Dodecyltrimethylammonium Bromide Concentration Research Articles

Observation of Electrostatically Driven Surface Adsorption in Mixed Surfactant Systems.

We employed heterodyne-detected vibrational sum-frequency generation (HD-VSFG) spectroscopy to obtain a molecular-level understanding of the interaction between the anionic surfactant sodium dodecyl ammonium sulfate (SDS) and the cationic surfactant dodecyltrimethylammonium bromide (DTAB). We observed that these surfactants show a strong cooperative effect on their adsorption to the water-air interface. Even at bulk concentrations 1000 times lower than the critical micelle concentrations of SDS and DTAB, a nearly complete surface surfactant layer is observed when both surfactants are present. This strong enhancement of the surface concentrations of DS- and DTA+ can be quantitatively explained from the favorable Coulomb interaction of the oppositely charged headgroups of DS- and DTA+ and the electrostatic interactions with their counterions. The HD-VSFG results are complemented by a modified Langmuir adsorption model in which we include the free energy associated with the electrostatic interactions of the surfactant ions and their counterions.

Role of Alkyl Chain Length in Surfactant-Induced Precipitation of Reactive Brilliant Blue KN-R

To develop a cost-effective method for the effective removal of reactive brilliant blue KN-R (RBB KN-R) from wastewater, we investigated the interactions between RBB KN-R and three cationic surfactants with different alkyl chain lengths, namely dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB), and cetyltrimethylammonium bromide (CTAB). Employing a conductivity analysis, surface tension analysis, ultraviolet-visible spectrophotometry, and molecular dynamics simulation, we ascertained that RBB KN-R formed a 1:1 molar ratio dye–surfactant complex with each surfactant through electrostatic attraction. Notably, an augmentation in alkyl chain length correlated with increased binding strength between RBB KN-R and the surfactant. The resulting dye–surfactant complex exhibited heightened surface activity, enabling interactions through hydrophobic forces to generate dye–surfactant aggregates when the molar ratio was below 1:1. Within these mixed aggregates, self-assembly of RBB KN-R molecules occurred, leading to the formation of dye aggregates. Due to the improved hydrophobicity with increased alkyl chain length, TTAB and CTAB could encapsulate dye aggregates within the mixed aggregates, but DTAB could not. The RBB KN-R aggregates tended to distribute on the surface of the RBB KN-R-DTAB mixed aggregates, resulting in low stability. Thus, at a DTAB concentration lower than CMC, insoluble particles readily formed and separated from surfactant aggregates at an RBB KN-R and DTAB molar ratio of 1:4. Analyzing the RBB KN-R precipitate through scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) and measuring the DTAB concentration in the supernate revealed that, at this molar ratio, all RBB KN-R precipitated from the dye–surfactant mixed solution, with only 7.5 ± 0.5% of DTAB present in the precipitate. Furthermore, the removal ratio of RBB KN-R reached nearly 100% within a pH range of 1.0 to 9.0 and standing time of 6 h. The salt type and concentration did not significantly affect the precipitation process. Therefore, this simultaneous achievement of successful RBB KN-R removal and effective separation from DTAB underscores the efficacy of the proposed approach.

Evolution of the structure and interaction in the surfactant-dependent heat-induced gelation of protein.

The addition of a surfactant and/or an increase in temperature disrupt the native structure of proteins, where high temperature further results in protein gelation. However, in a mixed protein-surfactant system, surfactant concentration and temperature have been observed to exhibit both mutually associative and counter-balancing effects towards heat-induced gelation of protein-surfactant dispersion. This study is conducted on globular bovine serum albumin (BSA) protein and cationic surfactant dodecyl trimethyl ammonium bromide (DTAB), which interact strongly owing to their oppositely charged nature. The findings reveal that the BSA-DTAB suspension undergoes gelation with increasing temperature but only at lower concentrations of DTAB, where the presence of the surfactant facilitates gelation (associative effect). Conversely, as the surfactant concentration increases beyond a critical value, temperature-driven gelation of the BSA-DTAB system is completely inhibited, despite surfactant-induced protein denaturation (counter-balancing effect). To conceptualize these results, we compared them with observations made in a system comprising protein and a similarly charged surfactant, sodium dodecyl sulfate (SDS). It has been further demonstrated that the anionic surfactant (SDS) can restrict protein gelation at much lower concentration compared to the cationic surfactant (DTAB). The evolution of the structure and interaction during gel formation/inhibition has been examined to understand the underlying mechanism guiding these sol-gel transitions. We present a comprehensive phase diagram, encompassing the solution/gel states of the protein-surfactant dispersion, with respect to the dispersion temperature, surfactant concentration, and ionic behavior (anionic or cationic) of the surfactants.

