Dodecyltrimethylammonium Bromide Molecules Research Articles

Salt Effect on the Complex Formation between Polyelectrolyte and Oppositely Charged Surfactant in Aqueous Solution

The complex formation between sodium carboxymethylcellulose (NaCMC) and dodecyltrimethylammonium bromide (DTAB) at various sodium bromide concentrations (C(NaBr)) has been studied by microcalorimetry, turbidimetric titration, steady-state fluorescence measurements, and the fluorescence polarization technique. The addition of salt is found to influence the formation of NaCMC/DTAB complexes markedly. At C(NaBr) = 0.00, 0.01, 0.02, 0.10, and 0.20 M, DTAB monomers form micelle-like aggregates on NaCMC chains to form NaCMC/DTAB complexes above the critical surfactant concentration (C1). At C(NaBr) = 0.23 M, DTAB molecules first form micelles above a 2.46 mM DTAB concentration prompted by the added salt, and then, above C1 = 4.40 mM, these micelles can aggregate with NaCMC chains to form NaCMC/DTAB complexes. However, at C(NaBr) = 0.25 M, there is no NaCMC/DTAB complex formation because of the complete salt screening of the electrostatic attraction between DTAB micelles and NaCMC chains. It is also surprisingly found that the addition of NaBr can bring out a decrease in C1 at C(NaBr) < 0.20 M. Moreover, the addition of NaBr to a mixture of 0.01 g/L NaCMC and 3.6 mM DTAB can directly induce the formation of NaCMC/DTAB complexes. This salt-enhancing effect on the complex formation is explained as the result of competition between the screening of interaction of polyelectrolyte with surfactant and the increasing of polyelectrolyte/surfactant interaction owing to the growth of micelles by added salt. When the increasing of polyelectrolyte/surfactant interaction exceeds the screening of interaction, the complex formation can be enhanced.

Novel phase behavior in adsorbed film of fluoroalkanol and cationic surfactant mixture

The surface tension of the aqueous solution of the binary mixture of 1H,1H-heptafluoro-1-butanol (FC4OH) and dodecyltrimethylammonium bromide (DTAB) was measured as a function of the total molality of the mixture and the composition (mole fraction in the surfactant mixture) of DTAB at 298.15 K under atmospheric pressure to examine the phase behavior in the adsorbed film. The results of the surface tension measurement were analyzed by the thermodynamic procedure proposed by us and the composition of the mixed adsorbed film in equilibrium with their bulk solution was calculated. Three different phases of the adsorbed film appeared by a subtle balance between the attractive interaction of the polar head groups and weak dispersion interaction of the hydrophobic chains. In the low-concentration regime, FC4OH molecules and DTAB molecules form a gaseous film and mix attractively in the whole composition by the long-range ion–dipole attraction between hydrophilic groups. The effect of the attractive dispersion interaction between C H and C F chains became more influential in the expanded film within a restricted composition region, where it should be noted that the interaction between C H and C F is weaker than that between C H chains or between C F chains alone. Furthermore, the adsorbed films at two specific compositions are stabilized by the stoichiometric arrangements of the molecules, which help ion–dipole attraction, in them.

Effect of molecular packing on adsorption and micelle formation of a homologous cationic surfactant mixture of hexadecyltrimethylammonium bromide and dodecyltrimethylammonium bromide

The surface tension of an aqueous solution of a hexadecyltrimethylammonium bromide (HTAB) and dodecyltrimethylammonium bromide (DTAB) mixture was measured as a function of the total molality and the composition of DTAB at 298.15 K under atmospheric pressure. The phase diagrams of adsorption and micelle formation were constructed and the excess Gibbs energy was evaluated by analyzing the phase diagrams thermodynamically. Both the excess Gibbs energy in the adsorbed film and the excess surface area are negative; therefore the mutual interaction between HTAB and DTAB is said to be stronger than that between the same species and is enhanced with increasing adsorption. By combining the results with those obtained in previous studies, we claimed that DTAB molecules can use effectively the space among the hydrocarbon chains of HTAB molecules and their polar head groups take a staggered arrangement at the surface so as to reduce the electrostatic repulsion. Consequently the dispersion force between hydrophobic chains becomes stronger. Furthermore, the comparison of the excess Gibbs energy in the adsorbed film with that in the micelle shows that the staggered arrangement of molecules is not necessary in the spherical micelle.

Coal Reverse Flotation. Part I. Adsorption of Dodecyltrimethyl Ammonium Bromide and Humic Acids onto Coal and Silica

Adsorption of dodecyltrimethyl ammonium bromide (DTAB) and humic acids (HA) on bituminous, oxidized bituminous, and subbituminous coals, as well as on silica, was studied through direct adsorption, electrokinetic, and contact angle measurements. It was concluded that the adsorption of DTAB and HA on a hydrophobic coal surface takes place through hydrophobic interactions between the hydrocarbon chains of these compounds and the hydrophobic coal surface. The adsorbed DTAB molecules cause a gradual decrease of coal hydrophobicity due to their tail-to-surface orientation. The adsorption density of DTAB on a hydrophilic/oxidized coal is much higher than on a bituminous coal. The results indicate that the adsorption mechanism involves some strong interactions between the cationic head group of the surfactant and the negatively charged oxygen groups on the coal surface. Despite the apparent head-to-surface orientation, the adsorbed DTAB molecules do not render the surfaces hydrophobic; this probably results from the fairly chaotic orientation of DTAB molecules on the surface of oxidized coal. The well-ordered conformation of the DTAB ions adsorbed onto the negatively charged silica surface, combined with significant adsorption of this surfactant at the solution/air interface makes the silica surface very hydrophobic.

