Dodecyltrimethylammonium Bromide Micelles Research Articles

Hydrogen bonding. Part 41.1 Factors that influence the distribution of solutes between water and hexadecylpyridinium chloride micelles

M. H. Abraham, H. S. Chadha, J. P. Dixon, C. Rafols and C. Treiner, J. Chem. Soc., Perkin Trans. 2, 1997, 19 DOI: 10.1039/A604722J

Spherical dodecyltrimethylammonium bromide micelles in the limit region of transition to rod-like micelles. A light scattering study

Dynamic and static light scattering measurements were performed on dodecyltrimethylammonium bromide aqueous solutions in the presence of sodium bromide at different concentrations. The power law dependence was applied to the diffusion coefficient D vs. c b ( c, surfactant concentration) and the decrease of the parameter b with increasing salt concentration was observed. The dependencies of D and b on the salt concentration are decreasing and show a plateau at intermediate salt concentrations. The Debye plot from the static light scattering measurements shows the presence of stable spherical micelles in the solution at low salt concentration with molecular weight about 23 000 and aggregation number 65–80. The logarithmic plot of the molecular weight vs. the ionic strength shows two linear regions with an intercept at the salt concentration 1.9 M. However, the values of the molecular weight and the aggregation number are too small to allow the assumption of a rod structure.

Fluorescence Analysis of Single and Mixed Micelle Systems of SDS and DTAB

Structural features of the single and mixed micellar systems of sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) were characterized using the fluorescence probe 6-propionyl-2-(dimethylamino)naphthalene (Prodan). In particular, our investigations capitalized on the spectral sensitivity of Prodan to its environment as well as the extensive solubility of Prodan in solvents of varying polarity and/or hydrophobicity to effectively use a three-mode factor analysis technique to resolve the coincident emission from Prodan in multiple microenvironments of single and mixed micelle systems. Our investigations reveal parameters of Prodan fluorescence that reflect the relative polarities of the surfaces of SDS and DTAB micellar cores, the permeability of the SDS micelle interface, and the heterogeneity of SDS−DTAB mixed micellar systems. In particular, we observe a strong affinity of Prodan for both SDS and DTAB micelles at the water−surfactant interface with the emission λmax of Prodan consistent with greater water accessibility in the SDS interfacial region. Reduction in SDS head-group repulsion upon the addition of both an alkali metal series of counterions (Li+ → Na+ → K+) and a tetrasubstituted ammonium series of counterions (NH4+ → N(CH3)4+ → N(CH3CH2)4+ → N(CH3CH2CH2CH2)4+) appears to induce a more nonpolar environment for Prodan. Each one-phase and two-phase region of the dilute aqueous binary SDS−DTAB pseudoternary diagram is identified by distinct Prodan λmax values. Evidence is presented for the presence of SDS−DTAB mixed micelle systems.

Effect of Crown Ether 1,4,7,10,13,16-Hexaoxacyclooctadecane on the Structure of Sodium Dodecyl Sulfate and Dodecyltrimethylammonium Bromide Aqueous Micellar Solutions

The effects of the addition of crown ether 1,4,7,10,13,16-hexaoxacyclooctadecane on the structure of aqueous solutions of surfactants sodium dodecyl sulfate and dodecyltrimethylammonium bromide have been studied by small angle neutron scattering. By modeling the scattering intensities, it was possible to derive, simultaneously, both structural properties and information on the distribution of crown ether between the micellar and aqueous phases. In the case of sodium dodecyl sulfate, an appreciable amount of crown ether was found to be localized in the micellar phase, though it was not possible to establish whether it was in the core or in the shell ; there was no evidence of crown ether localization in dodecyltrimethylammonium bromide micelles. The above observations indicate that although, at least in principle, the crown ether methylene groups could interact hydrophobically in the micellar core with the surfactant alkyl chains, the ability of crown ethers to form metal complexes might also lead, in sodium dodecyl sulfate solutions, to electrostatic interactions in the external palisade between the crown ether-sodium ion complex and the surfactant head groups. The absence of crown ether from dodecyltrimethylammonium bromide micelles indicates that the macrocyclic molecules interact with sodium dodecyl sulfate micelles via the formation of a complex between the sodium ion and the crown ether and rules out the possibility of hydrophobic interaction in the micellar core.

Mixed Micelles of Dodecyltrimethylammonium Bromide and Didodecyldimethylammonium Bromide

Mixed micelles of dodecyltrimethylammonium bromide (DTAB) and didodecyldimethylammonium bromide (DDAB) are investigated with small-angle neutron scattering (SANS). The roughly spherical DTAB micelle elongates, and the fraction of condensed bromide ions increases, as the DDAB-DTAB mixing ratio increases at a constant total surfactant concentration. The aggregate composition matches that predicted by an ideal mixing model. SANS contrast variation experiments using partially deuterated DTAB (DdTAB) confirm the modeling parameters determined from fully hydrogenated surfactant samples and provide consistent structural information about the interfacial region.