Solubilization and remediation of polycyclic aromatic hydrocarbons in groundwater by cationic surfactants coupled nanobubbles: Synergistic mechanism and application

Polycyclic aromatic hydrocarbons pose a severe threat to groundwater and the soil environment. Improving the efficiency of the surfactant-enhanced remediation (SER) technique is a research hotspot. Nanobubbles (NBs) were introduced to enhance the solubilization effect of cationic surfactant dodecyltrimethylammonium bromide (DTAB) on phenanthrene (PHE). The interaction between NBs and DTAB was favorable in reducing the critical micelle concentration of DTAB. The equilibrium solubilization of DTAB to PHE was upgraded by up to 30.4% with the synergy of NBs. The effect of DTAB concentration on the stability of NBs was an essential reason for the different upgrade rates. The kinetic study showed that the process of equilibrium solubilization was accelerated, while NBs were “consumed”. Based on the classic DLVO framework, OH– and inorganic ions in groundwater can participate in the formation of micelles and change the double electric layer thickness of bubbles, which are the key factors affecting the stability of NBs. The results revealed the colloidal interface characteristics and the particle behavior of micelles with NBs, providing new insight into the combined application of micelles or vesicles with NBs.

Micellization pattern of cationic surfactants in presence of azo dye in methanol mixed media

Conductivity measurements at three different temperatures (298.15, 308.15, and 318.15 K) were performed to determine the micellization nature of cationic surfactants, i.e., dodecyl trimethylammonium bromide (DTAB) and cetylpyridinium chloride (CPC), in the absence and presence of the azo dye methyl red (MR) in four mixed solvent systems (0.1 to 0.4) volume fraction of methanol in water. We calculated the critical micelle concentration (CMC) of DTAB and CPC and the degree of ionization (α) for both in the absence and presence of MR using William’s method. The interaction of surfactants DTAB and CPC with MR has been identified separately through the dye-surfactant aggregation process, with reduced CMC values due to the molecular reorientation of methyl red in the systems. Micellization becomes more likely with MR due to the formation of a molecular complex in mixed systems. We calculated different thermodynamic properties both in the absence and presence of methyl red. Such parameters are the standard Gibbs free energy of micellization (ΔGmo), the standard enthalpy of micellization (ΔHmo), the standard entropy of micellization (ΔSmo), the standard free energy of transfer (ΔGtranso) and heat capacity of micellization (ΔmCp0). In accordance with ΔGmo values, the mixtures show the spontaneous nature of micellization of DTAB and CPC with MR as well.

Comparative study of the co-assembly behaviour of 3-chloro-4-hydroxy-phenylazo dyes with DTAB.

The co-assembly of three one-fold negatively charged 3-chloro-4-hydroxy-phenylazo dyes (Yellow, Blue and Red) with the cationic surfactant dodecyltrimethylammoniumbromide (DTAB) was studied to probe dye-DTAB binding stoichiometry and assembly morphology. For each dye, phase separation was observed above a given dye : DTAB ratio with the ratio depending on the dye. While Yellow and DTAB showed liquid/liquid phase separation above Yellow : DTAB = 1 : 1.67, crystalline dye-DTAB complexes were observed for Blue-DTAB and Red-DTAB above Blue : DTAB = 1 : 2.56 and Red : DTAB = 1 : 2.94 respecively. In homogeneous solution, UV/vis spectroscopic investigations suggest stochiometries of Yellow : DTAB = 1 : 2, Blue : DTAB = 1 : 3 and Red : DTAB = 1 : 4. It was concluded, that Yellow exhibits the highest dye : DTAB binding stoichiometry in both, dye-surfactant complexes in the 2-phase region and in solution, whereas the lowest dye : DTAB binding stoichiometry was observed for Red-DTAB in both cases. The observed stoichiometries are inversely correlated to the impact dye addition has on the morphology of DTAB micelles. Generally, addition of dye to DTAB micelles leads to a reduction in spontaneous curvature of these micelles and to the formation of triaxial ellipsoidal or cylindrical micelles from oblate ellipsoidal DTAB micelles. At a DTAB concentration of 30 mM and a dye concentration of 5 mM, this effect was most pronounced for Red and least pronounced for Yellow, whilst Blue showed an intermediate effect.

