Enthalpies of dilution from 50 to 225°C of aqueous decyltrimethylammonium bromide

Enthalpies of dilution of aqueous decyltrimethylammonium bromide have been measured from 0.56 to about .005 mol-kg^–1 and from 50 to 225°C near the saturation pressure of water using a flow calorimeter. The changes of the stoichiometric osmotic and activity coefficients with temperature, the excess apparent molar heat capacity, and the apparent and partial relative molar enthalpies have been calculated from the data.     

Volumes,heat capacities and solubilities of amyl compounds in decyltrimethylammonium bromide aqueous solutions

Apparent molar heat capacities and volumes of amylamine (PentNH₂) 0.02m, capronitrile (PentCN) 0.02m and nitropentane (PentNO₂) 0.009m in decyltrimethylammonium bromide (DeTAB) micellar solutions, in water and in octane were measured at 25°C. By assuming that their concentration approaches the standard infinite dilution state, heat capacities and volumes were rationalized by means of previously reported equations following which the distribution constant between the aqueous and the micellar phase and heat capacity and volume of the additives in both phases are simultaneously derived. The present results are compared to those we have previously obtained for pentanol (PentOH). The thermodynamic properties of PentNH₂ in water and in micellar phase are substantially identical to those of PentOH but different from those of PentCN and PentNO₂ whereas the opposite behavior was observed in their pure liquid state and in octane. The nature of the solvent medium seems to affect the thermodynamic behavior of PentNH₂. Also, the study of the apparent molar heat capacities of the amyl compounds investigated here in micellar solutions as a function of surfactant concentration shows evidence of a maximum at about 0.4m DeTAB, which can be attributed to a micellar structural transition. Accordingly, the solubilities of PentCN and PentNO₂ as a function of the DeTAB concentration drop in the neighborhood of the concentration where heat capacities display the maximum.     

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.     

Computational study of the structure and behavior of aqueous mixed system sodium unsaturated carboxylate-dodecyltrimethylammonium bromide

The mixed surfactant system sodium 10-undecenoate (SUD)-dodecyltrimethylammonium bromide (DTAB) was studied by computational simulation to determine the composition and structure of the mixed microstructures. Results were contrasted with experimental data obtained from literature and our own laboratory. The modelization predicts spherical or cylindrical micelles with a preferential composition of SUD-DTAB of about 1:2, while the system predicts a lamellar structure with a proportion of 1:1 when SUD is replaced by the saturated soap sodium undecanoate. The model also predicts the deep inclusion of bromide ions in the micelle Stern layer. All predictions were in agreement with previous experimental results.     

Observation of micelle solution of decyltrimethylammonium bromide by electrospray ionization mass spectrometry

A micelle solution of decyltrimethylammonium bromide (DTAB) was analyzed by electrospray ionization mass spectrometry. Finding an appropriate range of a capillary-skimmer potential was a prerequisite for obtaining a satisfactory spectrum. The mean molecular weight of DTAB aggregates, 10,500, was deduced from a series of mass spectra acquired at different capillary-skimmer potentials. The value was comparable with the micelle weight, previously determined by the light-scattering method.     

Surface and volume properties of dodecylethyldimethylammonium bromide and benzyldimethyldodecylammonium bromide: II. Volumetric properties of dodecylethyldimethylammonium bromide and benzyldimethyldodecylammonium bromide

