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.     

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.     

Preferential adsorption of cationic surfactant mixture studied by bromide ion selective total-reflection XAFS measurement

The total-reflection XAFS measurement possessing bromide ion selectivity at the interfacial region was applied to the adsorbed film of hexadecyltrimethylammonium chloride (HTAC) and dodecyltrimethylammonium bromide (DTAB) mixture. The surface compositions XjH of individual ions j ( j = HTA+, Cl(-), DTA+, and Br (-)) were evaluated by combining the surface excess concentration of Br(-) estimated from the XAFS with the surface composition of the respective surfactants from the surface tension results. It is clearly shown that HTA+ and Br(-) are preferentially adsorbed to DTA+ and Cl(-) at the air/water interface. The preferential adsorption was estimated numerically in terms of activity coefficient fi+/-(H,p) of component i and excess Gibbs energy of adsorption ?prH,E. Then, the magnitude of ?prH,E was compared with that of ?prH,E attributable to intrinsic interaction between ions.     

Study on the distribution of binary mixed counterions in surfactant adsorbed films by total reflection XAFS measurements

The total reflection X-ray absorption fine structure (TR-XAFS) technique was applied to adsorbed films at the surface of aqueous solutions of surfactant mixtures composed of dodecyltrimethylammonium bromide (DTAB) and dodecyltrimethylammonium tetrafluoroborate (DTABF₄). The obtained XAFS spectra were expressed as linear combinations of two specific spectra corresponding to fully hydrated bromide ions (free-Br) and partially dehydrated bromide ions adsorbed to the hydrophilic groups of surfactant ions (bound-Br) at the surface. The ratio of free- and bound-Br ions was determined as a function of surface tension and surface composition of the surfactants. Taking also the results in our previous studies on the DTAB - dodecyltrimethylammonium chloride (DTAC) and 1-hexyl-3-methylimidazolium bromide (HMIMBr) - 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF₄) mixed systems into consideration, the relation between counterion distribution and miscibility of counterions at the solution surface was deduced for the surfactant mixtures having common surfactant ions but different counterions.     

ADSORPTION AND ASSOCIATION IN BINARY MIXTURES OF CATIONIC SURFACTANTS

The adsorption and solution properties of cationic surfactants dodecylammonium chloride, tetradecylammonium chloride, and hexadecylammonium chloride, as well as hexadecyltrimtehylammonium bromide in pure and mixed states, were studied by surface tension and conductance measurements. The surfactants mixed non-ideally in both mixed monolayer and in the mixed micelles. The regular solution theory was used for evaluating the non-ideal interactions between molecules in adsorbed and micellar states. Similar values of the mixed monolayer and mixed micelle molecular interaction parameters in a mixture imply the molecules at the interface and in the mixed micelle have similar interactions. No synergism in surface tension effectiveness was observed. The adsorbed film at the air/water interface and mixed micelles were richer in more surface-active component.     

Effects of alkyl chain length on synergetic adsorption and micelle formation in homologous cationic surfactant mixtures

The surface tensions (gamma) of the aqueous solutions of tetradecyltrimethylammonium bromide (TTAB) and dodecyltrimethylammonium bromide (DTAB) were measured as a function of the total molality of surfactants (m) and the relative proportion (composition) of DTAB (X(2)) at 298.15 +/- 0.05 K under atmospheric pressure. The effect of the difference in the hydrophobic chain length between hexadecyltrimethylammonium bromide (HTAB) and DTAB on the synergism was examined. This synergism was observed in the miscibility at the surface of a mixture of these two compounds. The excess Gibbs energy of adsorption of the TTAB-DTAB system was positive in contrast to the HTAB-DTAB system. This indicates that there are certain restrictions on the difference in the hydrophobic chain length for the synergism to be brought about in homologous cationic surfactant mixtures. This mechanism was explained by the theory of a staggered structure formation at the air/water interface. A similar argument successfully applied to the hexadecyltrimethylammonium chloride (HTAC)-dodecyltrimethylammonium chloride (DTAC) and tetradecyltrimethylammonium chloride (TTAC)-DTAC mixtures also.     

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 CH and CF chains became more influential in the expanded film within a restricted composition region, where it should be noted that the interaction between CH and CF is weaker than that between CH chains or between CF 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.     

