Cationic Surfactant Systems Research Articles

Effect of Oligomerization of Counterions on Water Activity in Aqueous Cationic Surfactant Systems

A sorption calorimetry study of cationic cetyltrimethyl ammonium surfactants with four different counterions was performed. The counterions were acetate, succinate, citrate, and butyl tetracarboxylate with formal charges ranging from 1 to 4, respectively. The counterions with 2-4 charges can be considered as oligomers. In all the cases, hydration experiments started with dry solid phases that upon water uptake went through solid-state phase transitions and hexagonal to micellar cubic phase transitions. It was found that in liquid-crystalline phases the activity of water increased with the degree of oligomerization or, equivalently, the formal charge of the counterions. The results are discussed in terms of the forces acting between the colloidal aggregates. It is argued that under the conditions investigated, the so-called strong-coupling theory can be used to describe the electrostatic forces between the charged colloidal objects. Therefore, we suggest that the observed dependence of water activity on the degree of polymerization is due to the entropy of mixing of the counterions in the water volume, which we describe using Flory-Huggins theory.

Superamphiphilic nanocontainers based on the resorcinarene – Cationic surfactant system: Synergetic self-assembling behavior

Self-organization in the mixed system based on water-soluble aminomethylated calix[4]arene with sulfonatoethyl groups at the lower rim and classical cationic surfactant cetyltrimethylammonium bromide has been studied by the methods of tensiometry, conductometry, spectrophotometry, dynamic and electrophoretic light scattering. The values of the critical association concentration, the size and zeta potential values, and the solubilization capacity of mixed aggregates toward the hydrophobic probe (Sudan I) were determined.

Perfluorinated Alcohols Induce Complex Coacervation in Mixed Surfactants.

Recently, we reported a unique and nearly ubiquitous phenomenon of inducing simple and complex coacervation in solutions of a broad variety of individual and mixed amphiphiles and over a wide range of concentrations and mole fractions. This paper describes a novel type of biphasic separation in aqueous solutions of mixed cationic-anionic (catanionic) surfactants induced by hexafluoroisopropanol (HFIP). The test cases included mixtures of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) (surfactants with different carbon chain lengths) as well as dodecyltrimethylammonium bromide (DTAB) with SDS (surfactants with the same carbon chain lengths). The CTAB-SDS-HFIP coacervate systems can be produced at many different mole ratios of surfactant, but DTAB-SDS-HFIP formed only coacervates at equimolar (1:1) mole ratios of DTAB and SDS. The phase-transition behavior of both systems was studied over a wide range of surfactant and HFIP concentrations at the stoichiometric (1:1) mole ratio of cationic/anionic surfactants. The chemical compositions of each of the two phases (aqueous-rich and coacervate phases) were studied with regard to the concentrations of HFIP, water, and individual surfactants. It is revealed that the surfactant-rich phase (coacervate phase) contains a large percentage of fluoroalcohol relative to the aqueous phase and is enriched in both surfactants but contains a small percentage of water. Surprisingly, the concentration of water in the coacervate phase increases as the total HFIP concentration is increased while the concentration of HFIP in the coacervate phase remains relatively constant, which means a larger amount of water associated with HFIP molecules is extracted into the coacervate phase, which results in the growth of the phase. The volume of the coacervate phase increases with an increase in surfactant concentration and total HFIP %. The coacervate phase is highly enriched in the two amphiphilic ions (DTA(+) and DS(-)) whereas the two counterions (Br(-) and Na(+)) primarily reside in the aqueous-rich phase. The results suggest the formation of a catanionic complex in the coacervate phase through ion pairing with a concomitant release of the surfactant counterions (Na(+) and Br(-)) into the aqueous-rich phase. Finally, the fluorocarbon alcohol systems are contrasted with the effects of aliphatic alcohols in the mixed catanionic surfactant systems. Isopropanol does not have the same interactions as HFIP with respect to solubilization, aggregation, and phase separation of the oppositely charged surfactants.

