Mixtures Of Anionic Surfactants Research Articles

Synergistic enhancement of oil recovery: Integrating anionic-nonionic surfactant mixtures, SiO2 nanoparticles, and polymer solutions for optimized crude oil extraction

Enhanced oil recovery (EOR) methods are essential for optimizing oil extraction from modern reservoirs. This research delved into the synergistic impact of combining anionic and nonionic surfactant mixtures with silica (SiO2) nanoparticles (NPs) in sodium chloride (NaCl) solutions, alongside the added enhancement of polymers, to improve crude oil recovery. The study comprehensively evaluated stability, rheological characteristics, interfacial tension (IFT) behavior, wettability alterations, and EOR experiments using mixtures of sodium dodecyl sulfate (SDS) and triton X-100 (TX-100) surfactants. Scenarios both with and without SiO2 NPs in a base solution containing 3000 ppm NaCl and 2000 ppm xanthan gum (XG) polymer were examined. Core flooding tests were carried out on San-Saba sandstone core specimens with low permeability. The stability tests and dynamic light scattering (DLS) analysis were performed to assess the stability of NPs in low saline-surfactant-polymer solution. It was observed that NPs significantly reduced the IFT between the test solutions and crude oil, with nanofluids exhibiting satisfactory stability at a 0.4 wt% SiO2 NPs concentration. Core flooding studies demonstrated a synergistic interaction between NPs and the binary surfactant-polymer mixture, resulting in substantially greater incremental recovery of oil in comparison with the case of using binary surfactant-polymer combination alone. The mechanisms contributing to EOR with nanofluids, such as IFT reduction and wettability alteration, were explored. Incorporating NPs at concentrations of 0.1, 0.2, and 0.4 wt% led to incremental oil recoveries of 4.01 %, 12.35 %, and 12.73 % of the original oil in place (OOIP), respectively, as opposed to the recovery achieved using only SDS + TX-100 + XG. Consequently, these findings advance the understanding of the potential application of SiO2 NPs in combination with the binary surfactant-polymer mixture as effective chemical EOR agents. Additionally, these insights aid in identifying suitable sandstone reservoirs for nanofluid application, contributing to the optimization of oil recovery strategies.

Surface activity, aggregation behaviour and wettability of mixtures of perfluorobranched short-chain gemini quaternary ammonium surfactant and hydrocarbon anionic surfactants in dilute solution

The hydrophobic and oleophobic properties of perfluorobranched short chains are similar to those long chain fluorocarbons (fluorocarbon chain length ≥ 7), and their environmentally friendly properties make them good alternatives to traditional perfluorooctyl derivatives. For this purpose, a novel perfluorinated branched short chain quaternary ammonium gemini surfactant (PBFS) with high surface activity was synthesized, and the surface properties, aggregation behavior, wetting performance and adsorption performance of the complex system of PBFS and sodium octyl sulfate (SOS) were systematically studied. PBFS exhibited superior surface activity in aqueous solution with the critical micelle concentration (CMC) of 0.1667 mmol/L and the corresponding surface tension (γCMC) of 20.17 mN/m. Moreover, despite the fact that the mixing of PBFS and SOS was not ideal, the two still had the good synergistic effect: the CMC of the compounding solution was reduced to 0.0072 mmol/L and γCMC was 16.01 mN/m when the compounding ratio (CF: CH) was 1:8. And the composite solution could completely wet low surface energy polytetrafluoroethylene (PTFE) plates at 1 mmol/L, and could also wet PTFE plates at extremely low concentrations (0.0625 mmol/L), showing good wetting performance.

Finite size effects and optimization of the calculation of the surface tension in surfactant mixtures at liquid/vapour interfaces

The surface tension of monolayers with mixtures of anionic and nonionic surfactant at the liquid/vapour interface is studied. Previous works have observed that calculations of the surface tension of simple fluids show artificial oscillations for small interfacial areas, indicating that the surface tension data fluctuate due to the finite size effects and periodic boundary conditions. In the case of simulations of monolayers composed of surfactant mixtures, the surface tension not only oscillates for small areas but can also give non-physical data, such as negative values. Analysis of the monolayers with different surfactant mixtures, ionic (DTAB, CTAB, SDS) and nonionic (SB3-12), was done for density profiles, parameters of order and pair correlation functions for small and large box areas and all of them present similar behaviour. The fluctuations and the non-physical values of the surface tension are corrected when boxes with large interfacial areas are considered. The results indicate that in order to obtain reliable values of the surface tension, in computer simulations, it is important to choose not only the correct force field but also the appropriate size of the simulation box.