Volume behavior of mixed micelles of dodecyltrimethylammonium chloride and bromide

Densities of aqueous solutions of mixtures of dodecyltrimethylammonium chloride (DTAC) and dodecyltrimethylammonium bromide (DTAB) have been measured as a function of total molality at constant composition and the apparent molar volumes of the mixtures were derived from the density data. The partial molar volumes of monomeric surfactant mixtures, the molar volumes of mixed micelles, and the volumes of formation of mixed micelles were evaluated and are compared with those for decyltrimethylammonium bromide (DeTAB) and DTAB mixtures. The partial molar volumes of monomeric surfactant mixtures and the molar volumes of mixed micelles are observed to depend linearly on the monomer and micelle compositions, respectively. Although the volume of formation of mixed micelles of the DeTAB-DTAB mixture depends on the micellar composition, that of the DTAC-DTAB mixture is observed to be almost independent of the micellar composition. This suggests that the volumes of the counter ions in the micellar solutions are almost equal to those in the monomeric solutions.     

全氟辛酸钠与十二烷基三甲基溴化铵混合胶束微环境性质的NMR,ESR研究

应用表面张力法、NMR法和ESR法研究了全氟辛酸钠(SPFO)-十二烷基三甲基溴化铵(DTAB)混合体系水溶液胶束形成及混合胶束的微环境性质(微观粘度、微观极性等)。结果表明, 碳氟表面活性剂碳氟链和碳氢表面活性剂碳氢链之间具有强烈的相互作用, DTAB与SPFO在水溶液中形成混合胶束。DTAB与SPFO混合体系的表面活性高于单一的DTAB或SPFO, 混合体系cmc较单一的DTAB和SPFO低。DTAB与SPFO混合胶束的微观粘度较DTAB胶束的大, 而微观极性较DTAB的小。     

Nonideal mixing of dodecyltrimethylammonium halides and nonionic surfactant in adsorbed films and micelles

The ion–dipole interaction between dodecyltrimethylammonium cations and nonionic surfactant molecules in adsorbed films and micelles was investigated by concentrating on the difference in the degree of counterion binding by employing dodecyltrimethylammonium chloride (DTAC)–octyl methyl sulfoxide (OMS) and dodecyltrimethylammonium bromide (DTAB)–OMS mixtures. The phase diagrams of adsorption and micelle formation were constructed and then the nonideal mixing of different species of surfactants was demonstrated in terms of the excess Gibbs free energies of adsorption and micelle formation, and the surface excess areas. Furthermore the dependence of them on the counterion was clearly shown. All these results were found to support our previous view that the direct interaction between surfactant cation and the dipole of the hydrophilic part of a nonionic surfactant is essential in cationic-nonionic surfactant mixtures, i.e., the DTAC system with a lower counterion biding has more negative excess thermodynamic quantities than the DTAB system with a higher one.     

The Adsorption of Dodecyltrimethylammonium Bromide on Mica in Aqueous Solution Studied by X-Ray Diffraction and Atomic Force Microscopy

The adsorption of dodecyltrimethylammonium bromide (DTAB) onto natural muscovite mica and a synthetic expandable mica (EM) in aqueous solution has been investigated using both microscopic and macroscopic surface characterization techniques. The electrokinetic properties of the surfaces were monitored as a function of the concentration of DTAB using atomic force microscopy and microelectrophoresis. The adsorption isotherm of DTAB on EM was measured up to a solution concentration just below the critical micelle concentration of the surfactant. The thickness of the adsorbed layer on EM was determined using X-ray diffraction. Results indicate that the adsorbed layer consists of molecules lying quite flat on the mica surface at low concentrations and adsorbed in interleaved aggregate structures at concentrations approaching the critical micelle concentration of the surfactant in solution. Copyright 2001 Academic Press.     

