Aqueous Solutions Of Hexadecyltrimethylammonium Bromide Research Articles

Foaming in aqueous solutions of hexadecyltrimethylammonium bromide and silica nanoparticles: Measurement and analysis of rheological and interfacial properties

ABSTRACTThe properties of aqueous foams stabilized by a mixture of negatively charged silica nanoparticles and hexadecyltrimethylammonium bromide were studied in this work. Rheological properties of the foams were studied. The interaction between nanoparticles and surfactant molecules in the bulk phase was studied by zeta potential and size measurements of the particles. The interaction at the interface was studied by means of interfacial shear rheology, surface pressure measurement, and atomic force microscopy. It was found that foams were more stable at low surfactant concentrations, though the foamability was low. This was due to the formation of a strong viscoelastic film of surfactant-laden particles at the air–water interface. A suitable mechanism has been proposed to explain the stability of foams in the presence of nanoparticles at different surfactant concentrations.

Calculation aspects of diffusion coefficients in micellar solutions of ionic surfactants

Results of calculating diffusion coefficients of ionic surfactants as functions of their concentration in micellar solutions have been analyzed within the framework of the quasi-chemical variant of the law of mass action. Diffusion coefficients have been evaluated for an ideal mixture of monomeric molecules and micelles, as well as taking into account the correction for the variability of the aggregation number of a surfactant using aqueous solutions of hexadecyltrimethylammonium bromide, hexadecylpyridinium chloride and bromide, and alkyltriphenylphosphonium bromides as examples.

X-ray Reflectivity Measurements for Freezing Transitions of Alkane Wetting Film on Surfactant Solution Surface

Abstract X-ray reflectivity measurements were applied to hexadecane wetting film on aqueous solutions of hexadecyltrimethylammonium bromide (CTAB) and tetradecyltrimethylammonium bromide (TTAB). In both cases, the monolayers in which oil molecules are penetrated from hexadecane droplets into surfactant-adsorbed films were found at room temperature. Upon cooling, they showed first-order freezing transitions, however, it was also confirmed that the structures of freezing films were qualitatively different: hexadecane molecules were frozen together with CTAB to form mixed solid monolayer in CTAB–hexadecane while the frozen hexadecane monolayer wetted mixed liquid monolayer in TTAB–hexadecane.

Thermodynamic Properties of CTAB in Aqueous Solutions of Neutral Polymers at 25°C

Interactions of polyethylene glycols (PEGs) and polypropylene glycols (PPOs) in aqueous solutions of hexadecyltrimethylammonium bromide (CTAB) were investigated through thermodynamic properties at 25°C. The densities and heat capacities of the solutions were measured with a vibrating tube densimeter and a Picker flow microcalorimeter, respectively. The variations in the apparent molar volumes and heat capacities of both solutes, calculated from the densities and heat capacities of the solutions, are unusually large in the vicinity of the CMC, reflecting the existence of very strong interactions between CTAB and PPOs. With the more hydrophilic polymers, PEGs, the apparent properties of CTAB are less affected by the presence of the polymer, indicating that PEGs interact only weakly with CTAB.

Effect of Solubilization of Aliphatic Hydrocarbons on Size and Shape of Rodlike C16TABr Micelles Studied by 2H NMR Relaxation

Multifield 2H relaxation has been used to quantify the effect of solubilization of alkanes on the size and shape of the micelles in aqueous solutions of hexadecyltrimethylammonium bromide, C16TABr. Information about aggregate size and shape was deduced from the reorientation rate of the aggregates. The surfactant concentration was chosen so that the solutions without solubilizate contained moderately long rodlike micelles (axial ratio ∼4). It was found that the change in aggregation behavior upon solubilization is substantially different for solubilizates of similar chemical composition but different structures. Solubilization of small amounts of cyclohexane, cyclooctane, cyclodecane, trans-decalin, n-hexane, 2,3-dimethylbutane, or adamantane causes growth of the micelles. Further addition of these solubilizates (except for adamantane, which has a lower solubility limit than the other solubilizates) causes a decrease in the aggregate size. On the other hand, solubilization of n-octane, n-decane, or n-dode...

Measurement of Dynamic Interfacial Properties in an Overflowing Cylinder by Ellipsometry

Ellipsometry has been used to analyze the surface of aqueous solutions of hexadecyltrimethylammonium bromide in an overflowing cylinder. The factors affecting the precision and accuracy of the ellipsometric measurements are discussed and ellipsometry is compared with surface tensiometry as a method for studying dynamic interfacial properties. The coefficient of ellipticity was found to vary quadratically with radial distance from the center of the cylinder, in agreement with models proposed in earlier literature. The dynamic surface tension inferred from noninvasive ellipsometric measurements is much higher than previously reported measurements of the dynamic surface tension obtained with a Wilhelmy cylinder.