A Novel Study on the Gel Phase Formed in a Catanionic Surfactant System

AbstractA novel gel phase was constructed in a catanionic surfactant system with the compositions of 1‐tetradecyl‐3‐methylimidazolium chloride (C14mimCl) and sodium dodecyl sulfate (SDS). The gel phases were studied through visual observations, differential scanning calorimetry (DSC), rheological measurements, and scanning electron microscopy (SEM). The visual observation and DSC confirmed the formation of gels and phase transitions from gel to sol. The dynamic rheological results showed the viscoelastic properties of gels. The SEM technique was used to further indicate the microstructure of gels. Finally, the formation mechanisms of gels are proposed based on the critical packing parameter. We expect to develop a new route to construct the gels.

Thermo-responsive properties driven by hydrogen bonding in aqueous cationic gemini surfactant systems.

A series of unexpected thermo-responsive phenomena were discovered in an aqueous solution of the cationic gemini surfactant, 2-hydroxypropyl-1,3-bis(alkyldimethylammonium chloride) (n-3(OH)-n(2Cl), n = 14, 16), in the presence of an inorganic salt. The viscosity change trend for the 14-3(OH)-14(2Cl) system was investigated in the 20-40 °C temperature range. As the temperature increased, the viscosity of the solution first decreased to a minimum point corresponding to 27 °C, and then increased until a maximum was reached, after which the viscosity decreased again. In the 16-3(OH)-16(2Cl) system, the gelling temperature (T(gel)) and viscosity changes upon heating were similar to those in the 14-3(OH)-14(2Cl) system above 27 °C. The reversible conversion of elastic hydrogel to wormlike micelles in the aqueous solution of the 16-3(OH)-16(2Cl) system in the presence of an inorganic salt was observed at relatively low temperatures. Various techniques were used to study and verify the phase-transition processes in these systems, including rheological measurements, cryogenic transmission electron microscopy (cryo-TEM), electric conductivity, and differential scanning calorimetry. The abovementioned phenomena were explained by the formation and destruction of intermolecular hydrogen bonds, and the transition mechanisms of the aggregates were analyzed accordingly.

Catanionic surfactant systems—thermodynamic and structural conditions revisited

In this work, we review shortly the current state of knowledge about catanionic surfactant systems with a focus on the detailed understanding based on the molecular buildup of such systems and of the electrostatic interaction that controls their amphiphilic monolayer and bilayer. Particularly relevant here is the extent of hydrophobicity of the oppositely charged partners, which can range from just having a more or less hydrophobic counterion until a real surfactant of opposite charge. Based on this discussion, we then investigate different systems based on cetyltrimethylammonium (CTA) combined with either laurate (L) as an oppositely charged surfactant or naphthalenesulfonate (NS) as a strongly hydrophobic counterion. Both systems were studied for the case of having salt present by combining the two amphiphilic salts but also the salt-free situation which arises from combining the hydroxide with the acid. The phase behavior was determined as well as the mesoscopic structures present, as obtained by small-angle neutron scattering (SANS) and light scattering, which allow to discern formation of wormlike micelles and vesicles. Their presence was then further confirmed by rheological measurements, where in particular normal forces allow to distinguish the two types of aggregates, and control of rheology is a key property in such systems. In addition, the thermodynamic conditions in these systems were determined by means of differential scanning calorimetry (DSC). Based on these results, a consistent understanding of the formed structures and their macroscopic properties that arise from the molecular conditions in these systems is presented.