Pickering Emulsions Stabilized by Mesoporous Nanoparticles with Different Morphologies in Combination with DTAB.

The morphology of nanoparticles plays a significant role in the properties and applications of Pickering emulsions. Oil-in-water (O/W) Pickering emulsions were prepared using spherical, rod-like, and thread-like mesoporous silica nanoparticles (MSNPs) in combination with the cationic surfactant dodecyltrimethylammonium bromide (DTAB) as a stabilizer. The effects of nanoparticle morphology on the stability and stimuli-responsive properties of Pickering emulsions were investigated. For spherical and rod-like MSNP systems, stable Pickering emulsions were obtained at DTAB concentrations above 0.2 mmol·L–1. Stable Pickering emulsions containing thread-like MSNPs were produced at lower DTAB concentrations of approximately 0.1 mmol·L–1. The droplets with thread-like MSNPs were extremely large with an average diameter around 700 μm at DTAB concentrations of 0.1–0.3 mmol·L–1, which were approximately 20 times larger than those of conventional droplets. Scanning electron microscopy (SEM) images showed that all three types of MSNPs were located at the O/W interfaces. Irrespective of the morphology of the MSNPs, all the stable Pickering emulsions retained their original appearance for more than 6 months. By adding NaOH and HCl alternatively, the Pickering emulsions containing spherical and rod-like MSNPs could be switched between unstable and stable states more than 60 times. The Pickering emulsions containing thread-like MSNPs, by contrast, could have their droplet size switched between large and small more than 10 times without any obvious phase separation. The high anisotropy of thread-like MSNPs contributed to the low interface curvature of the droplets. This study revealed the relationship between the morphology of MSNPs and the characteristics of Pickering emulsions. These results enrich our knowledge about the formulation of Pickering emulsions and expand their applications.

Adsorption behaviors and emission properties of p-sulfonatocalixarene/ammonium-based surfactant systems: A comparison between the effects of gemini surfactant and its corresponding monomeric surfactant

So far, the research on calixarene/surfactant systems has been mainly focused on their aggregation characteristics due to their potential applications as stimuli-responsive systems, while the reports about their absorption behavior and spectroscopic properties have been limited. Understanding basic properties of supra-amphiphilic molecules is of great significance to improve their application performance and expand their application potential. In the present study, the interactions of p-sulfonatocalix[n]arenes (SC[n], n = 4, 6 and 8) with the cationic surfactants (including dodecyltrimethyl ammonium bromide (DTAB), pentamethylene-1,5-bis (dimethyldodecyl ammonium bromide) (12-5-12), and octamethylene-1,8-bis(dimethyldodecyl ammonium bromide (12-8-12)) were studied by measuring surface tension, fluorescence spectra and 1H NMR spectra. It was found that SC[n] changed the absorption behaviors of 12-s-12 (s = 5 and 8) and DTAB at air/water surface in different ways. In the presence of SC[n], the value of γ for 12-s-12 remains almost constant until 12-s-12 content reaches C1, then decreases sharply until C2, followed by a slow decrease up to the CMC. The surface tension of DTAB/SC[n] solution begins to decrease at a very low concentration of DTAB until Ca, followed by a short plateau until Cb, and then, the surface tension increases sharply until Cc, after which, the surface tension curve gradually overlaps with that of single DTAB solution. Meanwhile, the binding of SC[n] with these surfactants makes SC[n] emit fluorescence, and the quantum yields for SC[n]/12-s-12 systems are higher than those for SC[n]/DTAB systems. Supra-amphiphiles have been expected as smart materials. This study may provide meaningful information for application of calixarene-based supra-amphiphiles.