Density measurements were carried out for aqueous solutions of two cationic surfactants: dodecylethyldimethylammonium bromide (C₁₂(EDMAB)) and benzyldimethyldodecylammonium bromide (BDDAB). On the basis of the obtained results of the measurements the CMC and partial molar volumes of the surfactants studied were also determined. The obtained CMC values were also analyzed with those accounted on the basis of the surface tension data from the previous paper [J. Harkot, B. Jańczuk, J. Colloid Interface Sci. (2008), submitted for publication]. The values of CMC determined from the surface tension and density measurements for C₁₂(EDMAB) are equal to 9.9×10⁻³ and 1.5×10⁻² M and for BDDAB to 5.25×10⁻³ and 5.3×10⁻³ M, respectively. These obtained values are very similar. However, in the literature it is difficult to find the CMC values for C₁₂(EDMAB) and BDDAB determined by these two methods used by us—especially from the density measurements for BDDAB and surface tension measurements for C₁₂(EDMAB). In the case of the apparent molar volumes of C₁₂(EDMAB) there is a good agreement between the values obtained by us and those found in the literature. The CMC values for C₁₂(EDMAB) and BDDAB were also determined on the basis of their surface tension and free energy of electrostatic interactions between the polar heads of these surfactants and compared with those obtained from the surface tension and density measurements. It was found that the theoretically obtained CMC values were close to those determined from the density and surface tension data for the C₁₂(EDMAB) and that the ratios of the CMC values of the surfactants to their concentration at which the water surface tension decreased by about 20 mN/m proved that the presence of the aryl group in the BDDAB head instead of the methyl group caused that its micellization process was more inhibited in relation to its adsorption at air–water interface than that of C₁₂(EDMAB).     

碳氟表面活性剂与碳氢表面活性剂混合水溶液的表面吸附和胶团形成 I: 全氟辛酸钠-溴化辛基三甲铵体系

The surface adsorption and micelle formation of the mixed aqueous solutions of sodium perfluorooctanoate (7CFNa) and n-octyltrimethylamonium bromide (C8NBr) have been investigated by studying the surface tension-concentration relations of the solutions. It has been found that (1) The surface activity of the mixed system is much higher than that of 7CFNa and C8NBr. C8NBr is a very effective synergist for 7CFNa in surface activity, and vice versa. (2) By applying Gibbs adsorption equation, the total amount of adsorption (\I\t), the individual adsorption amount of the single surfactants (\I\7CF-, \I\C8N+) and the average molecular areas of them have been calculated. The adsorption value (saturated, \I\T) increases by 54% as the molal ratio of 7CFNa-C8NBr varies from 100:1 to 1:300. (3) From the adsorption data, it appears that the structure of surface layer of the 7CFNa-C8NBr solutions is peculiar and quite different from that of the cationic-anionic hydrocarbon surfactants. Firstly, the molal ratio of the two components in the surface layer of the 1:1 mixed solution is not 1:1 (7CFNa is adsorbed perferentially). Secondly, the molecular area at the maximum adsorption is very small (22.7A2). This could be attributed to the balancing of the electrical attraction between positive and negative ions and the mutual phobicity between the fluorocarbon and hydrocarbon chains. It has been concluded that the saturated adsorption film would possibly have a double-layer structure: the upper layer consists of the oriented 7CF- with the fluorocarbon chain toward the gaseous phase and the lower layer consists of randomly oriented C8N+ with the positive ionic head attached to the negative ionic head of 7CF- -- thus the 7CF- adsorption layer would behave as a platform for the adsorption of C8N+. (4) The limiting surface tension of the mixed solutions is very low (-15mNm-1) even if the molal ratio of 7CFNa-C8NBr is small, and so is the oil-water interfacial tension. Therefore it is capable of spreading the dilute aqu     

Surface charge properties of Fe2O3 in aqueous and alcoholic mixed solvents

Iron oxide (Fe2O3) was identified and characterized by surface area, X-ray diffractometry, and FTIR analyses. Surface charge densities, point of zero charge (PZC), and surface ionization constants were determined from the potentiometric titration data in various aqueous and aqueous organic mixed solvents in the temperature range 293-313 K. The surface charge densities were observed to decrease with the increase in temperature and concentration of metal ions in both the aqueous and aqueous organic mixed solvents. The absolute values of the surface charge density were found to change in the order aqueous > aqueous/methanol > aqueous/ethanol. Further, the PZC of the iron oxide was observed to shift to the higher pH values in the order ethanol > methanol > aqueous solution, which indicated a decrease in the acidity of the surface -OH groups. The pKa1 and pKa2 values of iron oxide were also determined and then used for determination of the surface potential (psi0) of the solid in aqueous and aqueous organic mixed solvents. The surface potential-surface charge curves generally supplemented the results derived from psi0-pH curves.     

