Comparison of the coadsorption of benzyl alcohol and phenyl ethanol with the cationic surfactant, hexadecyl trimethyl ammonium bromide, at the air-water interface

A comparison of the coadsorption of benzyl alcohol and phenyl ethanol with the cationic surfactant, hexadecyl trimethyl ammonium bromide, C16TAB, at the air-water interface is made using the specular reflection of neutrons. The phenyl ethanol is more surface active than the benzyl alcohol, and competes more effectively with the C16TAB for the interface. The structure of the C16TAB component in the mixed monolayer is compared with the structure of the pure C16TAB monolayer at an equivalent area per molecule. The addition of the aromatic alcohol subtly alters the conformation of the C16TAB and draws it closer to the aqueous subphase. The center of the alcohol distribution is located in the interface adjacent to the C6 group of the C16TAB alkyl chain closest to the headgroup. Compared to the benzyl alcohol, the more hydrophobic phenyl ethanol is slightly farther away from the headgroup, and has a greater impact on the conformation of the alkyl chain of the C16TAB.     

Efficiently removing cetyl trimethyl ammonium bromide from wastewater by graphene oxide

Cetyl trimethyl ammonium bromide (CTAB) containing wastewater from dressing plant may pose a detrimental threaten to mineral beneficiation and environment. The adsorption of CTAB in aqueous solutions by graphene oxide (GO) has been studied in this work. X-ray diffraction, X-ray photoelectron spectroscopy, Fourier-transform infrared spectrometer, and atomic force spectroscopy were used to characterize GO. The results indicated that the adsorption followed the Freundlich model could be well described by pseudo-second order kinetic model. The adsorption capacity was much bigger than activated carbon and many natural clay minerals. The adsorption process was endothermic, and the adsorption mechanism of CTAB onto GO was proven to be controlled by surface complexation, hydrogen bonding, and electrostatic attraction.     

Thermoanalytical investigations on hydrous zirconia

The variations in the thermoanalytical curves for three differently produced powders of hydrous zirconia are discussed in connection with X-ray measurements and powdermetallurgical characterization. They were shown to characterize the ZrO₂-H₂O bonding and the thermal treatment for the calcination of hydrous zirconia. They allowed selection of the product with the most favourable microstructure for a high sinter activity, an explanation of the phase formation and phase transformations, and estimations of the energy content of the amorphous material and the thermal stability of the tetragonal phase. It was shown that thermal analysis is an appropriate method for the optimizing of ZrO₂-powder production.

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Zusammenfassung Die Unterschiede der thermoanalytischen Effekte für drei verschieden hergestellte wasserhaltige ZrO₂-Pulver wurden in Verbindung mit Röntgenuntersuchungen und der pulvermetallurgischen Charakterisierung diskutiert. Es zeigte sich, daß man mit ihrer Hilfe die ZrO₂-H₂O-Bindung und die thermische Behandlung bei der Kalzinierung des wasserhaltigen ZrO₂ formulieren kann. Sie erlauben, das Produkt mit der günstigsten Mikrostruktur für eine hohe Sinteraktivität auszuwählen, die Phasenbildung un Phasenumwandlungen zu erklären, den Energieinhalt des amorphen Materials und die thermische Stabilität der tetragonalen Phase abzuschätzen. Es erwies sich, daß die Thermoanalyse eine geeignete Methode zur Optimierung der ZrO₂-Pulver-Herstellung ist.

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Interaction between biosurfactant surfactin and cationic surfactant cetyl trimethyl ammonium bromide in mixed micelle

An anionic/cationic mixed surfactant aqueous system of surfactin and cetyl trimethyl ammonium bromide (CTAB) at different molar ratios was studied by surface tension and fluorescence methods (pH 8.0). Various parameters that included critical micelle concentration (cmc), micellar composition (X ₁), and interaction parameter (β ^m) as well as thermodynamic properties of mixed micelles were determined. The β ^m was found to be negative and the mixed system was found to have much lower cmc than pure surfactant systems. There exits synergism between anionic surfactin and cationic CTAB surfactants. The degree of participation of surfactin in the formation of mixed micelle changes with mixing ratio of the two surfactants. The results of aggregation number, fluorescence anisotropy, and viscosity indicate that more packed and larger aggregates were formed from mixed surfactants than unmixed, and the mixed system may be able to form vesicle spontaneously at high molar fraction of surfactin.     