Dodecyltrimethylammonium bromide-disodium dodecanephosphonate mixed micelles

The aqueous catanionic system dodecyltrimethylammonium bromide (DTAB)–disodiumdodecanephosphonate (DSDP) was studied by potentiometry, conductivity, surface tension, spectrometry and dye solubilization. No precipitation of neutral salts was found in the entire range of compositions studied. Up to four transitions were detected. The first transition, at about 0.001 mol dm−3, was probably related to a state change in the adsorption monolayer at the air/water interface. The second, at about 0.0065 mol dm−3, was probably related to the formation of ion pairs. The third transition was the critical micelle concentration which was analyzed with the pseudophase separation model and regular solution theory. The interaction between DTAB and DSDP molecules in micelles was weaker than in other cationic–anionic surfactant mixed micelles. Large, probably rodlike, micelles formed at the fourth transition at higher surfactant concentration. No vesicles or lamellar liquid crystals were detected. The adsorbed monolayer at the air/water interface was also studied by means of regular solution theory. It was much richer in DTAB than the micelles and the intermicellar solution. The interaction between DTAB and DSDP molecules at the air/water interface was very low. The results were explained on the basis of steric factors.

Energetic and binding properties of DNA upon interaction with dodecyl trimethylammonium bromide.

The interaction of dodecyl trimethylammonium bromide (DTAB), a cationic surfactant, with calf thymus DNA has been studied by various methods, including potentiometric technique using DTAB-selective plastic membrane electrode at 27 and 37 degreesC, isothermal titration microcalorimetry and UV spectrophotometry at 27 degreesC using 0.05 M Tris buffer and 0.01 M NaCl at pH 7.4. The free energy is calculated from binding isotherms on the basis of Wyman binding potential theory and the enthalpy of binding according to van't Hoff relation. The enthalpy of unfolding has been determined by subtraction of the enthalpy of binding from the microcalorimetric enthalpy. The results show that, after the interaction of first DTAB molecule to DNA (base molarity) through the electrostatic interaction, the second DTAB molecule also binds to DNA through electrostatic interaction. At this stage, the predom-inant DNA conformational change occurs. Afterwards up to 20 DTAB molecules, below the critical micelle concentration of DTAB, bind through hydrophobic interactions.

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.

Solubilization of spiropyran in aqueous NaBr solutions of dodecyltrimethylammonium bromide

1,3,3-Trimethylindolino-6′-nitrobenzopyrilospiran is solubilized in aqueous NaBr solutions of dodecyltrimethylammonium bromide (DTAB). The dye is soluble in solutions of DTAB having concentrations higher than the critical micelle concentration. The solubilization power of DTAB is 2.08·10 −3 mol dye per mol DTAB at NaBr concentrations lower than 1.84 M, while it increases linearly with increasing NaBr concentration from 1.84–4.50 M. The constant solubilization power of DTAE is attributable to the spherical micelles, while its higher solubilization power in the presence of NaBr beyond 1.84 M can be ascribed to rod-like micelles. The solubilization capacity of a spherical micelle of DTAB ranges from 0.11–0.18, depending on the NaBr concentration, where the micelle aggregation number varies from 52–86. The rod-like micelle has an increasing solubilization capacity with increasing NaBr concentration, and it can solubilize the dye to such an amount that 136 DTAB molecules along its contour length incorporate one dye molecule. The solubilized dye is partly in the mecrocyanine form, and the solubilization locus has polarity corresponding to a dielectric constant ≈35.

Miscibility of dodecyltrimethylammonium bromide and dodecyltrimethylammonium chloride in surface-adsorbed film and micelle

Surface tension of aqueous solutions of mixtures of dodecyltrimethylammonium bromide (DTAB) and dodecyltrimethylammonium chloride (DTAC) has been measured and analyzed by using thermodynamic relations. The adsorbed film has been found to contain more DTAB molecules than the solution. The shape formed by the curves of the total molality at constant surface tension against the solution and surface compositions indicates the ideal mixing of the DTAB and DTAC molecules in the adsorbed film. Micellar composition has been estimated at the critical micelle concentration (CMC). The micelles have been found to be richer in DTAB than the solution, but poorer in DTAB than the adsorbed film at the CMC. The DTAB and DTAC molecules have been shown to mix ideally in the micelles. From the comparison with the results on the system of decylammonium bromide and decylammonium chloride, it has been concluded that, on the mixing of surfactants differing only in counter ions, the adsorbed film is influenced more significantly by the ionic head group of the surfactant than the micelle.