increase. For the polymerization process, a mutable mechanistic scheme has been pro-posed.     

A novel approach for the preparation of AgBr nanoparticles from their bulk solid precursor using CTAB microemulsions

Microemulsions are suitable reaction media to prepare a wide variety of nanoparticles and provide control over their sizes. However, as typically used, microemulsions limit rates of rapid reactions and suffer from low reactant solubilization capacity. This work presents a new application of a novel approach aimed at minimizing these limitations. This approach, which was previously applied for AgCl nanoparticle preparation, involves solubilization of a bulk silver halide in the form of higher halides, by means of reaction with the surfactant counterion of a microemulsion, and the reprecipitation of silver halide nanoparticles in the water pools of individual reverse micelles. CTAB microemulsions were employed because they possess a reactive counterion and are known to have a high solubilization capacity for ionic reactants. Despite their high solubilization capacity, CTAB microemulsions achieved lower nanoparticles uptake (molar concentration of the colloidal nanoparticles) for the same surfactant concentration when compared to our previous study. The effect of the following variables on the nanoparticle uptake and the particle size was investigated: (1) operation variables, including rate of mixing and temperature; and (2) microemulsion variables, including CTAB and n-butanol concentrations, and water-to-surfactant mole ratio, R. These variables provide a comprehensive test to the proposed mechanism and expose the role of the surfactant layer rigidity. The nanoparticle uptake increased as the rate of mixing, temperature, and CTAB concentration increased, and decreased as n-butanol concentration and R increased. High n-butanol concentration and R values reduced the effective surfactant concentration and contributed to less surfactant layer rigidity and to particle aggregation.     

Submicellar catalytic effect of cetyltrimethylammonium bromide in the oxidation of ethylenediaminetetraacetic acid by MnO4-

The effects of cetyltrimethylammonium bromide (CTAB), sodiumdodecyl sulphate (SDS) and Triton X-100 (TX-100) on the oxidative degradation of ethylenediaminetetraacetic acid (EDTA) by MnO₄⁻ have been studied spectrophotometrically at 525 and 420 nm, respectively. It was found that cationic surfactant catalyse the reaction rate while anionic and non-ionic have no effect. The premicellar environment of CTAB strongly catalyses the reaction rate which may be due to the favorable electrostatic binding of both reactants (MnO₄⁻ and EDTA) with the positive head groups of the CTAB aggregates. The influence of different parameters such as [MnO₄⁻], [EDTA], [H⁺] and [surfactants] were also considered. The reaction follows the first- and fractional-order kinetics with respect to [MnO₄⁻] and [EDTA]. The proposed mechanism and the derived rate law are consistent with the observed kinetics.     

Role of surfactants in clouding phenomenon of imipramine hydrochloride

The clouding behavior of tricyclic antidepressant drug imipramine hydrochloride (IMP) in aqueous solution has been studied in presence of surfactants. A pH increase in the presence as well as in the absence of surfactants decreased the CP. Drug molecules become neutral at high pH and therefore head–head repulsion decreases which lead to CP decrease. Addition of non-ionic and cationic surfactants increased the CP whereas anionic surfactants showed a peaked profile. Effect of CTAB/TX-100 at different fixed drug concentrations showed that at all surfactant concentrations the CP value was higher for higher drug concentrations. However, variation of pH produced opposite effect: CP at all CTAB/TX-100 concentrations decreased with increasing pH. All results are interpreted in terms of increase in hydrophobicity or hydrophilicity of micelles on addition of surfactants.     

Influence of Nonionic Surfactant on Alkaline Hydrolysis of Methyl Violet Catalyzed by Cetyltrimethylammonium Bromide

The alkaline hydrolysis of methyl violet (MV) was studied by spectrophotometric method under pseudo-first-order conditions at 298 K. Cationic surfactant cetyltrimethylammonium bromide (CTAB) catalyzed the reaction. Addition of nonionic surfactant Triton X-100 (TX-100) exhibited significant influence on the CTAB catalyzed reaction by lowering the extent of catalysis. The kinetic data were analyzed by Piszkiewicz model of positive cooperativity. Linear Hill-type plots were generated with indices of cooperativity values greater than unity. The effect of counterions on the reaction rates was also studied in the presence of cationic surfactant (CTAB) and cationic–nonionic mixed surfactants (CTAB/TX-100).     