Study of the 2,6-o-Dimethyl-β-cyclodextrin + Hexadecyltrimethylammonium Bromide + Water System from Speed of Sound Measurements

The effect of the presence of 2,6-o-dimethyl-β-cyclodextrin (DIMEB) on aqueous solutions of hexadecyltrimethylammonium bromide (CTAB), due to the formation of inclusion complexes, has been analyzed by measuring the speed of sound, u, in two complementary studies: (1) as a function of [CTAB] in the presence of different constant concentrations of DIMEB, and (II) as a function of [DIMEB] for various nonmicellar and micellar solutions of CTAB. Two kinds of inclusion complexes between DIMEB and CTAB have been detected: a 1:1 complex (DIMEB:CTAB) in excess of CTAB with respect to DIMEB, and a 2:1 complex (DIMEB2:CTAB) in excess of DIMEB with respect to CTAB, not usually found in this type of system. On the other band, the presence of the cyclodextrin causes the apparent critical micellar concentration, CMC*, to increase upon the addition of cyclodextrin, while the concentration of free surfactant available for the micellization process in the postmicellar region, [CTAB]r, remains basically constant.

Shape transitions in the aqueous phase of the system hexadecyltrimethylammonium bromide—hexanol—water

Viscosity, conductivity, density, and ultrasonic velocity measurements have been used to characterize aqueous solutions of hexadecyltrimethylammonium bromide and hexanol, i.e., the L 1 phase of the system. At surfactant molalities below 0.055 m, conductivity and ultrasonic velocity measurements show that a change in the solubilization pattern takes place as hexanol is added. It seems that above a certain hexanol content, the additive is solubilized not only in the palisade layer but also in the interior of the micelles, thus producing swollen micelles. The viscosity remains practically constant as hexanol is added. At surfactant molalities above 0.055 m the relative viscosity increases drastically above a certain hexanol content and the conductivities show a maximum at this point. This suggests a shape transition from spherical to larger rod- or disklike micelles. At surfactant molalities between 0.055 and 0.09 m hexadecyltrimethylammonium bromide, the viscosities start to decrease at even higher hexanol contents. The conductivity and ultrasonic velocity measurements also show that a change in solubilization pattern takes place at this hexanol content. It seems likely that hexanol becomes solubilized in the micellar interior and that a breakdown from large aggregates to spherical swollen micelles takes place. It seems that the L 1 phase of the system hexadecyltrimethylammonium bromide—hexanol—water can be divided into four structurally different regions; one of monomeric species, one of ordinary spherical micelles, one of swollen spherical micelles, and one of rod- or disklike micelles.

Intrinsic basicity constant of 10-phenyl-10-(hydroxyimino)decanoate in aqueous solutions of hexadecyltrimethylammonium bromide. Effect of salts and detergent concentration

Influence de la concentration en bromure de trimethylhexadecylammonium et de l'ajout de NaBr, NaCl et NaF sur l'equilibre de protonation du groupement hydroxyimino, en solution aqueuse basique a 30°C

Solubilization of 1-hexanol in hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, and sodium decanoate

The solubility of hexanol has been measured in aqueous solutions of hexadecyltrimethylammonium bromide (HTAB), sodium dodecyl sulfate (NaDDS), and sodium decanoate (NaC 10). In the HTAB and NaDDS solutions the hexanol solubility decreased abruptly above a surfactant content of about 0.05 mole kg −1, suggesting a structural change from spherical to anisodiametric micelles. The total solubility of hexanol shows that it must be solubilized both in the palisade layer and in the micellar interior of these spherical micelles. After the structural change has taken place less hexanol is solubilized so that all can be accomodated in the palisade layer. No decrease in solubility has been observed for the NaC 10 system, and the total hexanol solubility is so small that all can be accommodated in the palisade at all NaC 10 concentrations. Δ H o and Δ S o of solubilization for spherical micelles have been calculated from the temperature dependence of the distribution coefficient.

ESR linewidth broadening of a hydrophobic probe in some surfactant solutions

ESR linewidth of tetradecanoyloxy-2,2,6,6-tetramethyl-piperidinyl-l-oxyl was observed in aqueous solutions of hexadecyltrimethylammonium bromide and sodium alkyl (C12 and C14) sulfates at 30 °C. The linewidth increases quadratically with the spin probe concentration to various extents, depending upon micellar properties. The diversity of the linewidth broadening is, however, reduced by plotting the relative linewidth, W/W0, vs. the average solubilization number, m, where W0 is the linewidth at the extremely dilute spin probe concentration. All the experimental points fall on a curve regardless of the diverse micellar properties. The broadening is interpreted in terms of a bimolecular and multimolecular collisions between the spin probes exclusively concentrated in micelles in accordance with the Poisson distribution of the spin probe.