Fluorescence enhancement effect for the determination of DNA with calcein-cetyl trimethyl ammonium bromide system

A new spectrofluorimetric method was developed for the determination of trace amounts of DNA using the calcein as a fluorescent probe. In the presence of appropriate amounts of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB), the anionic dye calcein dimerizes. The weak fluorescence intensity of the dimer was enhanced by adding DNA at pH 6–7. The interaction between calcein–CTAB and DNA was studied on the basis of this behavior and a new method was developed for determining DNA. Under the optimal conditions, the enhanced fluorescence intensity was in proportion to the concentration of DNA in the range of 4.0 × 10⁻⁶ to 8.0 × 10⁻⁵ g L⁻¹ for fsDNA and thermally denatured ctDNA (4.5 × 10⁻⁶ to 9.0 × 10⁻⁵ g L⁻¹). The detection limits (S/N = 3) were 2.0 × 10⁻⁶ and 2.2 × 10⁻⁶ g L⁻¹, respectively. This method was used for determining the concentration of DNA in synthetic samples with satisfactory results.     

Study on dynamic interfacial tension of 3-dodecyloxy-2-hydroxypropyl trimethyl ammonium bromide at liquid/liquid interface

Dynamic interfacial tension between aqueous solutions of 3-dodecyloxy-2-hydroxypropyl trimethyl ammonium bromide (R₁₂HTAB) and n-hexane were measured using the spinning drop method. The effects of the R₁₂HTAB concentration (the concentration below the CMC) and temperature on the dynamic interfacial tension have been investigated; the reason of the change of dynamic interfacial tension with time has been discussed. The effective diffusion coefficient, D_a, and the adsorption barrier, _a, have been obtained from the experimental data using the extended Word–Tordai equation. The results show that the dynamic interfacial tension becomes smaller while _a becomes higher with increasing R₁₂HTAB concentration in the bulk aqueous phase. D_a decreases from 5.56 × 10⁻¹² m⁻² s⁻¹ to 0.87 × 10⁻¹² m⁻² s⁻¹ while _a increases from 5.41 kJ mol⁻¹ to 7.74 kJ mol⁻¹ with the increase of concentration in the bulk solution of R₁₂HTAB from 0.5 × 10⁻³ mol dm⁻³ to 4 × 10⁻³ mol dm⁻³. Change of temperature affects the adsorption rate through altering D_a and _a. The value of D_a increases from 5.56 × 10⁻¹² m⁻² s⁻¹ to 13.98 × 10⁻¹² m⁻² s⁻¹ while that of _a decreases from 5.41 kJ mol⁻¹ to 5.07 kJ mol⁻¹ with temperature ascending from 303 K to 323 K. The adsorption of surfactant from the bulk phase into the interface follows a mixed diffusion–activation mechanism, which has been discussed in the light of interaction between surfactant molecules, diffusion and thermo-motion of molecules.     

Thermodynamics of anion exchange on hydrous zirconia: IV. Calorimetric determination of the heat of anion exchange on hydrous zirconia

Ion-exchange processes Cl^?/NO^?₃ and SO^2?₄/NO^?₃ were studied by calorimetric measurements. Experiments were so performed to obtain stoichiometric equilibrium concentration in order to calculate equilibrium constants, and the heat studied ion-exchange reaction. As a result ?11.03 and ?21.70 kJ mol^?1 values were obtained for standard enthalpy changes of Cl^?/NO^?₃ and SO^2?₄/NO^?₃ ion exchange processes, respectively.These values, together with these obtained from distribution measurements were used for calculation of free energy and standard entropy changes of investigated processes.     

Study of beta-cyclodextrin/fluorinated trimethyl ammonium bromide surfactant inclusion complex by fluorinated surfactant ion selective electrode

The construction and performance of a liquid membrane electrode responsive to N-(1,1,2,2-tetrahydroperfluorooctyl)-N,N,N-trimethylammonium bromide (FTABr) and its use for the study of β-cyclodextrin/fluorinated surfactant inclusion complex is described. The electrode is based on the use of tetrahydroperfluorooctyltrimethylammonium-tetraphenylborate ion pair as electro active material in polyvinyl chloride (PVC) matrix plasticized using 2-Nitrophenyl octyl ether (NPOE). The electrode exhibits a fast, stable, reproducible and “Nernstian” response (59 ± 2 mV) for FTABr over the concentration range of 10⁻⁵ to 2 × 10⁻³ mol L⁻¹ at 298 K. The lowest detection limit is 2 × 10⁻⁶ mol L⁻¹ and the response time is around 20-30 s. The validity of the electrode, for detection of fluorinated surfactant ions and hence to carry out electrochemical measurements to study micellization of fluorinated surfactant, is verified by comparing the critical micelle concentration (cmc) value of FTABr obtained by using the electrode, with that obtained by surface tension measurements. Association constant K for β-cyclodextrin/FTABr complex is evaluated from the potentiometric measurements carried out using this electrode and is observed to be ∼1.26 × 10⁵. The results suggest that β-cyclodextrin forms an equimolar association complex with the FTA⁺ surfactant ion.     