Hexafluoroisopropanol-modified cetyltrimethylammonium bromide/sodium dodecyl sulfate vesicles as a pseudostationary phase in electrokinetic chromatography

A novel catanionic surfactant vesicle system, formulated from hexafluoroisopropanol (HFIP), cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), was developed as pseudostationary phase (PSP) in electrokinetic chromatography (EKC). HFIP, as an organic modifier with the prominent properties of ionization, hydrogen bond donor and hydrophobicity, was used to effectively promote the spontaneous vesicle formation from CTAB/SDS mixed aqueous solutions, where precipitates are easy to occur due to long carbon chains, and adjust the performance of CTAB/SDS vesicles. The physical features (size and viscosity) and electrophoretic parameters (electroosmotic mobility, electrophoretic mobility and elution range) of HFIP-modified CTAB/SDS vesicles were characterized as HFIP volume content (0–4%, v/v), CTAB/SDS molar ratio (2:8–7:3mol/mol) and total surfactant concentration (10–50mM) varying, respectively. The 3% v/v HFIP-modified CTAB/SDS (3:7mol/mol, 50mM) vesicle system proves to have the largest mean diameter (288.20nm) and the widest elution range (12.41), which is also much wider than that of the corresponding other four PSP systems including trifluoroethanol (TFE)-modified CTAB/SDS vesicles (5.69), isopropanol-modified CTAB/SDS micelles (2.03), HFIP-modified SDS micelles (4.86) and unmodified SDS micelles (3.12). The chromatographic performance of the HFIP-modified vesicle system was evaluated by separating eight polycyclic aromatic hydrocarbons, nitrotoluene positional isomers, five positively charged and five negatively charged/neutral drugs, respectively. Baseline or near-baseline separation was achieved for each series of solutes. Compared with the TFE-modified vesicle system, as well as the HFIP-modified and unmodified SDS micelle systems, the HFIP-modified vesicle system shows the best separation selectivity, the highest or comparable efficiency, and the lowest retention.

The Impact of In‐situ Fabric Surface Energy on Dehydration of Fabrics

AbstractReducing liquid surface tension is widely used to increase the efficiency of the centrifugal dehydration in textile wet processing. However, increasing the dehydration efficiency by decreasing fabric surface energy is seldom studied. In this work, the impact of in situ fabric surface energy on residual moisture content (RMC) of fabrics in the dehydration processes was investigated. Different types of fluorocarbon surfactants including cationic, anionic, nonionic and amphoteric were adopted as additives in this study. The liquid surface tension and RMC were efficiently decreased when fluorocarbon surfactants were used. Notably, a cationic fluorocarbon surfactant displays similar surface tension but distinct dehydration efficiency. The in situ fabric surface energy was evaluated by measuring the n‐octane contact angle on the cotton fabric surface under the surfactant solution using the captive bubble method. It was found that the cationic fluorocarbon surfactant system gave the lowest fabric surface energy, which was probably because cationic fluorocarbon surfactants are easier to adsorb onto the surface of cotton fabric to form a fluorocarbon layer. The chemical composition (19F, 12C and 16O) analysis of the cotton fabric surface by X‐ray photoelectron spectroscopy confirms the hypothesis.

Dansyl-labeled anionic amphiphile with a hexadecanoic carbon chain: Synthesis and detection for shape transitions in organized molecular assemblies

The probing properties of a new fluorophore-labeled anionic surfactant, sodium 16-(N-dansyl)aminocetylate (16-DAN-ACA) were investigated systematically in molecular assemblies, especially in the transitions between micelles and vesicles. 16-DAN-ACA can efficiently differentiate the two different aggregate types in mixed cationic and anionic surfactant systems. The fluorescence anisotropy of 16-DAN-ACA was found to be sensitive for directly detecting the micellar growth in micelles containing oppositely charged surfactants; both cationic cetyltrimethylammonium bromide (CTAB) systems and anionic sodium dodecyl sulfate (SDS) systems were studied. The results indicated that the 16-DAN-ACA is a good fluorescent probe for differentiating the different aggregates, and even more can be used to detect the micellar growth.