Synthesis of ZnO nanoparticles in 2-propanol by reaction with water

We report on the synthesis of ZnO particles from Zn(CH(3)CO(2))(2) in 2-propanol as a function of the concentration of water, in the absence of a base such as NaOH. Particles with diameters of 3-5 nm are formed depending on time, temperature, and water concentration. The nucleation and growth are slower than in the presence of NaOH, and at longer times the increase in particle size is dominated by diffusion-limited coarsening. The rate constant for coarsening increases with increasing water concentration up to 150 mM, above which the rate constant is 1.1 x 10(-4) cm(3) s(-1), independent of the water concentration. The width of the particle size distribution decreases with increasing water concentration, and at 250 mM water, the full width at half-maximum of the distribution function is essentially the same as for the synthesis of ZnO using NaOH as a reactant. The temperature dependence of coarsening is determined by the bulk solubility of the ZnO nanoparticles and yields an apparent activation energy of 1.12 eV. This is significantly larger than the activation energy of 0.35 eV for coarsening of ZnO from 1 mM Zn(CH(3)CO(2))(2) in 2-propanol with 1.6 mM NaOH.     

Interaction of poly(vinylpyrrolidone) with cationic and nonionic surfactants in aqueous solution studied by <Superscript>1</Superscript>H NMR

Aqueous solutions of surfactant at various concentrations with 0.2% poly(vinylpyrrolidone) (PVP) were studied by ¹H NMR methods, including relaxation time and self-diffusion coefficient measurements and two-dimensional nuclear Overhauser enhancement spectroscopy. Two surfactants were concerned: cationic cetyltrimethylammonium bromide (CTAB) and nonionic Triton X-100 (TX-100). In the presence of 0.2% PVP, the variation of the T ₂ values of CTAB protons is similar to that in the absence of PVP. Relaxation times of PVP protons are not significantly affected by the increasing concentration of CTAB. This indicates that no interaction between PVP and CTAB could be detected. However, in the presence of 0.2% PVP, TX-100 micelles are formed at a concentration lower than its normal critical micellization concentration. According to the results of relaxation time measurement of water protons, the presence of 0.2% PVP also induces the contraction of the hydrophilic layer of the TX-100 micelle. This indicates some interaction between PVP and TX-100, but the mechanism of this interaction needs further investigation.     

吲哚方酸菁染料在表面活性剂水溶液中的光降解

考察了4种含有不同N位取代基的对称吲哚方酸菁染料在阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)、阴离子表面活性剂十二烷基硫酸钠(SDS)和非离子表面活性剂曲拉通(TX-100)水溶液中的光降解行为,结果表明,表面活性剂对染料分子具有保护作用,其影响大小为CTAB>TX-100>SDS,分子中有羧基的染料受影响程度最大。在表面活性剂浓度较低时,染料光降解程度随着表面活性剂浓度的增加而增加,但形成胶束后,染料的光降解程度则随着表面活性剂浓度的升高而降低。     

Influence of surfactants on the adsorption and elektrokinetic properties of the system: guar gum/manganese dioxide

The adsorption of non-ionic polysaccharide—guar gum (GG) in the presence or absence of the surfactants: anionic SDS, cationic CTAB, nonionic TX-100 and their equimolar mixtures SDS/TX-100, CTAB/TX-100 from the electrolyte solutions (NaCl, CaCl₂) on the manganese dioxide surface (MnO₂) was studied. The increase of GG adsorption amount in the presence of surfactants was observed in every measured system. This increase results from formation of complexes between the GG and the surfactant molecules. This observation was confirmed by the determination of the influence of GG on surfactants adsorption on the MnO₂ surface. The increase of GG adsorption on MnO₂ was the largest in the presence of the surfactant mixtures (CTAB/TX-100; SDS/TX-100) which is the evidence of the synergetic effect. The smallest amounts of adsorption were obtained in the presence of TX-100, which results from non-ionic character of this surface active agent. In the case of single surfactant solution CTAB has the best efficiency in increasing the amount of GG adsorption on MnO₂ which results from strong interactions with GG and also with the negatively charged surface of the adsorbent. In order to determine the electrokinetic properties of the system, the surface charge density of MnO₂ and the zeta potential measurements were performed in the presence of the GG macromolecules and the above mentioned surfactants and their mixtures. The obtained data showed that the adsorption of GG or GG/surfactants complexes on the manganese dioxide surface strongly influences the diffused part of the electrical double layer (EDL)—MnO₂/electrolyte solution, but has no influence on the compact part of the electric double layer. This is the evidence that the polymers chains are directly bonded with the surface of the solid and the surfactants molecules are present in the upper part of the EDL.     