十二烷基硫酸钠与溴化正辛基三甲基铵混合表面活性剂水溶液的表面吸附及胶团形成

本文研究了盐存在时不同比例的十二烷基硫酸钠(简称12CH)和溴化正辛基三甲基铵(简称C8NBr)混合物的表面活性、表面吸附以及胶团形成等性质,结果表明:(1)正、负离子表面活性剂混合物具有很高的表面活性,不论其混合比例如何,临界胶团浓度(cmc)及cmc时溶液的表面张力(γcmc)皆较任何单一组分时小;(2)不论体相中比例如何,表面层中12CH和C8NBr的饱和吸附量的摩尔比皆～1.7且总饱和吸附量亦皆～5.2x10[-10]mol.cm[-2].由此求得表面层中分子截面积为32A[2],与由分子结构计算的数据相近,说明正、负表面活性离子排列紧密;(3)与碳链长相同的正、负离子型表面活性剂混合水溶液比较,本体系反应离子浓度对cmc有明显影响,证实表面层带电,胶团也带电;(4)计算了离子强度相同,温度不同时和温度相同、离子强度不同时的热力学量,得出离子强度大者易形成胶团。     

Kinetic study on the reaction of lauric acid with ethanol catalyzed by deep eutectic solvent based on cetyl trimethyl ammonium bromide

In this work, a novel type of deep eutectic solvents (DES: CTAB–DES) based on cetyl trimethyl ammonium bromide (CTAB) was successfully synthesized by mixing CTAB with p-toluenesulfonic acid monohydrate and applied as catalysts for the esterification reaction of ethanol and lauric acid. The kinetics of the reaction of ethanol and lauric acid catalyzed by CTAB–DES was investigated in the temperature range of 328.15–348.15 K. The influence of different parameters including agitation speed, temperature, catalyst loading, and the lauric acid to ethanol molar ratio on the conversion of lauric acid was discussed. The kinetic experimental data obtained were correlated by the pseudo-homogeneous model, and the results show that it can predict the reaction process well. Moreover, CTAB–DES can be reused six times without any significant decrease in catalytic activity.     

Proton conduction in indium hydrogensulfate and hydrous zirconia composites

Solid composite proton electrolytes based on indium hydrogensulfate and hydrous zirconia are studied. A composite effect is observed in these systems: their proton conductivity is higher than in the starting components. Maximal conductivities are achieved at a comparatively low concentration of hydrous zirconia (10% wt %) in composites heat-treated at 373 K. The increasing surface basicity of hydrous zirconia as a result changing its deposition pH noticeably improves the low-temperature conductivity of the composites. Irreversible processes that decrease the conductivity occur in composites even during treatment at temperatures above 373 K. A third component (neutral indium sulfate) only decreases the conductivity.     

The effects of ammonium sulfate and sulfamic acid on the surface acidity of sulfated zirconia

In this work, sulfated zirconia (SZ) was prepared by a solvent-free method, ammonium sulfate ((NH₄)₂SO₄) and sulfamic acid (NH₂SO₃H) were as sulfur sources, respectively. The resulting catalysts were characterized by powder X-ray diffraction (XRD), thermogravimetric analysis and differential scanning calorimetry (TGA-DSC), N₂ adsorption–desorption isotherms, inductively coupled plasma (ICP) and pyridine-FTIR. The characterization of the catalysts revealed that SZ prepared with (NH₄)₂SO₄ as sulfur source contained more Lewis acid sites and less Brønsted acid sites. The effects of sulfur sources on the catalytic activity of catalysts were studied. Catalytic testing showed that SZ prepared with (NH₄)₂SO₄ as sulfur source had a better catalytic performance for removing trace olefins from aromatics.     