Moderate the adsorption of cationic surfactant on gold surface by mixing with sparingly soluble anionic surfactant

Surfactants with amine groups are often used in the nanoparticle synthesis due to the high affinity with Au atoms. The match of charges of a capping reagent with Au has significant influence on structures in nanoparticle synthesis. Thus we studied the adsorption of a catanionic surfactant system on Au surface. The surfactants used in the study are bis[[(amidoethyl)carbamoyl]ethyl]octadecylamine (C18N3) and arachidic acid. Three combinations of the surfactants were studied with regard to the protonation state of the amine groups and the match of charges of the surfactant headgroup. The morphology of the surfactant mixtures changes from high-curvature aggregates to low-curvature with increasing the molar ratio of arachidic acid in the mixtures or the pH of the surfactant solutions. The adsorption of the mixed surfactant systems was studied by means of scanning electron microscopy (SEM), quartz crystal microbalance (QCM) and cyclic voltammetry (CV). The results revealed that the homogeneity and the compactness of the adsorbed layer on a gold surface were increased with the molar ratio of arachidic acid in the complexes. Furthermore, we may obtain the construction of the film of the mixed surfactant on gold surface using the result obtained by QCM.

Cosolubilization of 4,4′-dibromodiphenyl ether, naphthalene and pyrene mixtures in various surfactant micelles

Abstract The present study aims to investigate the cosolubilization of a range of mixtures of polybrominated diphenyl ether (PBDE) (specifically, 4,4′-dibromodiphenyl ether) and two polycyclic aromatic hydrocarbons (PAHs) (specifically, naphthalene and pyrene) in nonionic, cationic, and anionic surfactant systems. Cosolubilization effects were quantified in terms of molar solubilization ratio, micelle-water partition coefficient, and synergistic/suppressive ratio. 1 H nuclear magnetic resonance (NMR) spectroscopy was used to investigate the solubilization sites of naphthalene, pyrene, and 4,4′-dibromodiphenyl ether in surfactant micelles. During cosolubilization, synergism was observed for naphthalene/pyrene in Tween80, Brij58, CTAB, and SDBS micellar solutions due to palisade layer solubilization of naphthalene and pyrene that resulted in reduction of interfacial tension, enabling the core volume to increase. In contrast, inhibition occurred in Brij78 surfactant system due to weak interactions between PAHs and the hydrophilic chain, and competitive solubilization of PAHs for the same solubilization site. 4,4′-Dibromodiphenyl ether probably had great affinity for hydrophilic chains of surfactants due to non-covalent halogen bonding that occurred between bromines and electron donors on the hydrophilic chains, resulting in synergism for 4,4′-dibromodiphenyl ether/pyrene in all surfactant systems and resulting in inhibition for 4,4′-dibromodiphenyl ether/naphthalene in Brij58, Brij78, and CTAB surfactant systems. The results of this study provide valuable information that may improve the effective utilization of surfactants in removal of PBDEs and PAHs from contaminated soils and non-aqueous phase liquids (NAPLs) treated with surfactant enhanced remediation (SER) technology.

Aggregation behavior of Dioctadecyldimethylammonium chloride in mixed cationic surfactant system

The spontaneous formation of mixed vesicles, their coexistence and solubilization due to formation of mixed micelles were investigated for the double chain Dioctadecyldimethylammonium chloride (DODAC) and a single chain Dodecylethyldimethylammonium bromide (DDAB), mixed cationic surfactants. Various analytical techniques viz., conductivity, surface tension, fluorescence and absorption spectroscopy were utilized. To gain an insight into the mixed aggregate formed, thermodynamic free energy, molecular interaction parameter, the total critical micelle concentration and degree of ionization of the mixed micelle (α) as a function of molar ratio were assessed. Acoustic properties of the mixed surfactant system as functions of temperature were also calculated. Interaction of pyrene with mixed aggregates in the present system was assessed through fluorescence spectroscopy (at cvc as well as cmc) at 298.15K and atmospheric pressure.