Interaction of crystal violet dye with dodecyltrimethylammonium bromide in aqueous and electrolyte medium at different temperatures

Dyeing is one of the most important processes in the textile industries which require optimum binding of dye with the fabrics. In the binding phenomenon of dye with the fabrics, surfactants play a significant role. The presence of different auxiliaries modifies the dye-surfactant interaction which can influence the binding of dye with the fabrics. Herein, we studied the interaction of crystal violet (CV) dye with a cationic surfactant, dodecyltrimethylammonium bromide (DTAB) conductometrically in absence and presence of electrolytes (NaBr, Na2SO4, and Na3PO4). The critical micelle concentration (cmc) of DTAB was found to dwindle with the boost of concentration of CV. The cmc of CV + DTAB mixtures were monotonically increased with the increase of temperature. The presence of electrolytes facilitates the micellization of CV + DTAB mixture. The values of counterion binding were found to be augmented with the augmentation of temperature in aqueous and NaBr media while the opposite trend was observed in Na2SO4 and Na3PO4 media. The Gibbs free energy of micellization (ΔGm0) were found to be negative in all cases. The enthalpy (ΔHm0) and entropy (ΔSm0) of micellization were negative and positive in aqueous, NaBr, and Na2SO4 media while both values were positive in Na3PO4 medium. The enthalpy–entropy compensation parameters suggest that the most stable micelle of CV + DTAB is formed in Na2SO4 medium.

Interfacial complexation of a neutral amphiphilic ‘tardigrade’ co-polymer with a cationic surfactant: Transition from synergy to competition

HypothesisNeutral amphiphilic PEG-g-PVAc co-polymer (a “tardigrade” polymer consisting of a hydrophilic polyethylene glycol, PEG, backbone with hydrophobic polyvinyl acetate, PVAc, grafts) can form complexes at the air–water interface with cationic dodecyltrimethylammonium bromide (DTAB) via self-assembly. Compared to anionic SDS, cationic DTAB headgroups are expected to interact strongly with the negatively charged OH– groups from the partial dissociation of the PVAc grafts. We anticipate a transition from synergistic to competitive behaviour, which is expected to be dependent on the surfactant structural characteristics and concentration. ExperimentsDTAB/PEG-g-PVAc mixtures were investigated using a combination of dynamic and equilibrium surface tension measurements, neutron reflectivity (NR) at the air–water interface, and foaming tests. We varied the concentrations of both the DTAB (0.05 to 5 critical micelle concentration, cmc) and that of PEG-g-PVAc (0.2 and 2 critical aggregation concentration, cac). FindingsOur results show that the interfacial interactions between DTAB and PEG-g-PVAc were both synergistic and antagonistic, depending sensitively on the surfactant concentration. At DTAB concentrations below its cmc, a pronounced cooperative adsorption behaviour was likely driven by the hydrophobic interactions between the DTAB tail and the PVAc grafts and the attraction between the DTAB headgroups and the partially dissociated –O- groups in the partially hydrolysed PVAc grafts, forming a mixed layer. This synergistic adsorption behaviour transitioned to a competitive adsorption behaviour at DTAB concentrations above its cmc, leading to polymer-surfactant partition, forming a “hanging” polymer layer underlying a surfactant monolayer at the interface. We postulate that DTAB/PEG-g-PVAc complexation in the bulk contributed to partial depletion of the mixture from the interface. We therefore consider this polymer/surfactant system to be a moderately interacting system at the air–water interface. No discernible differences in the foaming behaviour were observed between the DTAB/PEG-g-PVAc systems and the pure surfactant. Our results suggest that surfactant headgroup characteristics (particularly charges) were crucial in determining the structure and composition of polymer-surfactant complexes at the air–water interface, as well as the foamability and foam stability, whilst the coexistence of the synergistic and competitive adsorption behaviour is attributed to the unique architecture of the tardigrade polymer with amphiphilicity and partial charge, facilitating different surfactant-polymer interactions at different DTAB concentrations.

A simulation study of self-assembly behaviors and micellization properties of mixed ionic surfactants

The simulation and micellization studies of dodecyltrimethylammonium bromide (DTAB) and sodiumdodecyl sulfate (SDS) mixed surfactant systems in an aqueous medium are noted. The critical micelle concentration (CMC) of mixed surfactants and different bulk properties were determined by using viscosity data. The physicochemical properties infer the various structural activities in ionic interaction, hydrogen bonding, London dispersive forces, activation energy, surface energy, van der Waal forces, ion-hydrophilic and ion-hydrophobic, and others. The synergistic interaction was observed in the mixed surfactants system, and the activity coefficients were compared with the different theoretical models. A refractometric study of anionic-rich and cationic-rich in the presence and absence of Methylene Blue (MB) and Methyl orange (MO) in aqueous solutions is carried out at T = 298.15 K. The study of spectrum of single and mixed surfactants at the CMC level through the attenuated total reflection-Fourier transform infrared (ATR-FTIR)spectroscopy based on change frequency are discussed.The phase behavior of DTAB concentrations were varied from 0.0001 to 0.03 mol∙L-1 with 0.01 mol∙L-1 SDS (DTAB-rich), and SDS concentration from 0.001 to 0.015 mol∙L-1 with 0.005 mol∙L-1 DTAB (SDS-rich).