Micellar effects on reaction kinetics: Part II. Study of the action of dodecyltrimethylammonium bromide on the reactions between Pyrogallol Red and chromium(VI), vanadium(V) and titanium(IV)

The complexation kinetics and equilibrium of the reactions of vanadium(V) and titanium(IV) with Pyrogaliol Red (PGR), and the kinetics of oxidation of chromium(VI) by PGR were studied in micellar solutions of dodecyltrimethylammonium bromide (DTAB). The 1:1 PGR-V(V) and 2:1 PGR-Ti(IV) complexes formed in an aqueous medium associate with DTAB molecules of the micellar system to yield the new complexes 1:1:2 PGR-V(WDTAB and 2:1:1 PGR-Ti(IV)-DTAB. The stability constants of the ternary complexes were calculated by considering the volume fraction of micelles and were compared with those determined from the overall solution volume. The binding constants for the associates of PGR, chromium(VI), vanadium(V), titanium(IV), PGR-V(V) and PGR-Ti(IV) complexes with DTAB micelles were spectrophotometrtcally determined. The observed rate of formation of the PGR-Ti(IV) complex was increased by the presence of DTAB micelles, but the second-order rate constant in the micellar pseudo-phase was slightly lower than in water. Therefore, the whole rate increase observed was due to the concentration of reactants in the micellar pseudo-phase. The kinetics of formation of the PGR-V(V) complex could not be investigated by using the stopped-flow technique because the reaction was too fast in both the aqueous and the micellar medium. The second-order rate constant for the oxidation reaction between PGR and Cr(VI) was found to exceed that in aqueous solutions by a factor of ca. 55. Therefore, the increased rate observed for this reaction in the DTAB micellar medium can be ascribed to intrinsic effects of the micellar pseudo-phase on reactivity.

Multicomponent solubilization in aqueous micelles of dodecyl- and tetradecyltrimethylammonium bromide: Solubilization equilibria

Solubilization equilibria for hexane and a series of polycyclic aromatic compounds (dyes) in aqueous cationic micelles of dodecyltrimethylammonium bromide (DTAB) and tetradecyltrimethylammonium bromide (TTAB) were studied experimentally. Solubilizates were compared first individually, for effects of molecular shape and structure, and then as mixtures, in a search for interactive effects. Hexane solutions of solid dyes, in binary mixtures of relative mole fraction 0 to 1 for each dye, were partitioned into the aqueous micellar phase, which was analyzed by ultraviolet-visible spectrophotometry for the dyes and gas chromatography for hexane. Solubilization ratios (SRs), expressed as the ratio of solubilizate to surfactant molecules in a micelle, were obtained from the experimental data. In our experiments, the micelles contained more solubilized hexane than dye. For cases of three-component solubilization (two dyes and hexane), compounds of similar molecular shape and chemical structure performed alike as solubilizates, possibly occupying sites in the micelle interchangeably. However, when a large molecule with three or four fused rings and a smaller two-ring molecule were contained in the micelle, solubilization of the smaller molecule was always enhanced.

Some observations on the use of micellar media in the reaction between cerium(IV) and arsenic(III) catalysed by metal ions

The osmium(VIII)- and chromium(III)-catalysed cerium(IV)-arsenic(III) reaction was studied in the presence and absence of micelles of dodecyltrimethylammonium bromide (DTAB). The rate of the cerium(IV)-arsenic(III) reaction was increased by the presence of DTAB micelles, so the influence of the chemical catalyst on the micellar catalysis was studied. The kinetic studies undertaken show that both micelle- and ion-catalysed reactions occur in parallel and that the catalytic efficiency of each one determines the preferential route through which the reaction products are formed.

Effect of temperature on the salt-induced sphere–rod transition of micelles of dodecyltrimethylammonium bromide in aqueous NaBr solutions

The density of aqueous NaBr solutions of dodecyltrimethylammonium bromide (C12TAB) and ultrasound velocity in them have been measured as a function of surfactant concentration at NaBr concentrations 0–5.00 mol kg–1 and at temperatures 15–50 °C. Their adiabatic compressibility has been calculated by means of the Laplace equation. Based on a phenomenological treatment giving the density and the adiabatic compressibility of aqueous solutions of surfactant as a function of surfactant concentration, the apparent adiabatic compressibility of the surfactant in the form of spherical and rod-like micelles has been derived at different NaBr concentrations and at different temperatures.The apparent molar volume of the surfactant in the rod-like micelle is slightly larger than that in the spherical micelle at each temperature. The apparent adiabatic compressibility of the surfactant in the spherical micelle initially decreases upon addition of a small amount of NaBr, and then it remains constant or slightly increases with further addition of NaBr. The apparent adiabatic compressibility of the surfactant in the rod-like micelle increases with increasing NaBr concentration at each temperature, with an abrupt change at the threshold.The threshold NaBr concentration for the sphere–rod transition of the surfactant can be determined from variation of the apparent adiabatic compressibility of the surfactant in the micellar forms with NaBr concentration. It increases with rising temperature and changes from 1.64 mol kg–1 at 20 °C to 2.86 mol kg–1 at 45 °C.The initiation of the sphere–rod transition of micelles is attributed to a change in the hydration state of the surfactant with the NaBr concentration, and the threshold NaBr concentration is defined by the chemical potential of water in solution, with which hydration water on spherical and rod–like micelles are in equilibrium and where the hydration water has an equal escaping tendency on both micelles.