Experimental and theoretical approach to mixed surfactant system of cationic gemini surfactant with nonionic surfactant in aqueous medium

The surface and mixed micellization properties of the aqueous binary mixed system of alkanediyl-α, ω-type cationic gemini surfactant, 14–4–14 and conventional nonionic surfactant, Brij-58 in an aqueous medium have been investigated over the entire mole fractions at 298.15K. The critical micelle concentration (cmc) for each mixture have been measured by tensiometric and fluorescence measurements. The solution and adsorption characteristics like composition, activity coefficients and mutual interaction parameters have been computed using different proposed theoretical models like Clint, Rosen, Rubingh, Motomura and Maeda. The strength of interaction of the surfactant is attributed to the sterical and electrical factors on mixed monolayer and micelle formation and of surfactant–surfactant interactions. The micellar aggregation number (Nagg) has also been measured using steady state fluorescence quenching method at a total concentration of ~1mM of pure components as well as their mixtures of different ratios. The micropolarity and binding constant were determined from the ratio of intensity (I1/I3) of peaks of pyrene fluorescence emission spectrum.

Mixed Cationic and Anionic Surfactant Systems Achieve Ultra-Low Interfacial Tension in the Karamay Oil Field

Based on cationic and anionic surfactant mixed systems, ultra-low interfacial tension was achieved in the Karamay oil field systems. Upon the addition of a non-ionic third component, the solubility of the mixed cationic-anionic surfactant systems increased significantly. The mixed surfactant ratio and the concentration were determined by the application in the five areas of the Karamay oil field. The interfacial tension in some real systems was found to be around 10 mN∙m-1. These cationic and anionic surfactant mixed systems have a super-resistance adsorption capacity. The results show that after 72 h of quartz adsorption, these systems can still reduce the interfacial tension to an ultra-low level.

Surface Properties of Amphiphilic Drugs in Presence of Cationic Surfactants

Surface properties of two amphiphilic drugs i.e. amitriptyline and imipramine have been studied in the absence and presence of some cationic surfactants i.e. alkyltriphenylphosphonium bromide [R = 16 (CTPB), R = 14 (TTPB)] and alkyldiethylcthanolammonium bromide [R = 16 (CDEEAB), R = 14 (TDEEAB)] by surface tension measurement at 300 K. The critical micelle concentration (CMC), maximum surface excess concentration at the air/water interface (Γ max ), minimum area per surfactant molecule at the air-water interface (A min ) and the surface pressure at the CMC (π CMC ) have been determined. Γ max value increases and CMC/π CMC decrease & with an increasing mole fraction of surfactants. The solubility of amphiphilic drugs in cationic surfactant systems has also been studied.

Behavior of Emulsification and Thickening of Crude Oil in Mixed Cationic and Anionic Surfactant Systems

We report the emulsification and thickening of crude oil using mixtures of cationic and anionic surfactants, which have high water content. The solubility of the mixed surfactants in simulated oil field water was improved by adjusting the surfactant molecular structure. The suitable concentration and mixing ratio ranges of various mixed systems were determined, and water in oil(W/O) lactescence with high water content was obtained. In addition, we studied the effects of temperature, pH value, ionic strength, and oil/water volume ratio on the emulsification and thickening processes. A series of mixed systems with good emulsification and thickening ability were determined and optimized. Notably, some of the systems increased the viscosity of the emulsion by up to 80 times. This has significance for the improvement of oil recovery.

Phase behavior and microstructures in a mixture of anionic Gemini and cationic surfactants.

We report in this work the phase behavior and microstructures in a mixture of an anionic Gemini surfactant, sodium dilauramino cystine (SDLC), and a conventional cationic surfactant, dodecyl trimethyl ammonium chloride (DTAC). Observation of the appearance shows that the phase behavior of the SDLC-DTAC mixed cationic surfactant system transforms from an isotropic homogeneous phase to an aqueous surfactant two-phase system (ASTP) and then to an anisotropic homogeneous phase with the continuous addition of DTAC. The corresponding aggregate microstructures are investigated by rheology, dynamic light scattering, transmission electron microscopy and polarization microscopy. It has been found that a wormlike micelle, in the isotropic homogeneous phase, occurs linear to the branch growth. The aggregate microstructures in the ASTP lower and upper phases are branched wormlike micelles and vesicles, respectively. The micelle transformed into a vesicle upon varying the phase volume percentage until a lamellar liquid crystal formed in the anisotropic homogeneous phase. The macroscopic phase behavior and microscopic aggregate structure are related to the understanding of the possible mechanisms for the above phenomena.