Polarographic behavior of nicotinamide in surfactant media and its determination in cetyltrimethylammonium bromide surfactant system

The behavior of nicotinamide has been studied by differential pulse polarography and cyclic voltammetry in the presence of certain ionic and nonionic surfactants, viz. cetyltrimethylammonium bromide (CTAB), sodium dodecylsulfate (SDS) and Triton X-100 (TX-100). The cathodic peak potential (E(p(c))) and peak current (I(p(c))) of nicotinamide were found to be remarkably dependent on the charge and concentration of the surfactant. The presence of SDS and that of TX-100 cause a shift in peak potential and a change in peak current of nicotinamide. In the presence of the cationic surfactant, CTAB, an enhancement in the sensitivity of nicotinamide was observed. A sharp peak with more than two-fold increase in current was used to determine the limit of detection and linear working range using the differential pulse polarographic technique. The present method was successfully used for the simultaneous determination of nicotinamide and pyridoxine hydrochloride, and for the determination of nicotinamide in multivitamin pharmaceutical preparations.     

Hydrophobic terminal group of surfactant initiating micellization as revealed by 1H NMR spectroscopy

The critical aggregation concentration (CAC) of four with three kinds of conventional surfactants, namely, two cationic surfactants [hexadecyltrimethyl ammonium bromide (CTAB) and tetradecyltrimethyl ammonium bromide (TTAB)], one anionic surfactant [sodium dodecyl sulfate (SDS)], and a nonionic surfactant [Triton X-100 (TX-100)], were determined by variation of ¹H chemical shifts with surfactant concentrations. Results show that the CAC values of protons at different positions of the same molecule are different, and those of the terminal methyl protons are the lowest, respectively, which suggests that the terminal groups of the alkyl chains aggregates first during micellization. Measurement of the transverse relaxation time (T₂) of different protons in SDS also show that the terminal methyl protons start to decrease with the increase in concentration first, which supports the above mentioned tendency.     

Optimization of dye-doped silica nanoparticles prepared using a reverse microemulsion method

Fluorescent labeling based on silica nanoparticles facilitates unique applications in bioanalysis and bioseparation. Dye-doped silica nanoparticles have significant advantages over single-dye labeling in signal amplification, photostability and surface modification for various biological applications. We have studied the formation of tris(2,2'-bipyridyl)dichlororuthenium(II) (Ru(bpy)) dye-doped silica nanoparticles by ammonia-catalyzed hydrolysis of tetraethyl orthosilicate (TEOS) in water-in-oil microemulsion. The fluorescence spectra, particle size, and size distribution of Ru(bpy) dye-doped silica nanoparticles were examined as a function of reactant concentrations (TEOS and ammonium hydroxide), nature of surfactant molecules, and molar ratios of water to surfactant (R) and cosurfactant to surfactant (p). The particle size and fluorescence spectra were dependent upon the type of microemulsion system chosen. The particle size was found to decrease with an increase in concentration of ammonium hydroxide and increase in water to surfactant molar ratio (R) and cosurfactant to surfactant molar ratio (p). This optimization study of the preparation of dye-doped silica nanoparticles provides a fundamental knowledge of the synthesis and optical properties of Ru(bpy) dye-doped silica nanoparticles. With this information, these nanoparticles can be easily manipulated, with regard to particle size and size distribution, and bioconjugated as needed for bioanalysis and bioseparation applications.     