Surface and bulk properties of aqueous binary mixtures of Pluronic F68 and low-molecular-weight cationic surfactants: 2. Wetting and modifying effects of mixed solutions

Wetting and adsorption modification of polystyrene surface with aqueous solutions of F68-cationic surfactant mixtures are studied. The synergism of wetting is revealed. It is established that the degree of synergism upon wetting is determined by the synergism of surfactant adsorption on a solid surface and peculiarities of the formation of mixed adsorption layers of surfactants. It is shown that low-molecular-weight cationic surfactants can be used to increase the efficiency of the modification of polymer surfaces with Pluronics.     

Structure and physico‐chemical properties in mixed aqueous solution of sodium alkylcarboxylate‐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 cationc‐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.     

Surface and bulk properties of aqueous binary mixtures of Pluronic F68 and low-molecular-weight cationic surfactants: 1. Surface tension and association in aqueous solutions

Surface tension of aqueous binary mixtures of Pluronic F68 and low-molecular-weight cationic surfactants is measured. The synergistic a decrease in surface tension is revealed. It is shown that this effect is controlled by the chemical structure of cationic surfactants and determined by an increased (compared to the bulk) content of Pluronic F68 in the surface layer, which is formed due to the adsorption of the individual molecules of mixture components.     

Transport properties of alkyltrimethylammonium bromide surfactants in aqueous solutions

Differential mutual diffusion coefficients of n-alkyltrimethylammonium bromides [CH₃(CH₂)_n–1N(CH₃)₃Br, C_nTAB] (n=10, 12, 14, 16) have been measured in aqueous solutions at 298.15 K using a conductimetric cell and an automatic apparatus to follow diffusion. The cell is based on an open-ended capillary, and the technique follows the diffusion process by measuring the resistance of a solution inside the capillaries at various times. The electrical conductances of those solutions have also been measured to calculate the critical micellar concentration (cmc). Thermodynamic analysis of the data suggests that the free ion concentration decreases at concentrations above the cmc, in agreement with theoretical predictions. The obtained values of the micellization parameters were used to model the mutual diffusion coefficients of C_nTAB aqueous solutions.     

Surface and bulk properties of severely fluorinated carbon fibres

The development of ultra-inert composites using fluorinated carbon fibres as the reinforcement requires fluorinated carbon fibres with a durable surface composition. Here we report the effect of direct fluorination using an F₂/N₂ mixture at 653 K on the surface and bulk properties of two types of high strength carbon fibres. These were treated up to a surface fluorine content of ∼64 at.% and a bulk fluorine content of ∼15 mass%. A colour change was observed after fluorination caused by the changes in the graphitic band structure of the carbon fibres by the introduction of carbon sp³ hybridisation. The tensile strength and Young's modulus decrease after fluorination by up to 33 and 22%, respectively. XRD shows marginal changes in the interlayer distance but the crystallite size increases. Changes in the electrical conductivity of the fluorinated carbon fibres indicate that the modification is confined to the near surface volume. Predominantly covalent C-F bonds are formed as shown by X-ray photoelectron spectroscopy (XPS) and measured zeta (ζ)-potentials. Hence the fluorinated fibres are hydrophobic and have low surface tensions. This and the large increase in fibre surface area, as determined by nitrogen adsorption, is expected to facilitate interfacial interaction between fluorinated carbon fibres and fluoropolymers.     

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。     

Surface structure and properties of mixed fumed oxides

A variety of fumed oxides such as silica, alumina, titania, silica/alumina (SA), silica/titania (ST), and alumina/silica/titania (AST) were characterized. These oxides have different specific surface areas and different primary particle composition in the bulk and at the surface. These materials were studied by FTIR, NMR, Auger electron spectroscopy, one-pass temperature-programmed desorption with mass spectrometry control (OP TPDMS), microcalorimetry, and nitrogen adsorption. Nonlinear changes in the surface content of alumina in SA and AST and titania in ST and AST samples with increasing oxide content along with simultaneous changes in their specific surface area cause complex dependencies of the heat of immersion in water and desorption of water on heating on the structural parameters. Simultaneous analysis of changes in the surface phase composition, in the concentration of hydroxyls, and in the structural characteristics reveals that at a low content of the second phase the structural characteristics (e.g., S(BET)) are predominant; however, at a large content of these oxides the phase composition plays a more important role.     