Molecular dynamics simulation studies on the concentration-dependent interaction of dodecyltrimethylammonium bromide with curcumin

Curcumin, a natural dietary polyphenol extracted from the roots of the plant Curcumin longa, possesses diverse therapeutic effects. The poor water solubility and instability of curcumin can be improved by encapsulation in surfactant micelles. In this paper, the interaction between curcumin and dodecyltrimethylammonium bromide (DTAB) in aqueous solution was studied by molecular dynamics simulation. Three systems were established by changing the number of added DTAB molecules to explore the interaction mode between curcumin and DTAB in different aggregation states. Distance distribution, number density distribution, electrostatic potential distribution and decomposition of energy were used to clarify binding structures and interaction mechanism. Before forming micelles, changes in the concentration of DTAB resulted in the formation of two different aggregation states, namely monomer and pre-micelle state. DTAB of two different aggregation states interacted with curcumin through electrostatic and hydrophobic interactions, respectively. When the surfactant concentration was above the critical micelle concentration (cmc), curcumin was solubilized into the micelle and located at the palisade layer as expected. The dynamic simulation results can provide a theoretical basis for experimental research and explain the interaction mode between them at the microscopic level. This will provide guidance for the use of surfactants in pharmaceutical formulations.

Retention and Partition Behaviors of Solutes in a Surfactant-Based Mobile Phase at Concentrations Approaching the Critical Micelle Concentration in Liquid Chromatography

Previously developed three-phase retention model has been extensively used to understand the partition behaviors of solutes in micellar liquid chromatography (MLC). The model has been used to explain the linear plots of the reciprocal of the solute retention factor versus the micelle concentration in the mobile phase. Because a phase equilibrium model of micellization is assumed, the retention model is generally applied to systems at surfactant concentrations above the critical micelle concentration (CMC). This study investigated the retention behaviors of five solutes, namely acetone, benzaldehyde, acetophenone, benzene, and benzyl alcohol, as a function of the concentration of dodecyltrimethylammonium bromide (DTAB) in water on a C18 sorbent. Distinct retention behaviors were observed for DTAB concentrations below and above the CMC, which have not been adequately explained by the retention models described in the literature. Thus, a new MLC retention model based on a mass action model of micellization was developed herein. Retention and partition behaviors were found to be determined by three key dimensionless groups, representing the partition coefficients of the solutes between the DTAB-uncomplexed aqueous phase and the stationary, DTAB-complexed aqueous, and micellar phases. Thermodynamic equilibrium constants were estimated from fitting the model to the retention factor data. The new model showed a good fit to the HPLC data below and above the CMC and was reliable for describing the transition of distinct retention behaviors near the CMC.

Anomalous Variation of Excited-State Proton Transfer Dynamics inside a Triblock Copolymer-Cationic Surfactant Mixed Micelle.

Mixed micelles formed by triblock copolymers [poly(ethylene oxide)m (EOm)-poly(propylene oxide)n (POn)-EOm] with various surfactants have widespread applications. Molecular-level understanding of the composition, interfacial organization, and hydration of the copolymer-surfactant mixed micelle is greatly necessary from application perspectives. Here, we applied 8-hydroxypyrene-1,3,6-trisulfonate (HPTS) to probe the mixed micelle of a triblock copolymer F127 (EO101-PO56-EO101) and a cationic surfactant dodecyltrimethylammonium bromide (DTAB) at various compositions. The emission spectrum of HPTS modulates anomalously with the variation of DTAB concentration, displaying at least four regimes. The ratio of the emission intensities of the two bands (protonated/deprotonated) (1) first increases steeply in the low-concentration range (0.1-6 mM), (2) remains almost steady at the intermediate concentration (8-20 mM), (3) decreases at high concentration (20-80 mM), and (4) finally, remains almost constant at a very high concentration (100-400 mM) of DTAB. Time-resolved measurements confirm that excited-state proton transfer dynamics varies unusually with the concentration of DTAB in the mixed micelle; substantial retardation is observed up to ∼12 mM, but after that, the dynamics becomes somewhat faster upon further addition. The rotational dynamics of a methoxy analogue of HPTS, 8-methoxypyrene-1,3,6-trisulfonate, becomes slower up to ∼12 mM DTAB and after that becomes faster at higher concentration. Moreover, dynamic light scattering measurements showed that the size of the mixed micelle decreases sharply in the low-concentration region (<20 mM DTAB) but decreases moderately at high concentration. Thus, the nature of the mixed micelle is very different at low and high concentrations of DTAB. At low concentration, the incorporation of DTAB results in a more compact and less hydrated mixed micelle, whereas a more hydrated and less organized assembly is formed at high concentration of DTAB.