Controlling oriented aggregation using increasing reagent concentrations and trihalo acetic acid surfactants

Zinc oxide particle growth from homogenous solutions prepared with isopropyl alcohol was monitored using in situ UV–vis spectroscopy, and results show that the rate of ZnO particle growth and the final ZnO nanoparticle size depend strongly upon the concentrations of precursors and the identity of surfactants used. In addition, particle size versus time data was fit using the coarsening model and the simultaneous oriented aggregation and coarsening model in order to evaluate the effect of changing synthetic variables on the mechanism of nanoparticle growth. In general, an increase in growth by oriented aggregation with increasing precursor concentrations was observed, a result that was consistent with results from high-resolution transmission electron microscopy (HRTEM) characterization. The increase in precursor concentrations resulted in an increase in the number concentration of ZnO nanoparticles, which resulted in a higher probability of particle–particle interactions and hence increased growth by oriented aggregation. Additionally, particle growth in solutions of trifluoro-, trichloro-, and tribromoacetate surfactants was studied, and growth by oriented aggregation followed the trend expected based on the number concentration of zinc oxide particles. Growth with trifluoroacetate was an exception, with growth by oriented aggregation substantially suppressed.     

Shape tunable synthesis of anisotropic gold nanostructures through binary surfactant mixtures

In recent years, much effort has been made to produce gold (Au) nanorods of different sizes through the use of binary surfactant mixtures via a seed-mediated growth approach. However, how the ratio of two different surfactants influences the shape of the resulting Au nanoparticles remains to be elucidated. Here, we report the shape-controlled synthesis of Au nanoparticles using a binary surfactant mixture of CTAB (cetyltrimethylammonium bromide) and DDAB (didodecyldimethylammonium bromide) via a silver-assisted seed-mediated growth approach. Decreasing the CTAB/DDAB ratio results in a shape transition from Au nanorods to elongated tetrahexahedra and finally to Au bipyramids. The results showed significant improvement in the yield of Au bipyramidal type nanoparticles in different sizes (nm to μm) by using binary surfactant mixtures without any need for shape selection procedure. By varying the pH and concentration of ascorbic acid, we can control the shape and size of Au nanoparticles (i.e., truncated bipyramids, dogbones, and nanodumbbells) at fixed CTAB/DDAB ratios. A preliminary growth mechanism has been proposed based on the change in the mixed micelle soft-template induced by the increasing concentration of DDAB and reaction parameters (i.e., pH, concentration of ascorbic acid). These results constitute the advances in the understanding for synthesizing anisotropic Au nanoparticles of tunable optical properties via engineering the design of a soft-template. These anisotropic Au nanoparticles, especially, bipyramids of different morphologies and sizes are potential candidates for the enhancement of the optical response and developing label-free biosensing devices.     

Synergistic effect of mixed anionic and cationic surfactant systems on the interfacial tension of crude oil-water and enhanced oil recovery

Surfactant based enhanced oil recovery (EOR) is an interesting area of research for several petroleum researchers. In the present work, individual and mixed systems of anionic and cationic surfactants consisting of sodium dodecyl sulphate (SDS) and cetyltrimethylammonium bromide (CTAB) in different molar ratios were tested for their synergistic effect on the crude oil-water interfacial tension (IFT) and enhanced oil recovery performance. The combination of these two surfactant systems showed a higher surface activity as compared to individual surfactants. The effect of mixed surfactant systems on the IFT and critical micellar concentration (CMC) is strongly depends on molar ratios of the two surfactant. Much lower CMC values were observed in case of mixed surfactant systems prepared at different molar ratios as compared to individual surfactant systems. The lowest CMC value was found when the molar concentration of SDS was higher than the CTAB. When the individual and mixed surfacant systems were tested for EOR performance through flooding experiments, higher ultimate oil recovery was obtained from mixed surfactant flooding compared to individual surfactants. Combination of SDS and CTAB or probably other anionic-cationic surfactants show synergism with substantial ability to reduce crude oil water IFT and can be a promising EOR method.