Laterally nanostructured adsorbed layers of surfactant/surfmer mixtures before and after polymerisation

The adsorbed layer structure of mixed films of the polymerisable cationic surfactant dodecyldimethyl(ethylmethacrylate)ammonium bromide (MEDDAB) with the cationic and non-ionic surfactants dodecyltrimethylammonium bromide (DTAB) and polyoxyethylene-23-lauryl ether (C12E23) has been investigated by AFM soft-contact imaging before and after solution polymerisation of MEDDAB. MEDDAB alone adsorbs on mica as a planar bilayer, but the adsorbed layer structure can be modified by mixing with DTAB or C12E23 to yield an adsorbed mesh or cylinders. The equilibrium adsorbed film structure after solution polymerisation of the methacrylate group on MEDDAB was found to depend on the solubilising ability of the non-polymerisable surfactant. C12E23 effectively prevented precipitation of polymerised MEDDAB, retaining the unpolymerised adsorbed layer structure, whereas DTAB mixtures became cloudy above 23 mol% MEDDAB. The resultant structure remained similar to the adsorbed rods formed prior to polymerisation, but had a diameter several times larger.     

Miscibility of calcium chloride and sodium dodecyl sulfate in the adsorbed film and aggregates

The adsorption, micelle formation, and coagel-particle formation of sodium dodecyl sulfate in the presence of calcium chloride were studied from the viewpoint of mixed adsorption and aggregate formation of inorganic salt and surfactant. Judging from the phase diagrams of adsorption and aggregate formation, negative azeotropy takes place in the mixed adsorption and aggregate formation of calcium chloride and sodium dodecyl sulfate due to electrostatic attraction between calcium and dodecyl sulfate ions. The miscibility of calcium chloride and sodium dodecyl sulfate in the oriented states increases in the order, particle > adsorbed film > micelle. The difference in the miscibility was ascribed to the difference in geometry between the adsorbed film and micelle and to the interaction between bilayer surfaces in the particle. The particle-micelle equilibrium was thermodynamically considered by using the equilibrium composition of aggregates.     

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.     

Miscibility of sodium chloride and sodium dodecyl sulfate in the adsorbed film and aggregate

The adsorption, micelle formation, and salting out of sodium dodecyl sulfate in the presence of sodium chloride were studied from the viewpoint of their mixed adsorption and aggregate formation. The surface tension of aqueous solutions of a sodium chloride–sodium dodecyl sulfate mixture was measured as a function of the total molality and composition of the mixture. Phase diagrams of adsorption and aggregate formation were obtained by applying thermodynamic equations to the surface tension. Judging from the phase diagrams, sodium chloride and sodium dodecyl sulfate are miscible in the adsorbed film at very large composition of sodium chloride and in the salted-out crystalline particle, while they are immiscible in the micelle. The miscibilities in the adsorbed film, micelle, and crystalline particle increase in the following order: particle > adsorbed film > micelle. The difference in miscibility among the oriented states was ascribed to the difference in geometry between the adsorbed film and micelle and to the interaction between bilayer surfaces in the particle.     

Charge number effect on the miscibility of inorganic salt and surfactant in adsorbed film and micelle: inorganic salt-octyl methyl sulfoxide mixtures

Adsorption and micelle formation of a surfactant in the presence of inorganic salts with different charge numbers of cations were investigated from the viewpoint of mixed adsorption and micelle formation of salt and surfactant. Surface tension of aqueous solutions of the mixtures of octyl methyl sulfoxide (OMS) with calcium chloride and lanthanum chloride was measured as a function of the total molality of the mixture and the mole fraction of OMS in the mixture at 298.15 K under atmospheric pressure. Composition of the adsorbed film and micelle was numerically evaluated from the dependence of the total molality at a given surface tension and the mixture CMC on the bulk composition to draw phase diagrams of adsorption and micelle formation. Judging from the phase diagrams together with the ones of the sodium chloride system, miscibility of inorganic salt and OMS in the adsorbed film and micelle increases with an increase in the charge number of inorganic cation, which is attributable to the attractive interaction between inorganic cation and the polar head group of OMS molecule in the adsorbed film and micelle.     