Experimental and theoretical approach to cationic drug-anionic gemini surfactant systems in aqueous medium

Herein the results of surface tension measurements on the mixed systems of an amphiphilic drug amitriptyline hydrochloride (AMT) and three anionic bisphosphodiester gemini surfactants having different hydrophobic tails (8, 10, and 12 carbon) are presented. The experimental and ideal critical micelle concentration (cmc and cmcid) values suggest synergism in mixed systems of AMT and 8-2-8/10-2-10 and attractive interaction in AMT–12-2-12 systems. Other parameters evaluated from the data also suggest mixed micellization among the components with almost 50% contribution of surfactants (micellar mole fraction, X1m, close to 0.5). The X1 values evaluated from Rubingh's model (X1m) and Motomura's model (X1M) as well as X1id values increase with increasing content of surfactants in solution. Adsorption behavior too indicates that the mixed monolayers experience attractive interaction (βσ) which vary in the order: AMT–12-2-12<AMT–8-2-8<AMT–10-2-10. Interaction in mixed micelles (βm) follows the same trend. The results suggest that mixed systems of AMT–10-2-10 are the most stable one. Probably the difference in length of hydrophobic parts of AMT and gemini is most compatible in this system.

Influence of Headgroup on the Aggregation and Interactional Behavior of Twin-Tailed Cationic Surfactants with Pluronics

The surface tension measurements have been employed to characterize the micellar and interfacial behavior of pure and mixed systems of twin-tailed cationic surfactants: dimethylene bis(decyldimethylammonium bromide) (10-2-10), didecydimethylammonium bromide (DDAB), and 1,3-didecyl-2-methylimidazolium chloride (DDIC) with pluronics P84 and F108 in the aqueous solution. The interactions of each surfactant with both pluronics are found to be nonideal and synergistic except for the mixed system of 10-2-10 + F108, for which interactions are antagonistic and every interaction has been studied on the basis of headgroup disparity. Dynamic light scattering (DLS), zeta (ζ) potential, and small angle neutron scattering (SANS) measurements have been used to determine the influence of the mixing ratio on the morphology of the various mixed aggregates that are formed. Pure DDAB is found to form unilamellar vesicles whereas pure 10-2-10 and DDIC form prolate ellipsoidal micelles. The unilamellar vesicles of DDAB are destructed to yield spherical mixed micelles on addition of pluronics via expansion or contraction of vesicles. However, the pure pluronics and their mixed systems with 10-2-10 and DDIC form charged spherical micelles, and charge is confirmed by thenfractional charge and ζ values. The ζ values of pure surfactants are found to decrease on addition of pluronics, indicating a decrease in surface charge on inclusion of pluronics.

Structural evolution of reverse vesicles from a salt-free catanionic surfactant system in toluene

A detailed study of the reverse vesicles formed by a salt-free catanionic surfactant system in toluene was carried out by confocal fluorescence microscopy observations, dye-solubilizing tests, UV–vis measurements and cryo-TEM observations. When tetradecyltrimethyl ammonium laurate (TTAL) and lauric acid (LA) were mixed in the binary solution of water and toluene, reverse vesicular phase formed spontaneously. The reverse vesicular phase is quite stable and can be labeled with fluorescent dyes for subsequent confocal fluorescence microscopy observations. However, the reverse vesicles were found to have smaller sizes (<1μm) and undergo structural evolutions in a much shorter time scale compared to those formed by the same surfactant mixture in cyclohexane, as shown in a previous report [19]. With extended observation time, interesting intermediate structures were observed including onions, sheets and cellular networks. The structural evolution pathways were deduced and the possibly influencing factors were discussed. Dye-solubilizing tests showed the ability of the reverse vesicles to accommodate dye molecules is smaller compared to those in cyclohexane. Besides, cryo-TEM observations were applied to probe the morphology of the reverse vesicles.