Matte photographic paper as a low-cost material for metal ion retention and elemental measurements with laser-induced breakdown spectroscopy

Matte photographic paper was explored as a low-cost material for metal-ion retention. The extraction was promoted by ultrasound, the mechanical waves of which forced adhesion to the photographic paper surface of an ion pair formed by DTAB (dodecyltrimethylammonium bromide) with the anionic coordination complex formed by metal ions and SPADNS (1,8-dihydroxy-2-(4-sulfophenylazo)naphthalene-3,6-disulfonic acid trisodium salt). As a proof of concept, the migration of copper ions present in aqueous solution to the solid phase and their direct measurement by laser-induced breakdown spectroscopy (LIBS) was evaluated. The main parameters that affected the extraction (paper type and sonication time) and analyte detection in the solid phase (delay, spot size and accumulated number of pulses) were optimised in a univariate way. The conditions influencing the complexation reaction and formation of the ion pair in aqueous solution (pH and copper, SPADNS and DTAB concentrations) were set according to a previous study. Under the optimised conditions, it was possible to use this extraction technology as an alternative in determining copper content in aqueous solutions by LIBS, overcoming the intrinsic difficulties of this instrumental technique in the analysis of liquid samples. The calibration curves were obtained in a linear range of 0.50–7.50 mg L−1 copper in solution, with detection and quantification limits estimated at 0.08 and 0.24 mg L−1, respectively. The precision of the method was less than 4.3% and the accuracy was checked by spike and recovery tests on liquid samples with different chemical compositions and by comparison of LIBS results with graphite furnace atomic absorption spectrometry data. The potential of the proposed method for extraction of Al3+, Ag+, Fe3+, Mn2+, Ni2+ and Zn2+ was also evaluated and adequate extraction efficiencies were obtained. The proposed method stands out due to its low cost and ease of execution.

Molecular Interactions Leading to the Coadsorption of Surfactant Dodecyltrimethylammonium Bromide and Poly(styrenesulfonate) at the Oil/Water Interface.

The strong synergistic adsorption of mixed polymer/surfactant (P/S) systems at the oil/water interface shows promise for applications such as oil remediation and emulsion stabilization, especially with respect to the formation of tunable mesoscopic multilayers. There is some evidence that a combination of dodecyltrimethylammonium bromide (DTAB) and sodium poly(styrenesulfonate) (PSS) exhibits the adsorption of a secondary P/S layer, though the structure of this layer has long eluded researchers. The focus of this study is to determine whether the DTAB-assisted adsorption of PSS at the oil/water interface occurs as a single layer or with subsequent multilayers. The study presented uses vibrational sum-frequency spectroscopy and interfacial tensiometry to determine the degree of PSS adsorption and orientation of its charged groups relative to the interface at three representative concentrations of DTAB. At low and intermediate DTAB concentrations, a single mixed DTAB/PSS monolayer adsorbs at the oil/water interface. No PSS adsorbs above the system critical micelle concentration. The interfacial charge is found to be similar to that of P/S complexes solvated in the aqueous solution. The surface adsorbate and P/S complexes in the bulk both exhibit a charge inversion at around the same DTAB concentration. This study demonstrates the importance of techniques which can differentiate between coadsorbing species and calls into question current models of P/S adsorption at an oil/water interface.