A study of competitive counterion binding to micelles using the acid-catalyzed reaction of hydrogen peroxide with iodide ions

The reaction involving the acid-catalyzed reduction of hydrogen peroxide by iodide ions has been used to study the competitive counterion binding of hydrogen ions to sodium dodecyl sulfate (SDS) micelles and iodide ions to both dodecyltrimethylammonium bromide (DTAB) and dodecyltrimethylammonium chloride (DTAC) micelles. It has been demonstrated that a pseudophase ion-exchange model can be employed to quantitatively describe, within certain limits, the competitive counterion binding in these ionic micellar systems. Ion-exchange constants have been determined for the hydrogen/sodium ion-exchange at the surface of SDS micelles, the iodide/bromide ion-exchange at the surface of DTAB micelles, and the iodide/chloride ion-exchange at the surface of DTAC micelles. These ion-exchange constants are 1.3 ± 0.4, 3.1 ± 0.3, and 8.2 ± 0.8, respectively.

The salt-induced sphere-rod transition of micelles of dodecyltrimethylammonium bromide in aqueous NaBr solutions as studied by the ultrasound velocity measurements

The density and adiabatic compressibility of aqueous NaBr solutions of dodecyltrimethylammonium bromide have been determined by means of pycnometry and ultrasound velocity measurements at 25°C. Phenomenological equations of density and adiabatic compressibility of micellar solutions have been given as functions of the concentration of the spherical micelle, to which the apparent molar volume and the apparent adiabatic compressibility are assigned. These equations have been further extended in such a way to be applicable for solutions containing both spherical and rod-like micelles, by introducing the apparent molar volume and the apparent adiabatic compressibility of a rod-like micelle. In the actual application of the present treatment, the concentration of the rod-like micelle has been obtained as a function of total micelle concentration by referring to the previous results of light scattering. Actually the density and adiabatic compressibility have changed linearly with total micelle concentration, even in the presence of both kinds of micelles. In this way the apparent molar volumes and the apparent adiabatic compressibilities of dodecyltrimethylammonium bromide in both spherical and rod-like micelles have been derived. Its apparent molar volume is slightly larger for the rod-like micelle than for the spherical one. Its apparent adiabatic compressibility is negative in the monomeric form, and its apparent adiabatic compressibility in spherical micelles changes in a somewhat complicated way with increasing NaBr concentration, while that in rod-like micelles increases less sharply with increasing NaBr concentration.

A comparative study of micellar solubilization for combinations of surfactants and solubilizates using the fourier transform pulsed-gradient spin—echo NMR multicomponent self—diffusion technique

The degree of solubilization for all combinations of 6 surfactants (sodium dodecanoate, sodium dodecyl sulfate, sodium octylbenzene sulfonate, sodium phenylundecanoate, dodecyltrimethylammonium bromide, and dodecylhexaethyleneglycolmonoether) and 12 solubilizates (1-pentanol, 2-pentanol, 3-pentanol, tert-pentanol, methyl-n-propyl ketone, diethyl ketone, benzene, benzyl alcohol, crown 18-6, crown 12-4, 1,4-dioxane, and ethyl glycol) have been determined at a surfactant concentration of 50 mg/ml D 2O solution and low total solubilizate/surfactant ratios. The most striking observations concern the solubilization behavior of the nonionic surfactant; with the aliphatic type it solubilizates weakly, with aromatics as strongly as the other surfactants, and with crown ethers hardly at all. With the exception that dodecyltrimethylammonium bromide micelles solubilize ketones more weakly in a relative sense, the remaining five surfactants exhibit very similar solubilization characteristics. NMR-based evidence with regard to the site of solubilization of aromatics is discussed.

The effect of fluorination on surfactant aggregation number and dye solubilization efficiency

Micellar aggregation numbers of 12,12,12-trifluorododecyltrimethylammonium bromide (TDTAB) and dodecyltrimethylammonium bromide (DTAB) were measured in several sodium bromide solutions by light scattering. At all sodium bromide concentrations from 0.1 to 1.5 m, DTAB micelles were found to be the larger. DTAB micelles were also found to have about twice the solubilizing power for the dye orange-OT as TDTAB micelles. Mutual phobicity between terminal CF 2 groups and hydrocarbon regions of surfactant ions and the dye provides a basis for understanding these observations.