Superoxide radical anions on the surface of zirconia and sulfated zirconia: formation mechanisms, properties and structure

In situ ESR spectroscopy has been used for direct comparison of different thermal and light-induced processes leading to generation of superoxide radical anions on the surface of various zirconia and sulfated zirconia materials. For materials of both types the magnetic resonance parameters of the radical anions were found to be practically independent of the generation method, except for oxygen coadsorption with NO that yields radicals with somewhat smaller gz values. The parameters appear to depend mostly on the state of the surface zirconia cations stabilizing the radical anions, so that the g tensor anisotropy is significantly smaller over sulfated zirconia. It is shown that light-induced formation of superoxide radical anions in the presence of coadsorbed hydrocarbons can be initiated with visible light. Original SIET reaction mechanisms are suggested for the formation of superoxide radical anions by coadsorption with hydrocarbons and illumination after such coadsorption to extend the previously known ones to account for the observed phenomena. Cluster model DFT calculations of magnetic resonance parameters of O2- radical anions stabilized on the surface of zirconium dioxide showed that the adsorption complexes have a -shape rather than linear structure. The magnetic resonance parameters obtained by calculations practically match experimental data and adequately describe their changes after the surface modification with sulfates.     

Ion transport in MF-4SK membranes modified with hydrous zirconia

Composites based on perfluorinated cation-exchange membranes MF-4SK with embedded hydrous zirconia were synthesized. The composites have higher proton conductivity, lower diffusion permeability, and higher ion-transport selectivity than unmodified MF-4SK membranes. Diffusion permeability anisotropy was found in samples with heterogeneous dopant distribution across the membrane.     

Pressure effects on lipidic direct phases: the dodecyl trimethyl ammonium chloride-water system

The direct lyotropic polymorphism of dodecyltrimethylammonium chloride (DTAC) was investigated by synchrotron X-ray diffraction at different water concentrations under compression up to 2 kbar, i.e., in the pressure intermediate range where interesting biophysical transformations occur and the functional characteristics of cell membranes are altered. The results show that pressure induces the transition from the hexagonal phase to the micellar Pm3n cubic phase in hydrated samples (c between 0.5 and 0.6, c being the weight concentration of lipid in the mixture) and the transition from the bicontinuous Ia3d cubic phase to the hexagonal phase in drier samples (c = 0.8). By increasing the pressure on very dry samples, a lamellar L(alpha) phase was observed to form transitorily at the Ia3d cubic-hexagonal phase transition. Phase compressibility and then the lipid and water partial molecular compressibilities were derived as a function of pressure and concentration. As a result, we assessed the very low compressibility of the hydration water within the lipid phases, and we demonstrated that the compressibility of DTAC is very dependent on pressure. Moreover, the molecular parameters of DTAC calculated in the different phases during compression confirmed that pressure induces small but continuous conformational changes, definitely different from the large changes observed in lipid molecules forming type II structures.     

Micellization of dodecyldimethylethyl- ammonium bromide in aqueous solution

Specific conductivity of aqueous solutions of dodecyldimethylethylammonium bromide has been determined in the temperature range of 15-40°C. The critical micelle concentration (cmc) and ionization degree of the micelles, b, were determined from the data. Thermodynamic functions, such as standard Gibbs free energy, ΔG _m°, enthalpy, ΔG _m°, and entropy, ΔG _m°, of micellization, were estimated by assuming that the system conforms to the mass action model. The change in heat capacity upon micellization, ΔG _m°, was estimated from the temperature dependence of ΔG _m°. An enthalpy-entropy compensation phenomenom for the studied system has been found. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis, characterization, and catalytic activity of phosphomolybdic acid supported on hydrous zirconia

A series of ecofriendly solid acid catalyst was synthesized by phosphomolybdic acid impregnated on hydrous zirconia (ZPMA) by an incipient wetness impregnation technique. The support and the resulting catalysts were characterized by X-ray diffraction, FTIR, EPMA, BET surface area, acid sites, etc. These studies indicate that the phosphomolybdic acid keeps its Keggin-type structure unaltered up to 500 degrees C. Catalytic activities of the material were evaluated for the esterification of acetic acid reaction. The 12 wt% of phosphomolybdic acid supported on hydrous zirconia shows highest surface area, acid sites and gives about 86% conversion with 100% selectivity of n-butyl acetate.     

Micelle formation in sodium hexadecyl sulfate surfactant solutions studied by small-angle neutron scattering

Micelle formation in aqueous sodium hexadecyl sulfate solutions is studied by small-angle neutron scattering. Measurements are carried out at different concentrations (1.1, 2.2, 3.2, 5.4, 10.9 and 32.8 mM/dm³) and at different temperatures (40°, 50°, and 60°C). The monotonous evolution of interparticle correlation can be observed on the measured scattering patterns. At high concentrations (10.9 and 32.8 mM/dm³) scattering patterns are described by interacting ellipsoids, but at low concentrations by non-interacting ellipsoids. Computation of the distance distribution function proved the ellipsoidal shape at 10.9 and 32.8 mM/dm³, but showed an unexpectedly large particle dimension and elongation of the micelles at lower concentrations.