An Interaction of Anionic- and Cationic-Rich Mixed Surfactants in Aqueous Medium through Physicochemical Properties at Three Different Temperatures

The mixed micellization of aqueous binary mixtures of DTAB-rich and SDS-rich surfactants, comprising sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) is studied in aqueous solution by using the physicochemical properties (PCPs) at three different temperatures (T = 293.15, 298.15, and 303.15 K) andP=0.1 MPa. The DTAB concentration is varied from 0.0001 to 0.03 M/mol·L−1in the ∼0.01 M/mol·L−1SDS solution, while the concentration of SDS is varied from 0.001 to 0.015 M/mol·L−1in the ∼0.005 M/mol·L−1DTAB. The stable formulations have been obtained by employing the DTAB-rich and SDS-rich surfactants solutions in 3 : 1 ratio. Therefore, different phases and aggregated states formed in the ternary combinations of DTAB/SDS/H2O have been identified and described. The calculated PCPs have been utilized for determining the nature of the solute-solvent interaction (SLS0I). With increasing surfactants concentration, the polarisation of the solution also increases along with an increase in relative viscosity (ηr), viscous relaxation time (τ), and surface excess concentration (Γmax). However, the surface area of the molecule (Amin), hydrodynamic volume (Vh), and hydrodynamic radius (Rh) decrease along with an increase in surfactants concentration.

Solid-like film formed by nano-silica self-assembly at oil–water interface

Nanoparticles have been widely investigated in enhancing oil recovery for unique interfacial properties. Bare nano-silica (NS) cannot be easily adsorbed at the interface due to a large number of hydroxyls on its surface. In this study, NS was decorated by dodecyl trimethyl ammonium bromide (DTAB), forming NS–surfactant via electrostatic force. In order to investigate the interfacial behavior of NS–surfactant at the oil-water interface, experiments and molecular dynamics simulations were conducted. Results indicated that NS–surfactant can self-assemble at the oil-water interface and solid-like films were observed, which contributed to 10.4% oil recovery of NS–surfactant flooding relative to water flooding. DTAB concentration, pH and NaCl were used to regulate the interfacial behavior of NS–surfactant. Interfacial tension decreased and surface coverage increased with DTAB concentration increase due to more NS–surfactant arranged at oil-water interface. NS–surfactant could arrange at the oil-water interface more closely through increase zeta potential, which could be achieved by adjusting pH and adding NaCl. Lower interfacial tension and higher surface coverage was observed under weakly acidic conditions. The addition of NaCl could greatly reduce the interfacial tension and increase the surface coverage.

Enhancement of the surface hydrophobicity of low-rank coal by adsorbing DTAB: An experimental and molecular dynamics simulation study

This study investigated the mechanism of improving the surface hydrophobicity of low-rank coal by adsorbing dodecyltrimethylammonium bromide (DTAB). Experimental tests were conducted to analyze the adsorption characteristic of DTAB on the coal surface including the adsorption amount, Zeta potential, wetting heat, and X-ray photoelectron spectroscopy measurement. Furthermore, the adsorption configuration, spatial location of the simulation systems, and the coal–water interaction were investigated by molecular dynamics (MD) simulation at the atomic scale. Experimental results indicate that the hydrophobicity of the low-rank coal first increased, then decreased as the DTAB concentration increased. The electrostatic force plays a dominant role in the adsorption of DTAB on low-rank coal surface. The adsorption of DTAB reduced the wetting heat between water and low-rank coal because the oxygen-containing groups were covered. The decrease in hydrophobicity at high DTAB concentration was due to the formation of a bilayer or micelle adsorption. MD simulation results show that the adsorption of DTAB reduced the thickness of the water adsorption layer. The nitrogen atoms of DTAB were oriented toward the coal surface, such that the alkyl chains were oriented to the water phase, thereby producing an additional repulsive effect and subsequently inhibiting the adsorption of water molecules. As a result, the number of hydrogen bonds and the interaction energy between water molecules and low-rank coal decreased, indicating that the hydrophobicity of low-rank coal was enhanced.

An investigation into surfactant flooding and alkaline-surfactant-polymer flooding for enhancing oil recovery from carbonate reservoirs: Experimental study and simulation

ABSTRACTThe main aim of the present work was to study history matching of surfactant flooding using CMG-STARS simulator and experimental results. In the experimental case, the critical micellar concentration of dodecyltrimethylammonium bromide solution is obtained, and the changes in the contact angle are investigated from 1 to 10% weight. Then, after water flooding, surfactant flooding is applied on the critical micellar concentration of dodecyltrimethylammonium bromide. In the simulation case, after history matching of production data, the performance of alkaline-surfactant-polymer flooding using sodium hydroxide, hydrolyzed polyacrylamide, and that surfactant was a prediction. The numerical simulation alkaline-surfactant-polymer flooding increased the oil recovery factor 26% more than surfactant flooding.