Photoactivity of nanostructured TiO2 catalysts in aqueous system and their surface acid-base, bulk and textural properties

This work reports on the characterisation and determintion of the photocatalytic activity of some TiO₂ catalysts prepared using TiCl₄ as precursor. The samples, consisting of suspensions, dispersions or powders of nanonstructured anatase or rutile phases, were obtained in very mild conditions, i.e., by boiling the solution obtained after hydrolysis of TiCl₄ at atmospheric pressure: it is worth noting that no calcination was necessary to obtain photoactive phases. The samples were characterised by X-ray diffraction (XRD), determination of the BET specific surface area (SSA), scanning electron microscopy (SEM) observations and diffuse reflectance spectroscopy (DRS). FT-IR spectroscopy was used to study the surface acidity of the solids. Photodegradation of 4-nitrophenol and gemfibrozil (5-(2,5-dimethylphenoxy)-2,2-dimethyl-pentanoic acid) was used as probe reactions to evaluate the photoactivity and the obtained results showed that the home prepared samples are effective to degrade both substrates. The photoreactivity results were compared to those obtained using commercial photocatalysts.     

The ethidium bromide dimer. Absorption and fluorescence properties in aqueous solutions

Absorption and fluorescence spectral changes of ethidium bromide in aqueous solutions of increasing concentration have been interpreted in terms of dimer formation. The dimerization constant and the dimer absorption properties have been found to depend on the ionic strength of the solution. The dimer is non-fluorescent. A further process of dimer formation has been hypothesized in the excited state to give account of the whole self-quenching effect measured. A dimer geometry has been proposed to interpret the dependence of the photophysical properties of the ethidium cation complexed with double strand DNA on the extent of binding.     

The aqueous catanionic system sodium perfluorooctanoate-dodecyltrimethylammonium bromide at low concentration

The interaction between sodium perfluorooctanoate (SPFO) and dodecyltrimethylammonium bromide (DTAB) was studied by several methods and it was found strongly synergistic. Above a mole fraction of SPFO in the surfactant mixture (alpha(SPFO))=0.38, the interaction is repulsive and increases with the content of SPFO in both, the overall mixture and micelles, whereas the interaction is attractive if DTAB is in excess. At alpha(SPFO)=0.38 the low miscibility between hydrocarbon and fluorocarbon is counterbalanced by the electrostatic attraction between the opposite charged head groups, and the micelle composition is ideal (i.e., the mole fraction of SPFO in micelles X(SPFO)=alpha(SPFO)=0.38). The solubility of fluorocarbon in hydrocarbon is lower than that of hydrocarbon in fluorocarbon. Micelles of DTAB act as a solvent for SPFO without important structural changes, whilst micelles of SPFO undergo important changes when dissolve DTAB. This asymmetry may be interpreted as caused by the difference in chain length that favors the inclusion of the shorter chain in micelles of the longer surfactant, but disfavors the opposite process. Above X(SPFO)=0.5 there is an excess adsorption of bromide ions on the mixed micelles surface, giving rise to a high zeta potential. Micelles of pure SPFO or pure DTAB show an important energy barrier which prevents micelle flocculation. The inclusion of SPFO in DTAB micelles produces a reduction of the energy barrier, which disappeared when alpha(SPFO)=0.5. This produces the flocculation of micelles giving rise to the formation of a non-birefringent coacervate, which is probably formed by unordered isometric clusters of micelles.     

The aqueous cationic system sodium undecenoate-dodecyltrimethylammonium bromide at low concentration

The aqueous sodium undecenoate (SUD) –dodecyltrimethylammonium bromide (DTAB) catanionic system was studied at low concentration. The system did not precipitate, even at a 1:1 SUD:DTAB proportion, but showed the formation of a coacervate in a range of surfactant mixture compositions. Micelles have a preferential composition of 0.37 mole fraction of SUD. This behavior is attributed to the presence of the double bond at the distal extreme of the SUD molecule, which can form hydrogen bonds with water. Consequently, the –CH=CH₂ group is situated at the interface between the hydrocarbon micelle core and water, reducing the interfacial free energy. Structural computations demonstrate that the mentioned SUD proportion produces complete coverage of the micelle surface by the double bonds.