An Ultrasonic Study of Sphere to Rod Transitions in Aqueous Solutions of Hexadecyltrimethylammonium Bromide.

An Ultrasonic Study of Sphere to Rod Transitions in Aqueous Solutions of Hexadecyltrimethylammonium Bromide.

Formation of Micelles of Hexadecyltrimethylammonium Bromide in Water-N,N-Dimethylformamide Solutions

Abstract The critical micellar concentration of aqueous solutions of hexadecyltrimethylammonium bromide (HTAB) containing various amounts of N,N-dimethylformamide (DMF) has been determined at 25 and 40 °C by means of surface tensiometric measurements. The standard free energy (ΔGm°), enthalpy (ΔHm°) and entropy (ΔSm°) of micellization were also determined. The experimental results indicate that: (1) micelle formation is somewhat hindered by a raise in temperature, and (2) DMF has an inhibitory effect on the formation of micelles of HTAB. This effect is relatively small at low DMF concentrations, but it increases drastically as the mole fraction of DMF approaches 0.33. The changes in the ΔGm°, ΔHm°, and ΔSm° values indicate that the formation of HTAB micelles in the water-DMF mixtures is an entropy directed process at lower concentrations of DMF and the inhibitory effect of DMF on micelle formation is attributed to an increase in the orderliness of this system with increasing DMF concentration.

Concentration and temperature dependence of the counterion self-diffusion coefficient in aqueous solutions of hexadecyltrimethylammonium bromide

The concentration and temperature dependence of the counterion self-diffusion coefficient, D Br − , have been measured for aqueous solutions of hexadecyltrimethylammonium bromide (cetyltrimethylammonium bromide, CTAB), from below the critical micelle concentration (CMC = 0.036 wt%) to 17.3 wt% CTAB. The radiometric-porous frit method was used. The concentration dependence of D Br − and of the activation energy for self-diffusion both apparently exhibit extrema near the CMC. However, above about 1% CTAB D Br − is a linear function of the concentration, and this concentration dependence continues even at high surfactant concentrations where the viscosity of the solution becomes very large. The data are analyzed in terms of a “two-site” model which has been applied to the NMR linewidths of Br − in CTAB solutions, and it is shown that within the model the accepted interpretation of the linewidths is inconsistent with the bromide self-diffusion coefficient.

1H, 13C, 35Cl, and 81Br NMR of aqueous hexadecyltrimethylammonium salt solutions: Solubilization, viscoelasticity, and counterion specificity

A combination of 1H, 13C, 35Cl, and 81Br NMR is used to investigate counterion specificity and solubilization behavior of hexaldecyltrimethylammonium micelles. The concentration dependence of the quadrupole relaxation of 81Br − and 35Cl − counterions in aqueous solutions of hexadecyltrimethylammonium bromide (CTAB) and chloride (CTAC), respectively, is found to be quite different and this can be referred to the formation of large elongated micelles in the former case but not in the latter. This striking difference is maintained in solutions containing both CTAB and CTAC. This is attributed to the coexistence of two types of micelles and a considerable specificity in the counterion binding, the Br − ions having a preference for the cylindrical and the Cl − ions for the globular micelles. For mixtures of CTAB with tetradecyltrimethylammonium chloride (TTAC), the same type of counterion specificity in 35Cl and 81Br NMR was observed as for mixtures of CTAB and CTAC. The 13C chemical shifts are closely the same for solutions of either CTAB, CTAC, or TTAC, but in mixtures of CTAB + TTAC or CTAC + TTAC there is a marked splitting of the ω-CH 3 resonance into two peaks. This is referred to alkyl chain packing disturbances in mixed micelles of two amphiphiles with different alkyl chain lengths. 1H and 13C NMR were employed to study the solubilization site for viscoelastic solutions of CTAB and 1-methylnaphthalene. A highly variable effect along the amphiphile chain was observed for both 1H and 13C relaxation and shielding. It could be established that solubilization of 1-methylnaphthalene occurs toward the polar part of CTAB micelles, about seven methylenes being affected appreciably. Chain flexibility is found to be influenced in a complex way by solubilization.

Solubilization of benzene and cyclohexane in aqueous solutions of hexadecyltrimethylammonium bromide: a deuterium magnetic resonance study

Quadrupole splittings in the 2H NMR spectrum from C 6D 6 and C 6D 12 solubilized in aqueous solutions of hexadecyltrimethylammonium bromide (CTAB) have been observed in the hexagonal liquid crystalline phase (E) as well as in the concentrated micellar phase (L 1). The order parameter that is obtained for solubilized C 6D 6 is more than two orders of magnitude greater than previously reported from measurements of linear dichroism spectra. Various possibilities for the nature of the solubilization sites are discussed.