Specific counterion effect on the adsorbed film of cationic surfactant mixtures at the air/water interface

To investigate the counterion effects, we employed dodecyltrimethylammonium bromide (DTABr)-dodecyltrimethylammonium tetrafluoroborate (DTABF(4)) mixed aqueous solutions and measured their surface tensions, then analyzed these data in a thermodynamic treatment. The tensiometry showed that DTABF(4) was more effective in lowering the surface tension of water. The phase diagram of adsorption demonstrated that the surface was enriched with BF(4)(-) ions, but the composition of Br(-) ions in the adsorbed film was slightly enhanced compared to the ideal mixing criteria. These were explained in terms of the size and polarizability of counterions. Moreover, the distribution of counterions of the DTABr-DTABF(4) mixtures in the adsorbed film is greatly different from that of the 1-hexyl-3-methylimidazolium bromide (HMIMBr)-1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF(4)) mixtures, where a stronger hydrogen-bonding exists between BF(4)(-) and HMIM(+) ions. These findings suggest that the adsorption of counterions in electric double layers is likely subject to two factors: the nature of counterion and their interactions with surfactant ions.     

Study on surface adsorption from cationic surfactant–electrolyte mixed aqueous solution including BF 4 − ion

The surface tension of aqueous mixtures of dodecyltrimethylammonium tetrafluoroborate (DTABF₄) and sodium tetrafluoroborate (NaBF₄) was measured as a function of total molality and composition of DTABF₄ at 298.15 K. The results were analyzed by originally developed thermodynamic equations and compared with those of dodecyltrimethylammonium bromide (DTAB)–sodium bromide (NaBr) mixed system. It was indicated that BF₄⁻ ions reduce the repulsion between DTA⁺ ions more effectively than Br⁻ ions in the adsorbed film. To investigate this difference more closely, the surface tension of DTAB–NaBF₄ and DTABF₄–NaBr mixed system was also measured. The data analysis revealed that BF₄⁻ ions are adsorbed positively even for the pure NaBF₄ system and preferentially to Br⁻ ions in these mixtures. Furthermore, it was concluded that the side-by-side arrangement suggested in the adsorbed film of 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF₄) is due to not only the positive adsorption of BF₄⁻ ions but also the capability of hydrogen bond formation between imidazolium ion and BF₄⁻ ions.     

Studies of mixed micelle formation between cationic gemini and cationic conventional surfactants

Mixed micellization of dimeric cationic surfactants tetramethylene-1,4-bis(hexadecyldimethylammonium bromide)(16-4-16), hexamethylene-1,6-bis(hexadecyldimethylammonium bromide) (16-6-16) with monomeric cationic surfactants hexadecyltrimethylammonium bromide (CTAB), cetylpyridinium bromide (CPB), cetylpyridinium chloride (CPC), and tetradecyltrimethylammonium bromide (TTAB) have been studied by conductivity and steady-state fluorescence quenching techniques. The behavior of mixed systems, their compositions, and activities of the components have been analyzed in the light of Rubingh's regular solution theory. The results indicate synergism in the binary mixtures. Ideal and experimental critical micelle concentrations (i.e., cmc(*) and cmc) show nonideality, which is confirmed by beta values and activity coefficients. The micelle aggregation numbers (N(agg)), evaluated using steady-state fluorescence quenching at a total concentration of 2 mM for CTAB/16-4-16 or 16-6-16 and 5 mM for TTAB/16-4-16 or 16-6-16 systems, indicate that the contribution of conventional surfactants was always more than that of the geminis. The micropolarity, dielectric constant and binding constants (K(sv)) of mixed systems have also been evaluated from the ratios of respective peak intensities (I(1)/I(3) or I(0)/I(1)).     

Effect of adsorbed layer surface roughness on the QCM-D response: focus on trapped water

The effect of surface roughness on the quartz crystal microbalance with dissipation monitoring (QCM-D) response was investigated with emphasis on determining the amount of trapped water. Surfaces with different nanoroughnesses were prepared on silica by self-assembly of cationic surfactants with different packing parameters. We used surfactants with quaternary ammonium bromide headgroups: the double-chained didodecyltrimethylammonium bromide (C12)2DAB (DDAB), the single-chained hexadecyltrimethylammonium bromide C16TAB (CTAB), and dodecyltrimethyl-ammonium bromide C12TAB (DTAB). The amount of trapped water was obtained from the difference between the mass sensed by QCM-D and the adsorbed amount detected by optical reflectometry. The amount of water, which is sensed by QCM-D, was found to increase with the nanoroughness of the adsorbed layer. The water sensed by QCM-D cannot be assigned primarily to hydration water, because it differs substantially for adsorbed surfactant layers with similar headgroups but with different nanoscale topographies.