Interaction of sodium dodecyl sulfate and triton X-100 with ofloxacin drug using conductivity and UV–visible spectroscopic techniques in aqueous alcohols media at several temperatures

The current investigation explores the association and complexation of the mixture of anionic surfactant, sodium dodecyl sulfate (SDS), and antibiotic drug, ofloxacin (OFC) as well as nonionic surfactant, Triton X-100 (TRX) and OFC drug respectively in several additive solutions. The investigations were performed by applying conductivity and UV-Visible spectroscopic techniques. The impacts of drug concentration, types of solvents, and composition of aq. solutions of alcohols (methanol (MeOH), ethanol (EtOH), and 1-propanol (1-PrOH)) as well as temperature change have been investigated on the micelle formation of SDS + OFC mixture. The micellization of SDS + OFC and TRX + OFC systems has been characterized by the determination of critical micelle concentration (CMC) from conductivity vs. SDS concentration (conductivity technique) and Absorbance vs log[TRX] (UV-Visible spectroscopic technique) plots respectively. The micellization of SDS was delayed owing to the introduction of the OFC drug while the effect has been intensified as a function of OFC concentration. At a fixed OFC concentration and temperature, the CMC values were acquired to be augmented with the upsurge of alcohol concentration. The enhancement of the CMC changes has been perceived with the escalation of temperature at a definite concentration of OFC in water and 5% (w/w) aq. alcohols media. The disfavor of micellization of TRX in aq. EtOH solutions in comparison to aqueous solution also detected from UV-Visible spectroscopic technique. The binding constant (Kb) for the complexation of TRX with OFC drug was determined using the Benesi-Hildebrand plot. The Kb values were obtained to be affected by the change of solvent and temperature. The negative free energy change (∆Gmo/ ∆Gbo) of the micellization and complexation demonstrate the spontaneous occurrence of micelle formation and complex development. The enthalpy changes (∆Hmo) of micellization were negative (exothermic process) and entropy changes (∆Smo) were positive (highly disordered and entropy-dominated micellization). Other thermodynamic properties ((∆Hbo and ∆Sbo) and thermodynamics of transfer) have been evaluated and illustrated as well, for the working systems.

Evaluation of the effect of acid additives on rheological properties and technological efficiency of zwitterionic and anionic surfactant mixtures

Relevance. Various acid additives such corrosion inhibitors, iron stabilizers, demulsifiers, anti-precipitation agents are usually used to provide necessary technological properties to acid compositions. Adding the additives into the acid composition based on viscoelastic surfactants can have a significant impact on the efficiency of their subsequent use, since micelle formation and, consequently, rheology of their solutions are particularly sensitive to the presence of additional components in the system. Accordingly, determination of the acid additives influence on rheological properties and technological efficiency of acid compositions with surfactants is a vital task. Aim. To evaluate the effect of acid additives on rheological behavior of viscoelastic surfactants-based acid compositions (mixture of cocamidopropyl betaine and ethoxylated fatty alcohol sulfosuccinate). Object. Acidic composition based on viscoelastic surfactants (a mixture of anionic and zwitterionic surfactants) and a package of acidic additives – corrosion inhibitor, iron stabilizer, demulsifier and antisludge agent. Methods. Investigation of rheological properties using an MCR52 rheometer (Anton Paar GmBH) in the shear rate range from 1 to 100 s–1 at temperatures from 20 to 90°C, standard tests for selecting acid additives. Results. The authors have determined the effect of acid additives on rheological properties of the developed self-diverting acid solution based on the viscoelastic surfactant (a mixture of anionic and zwitterionic surfactants). The obtained results confirmed that adding the acid additives into solutions leads to a decrease in partially neutralized solution viscosity. However, it expands the range of manifestation of viscoelastic properties. This will increase the efficiency of the developed composition during acid treatment. Also, the addition of acid additives reduces the initial viscosity, which facilitates acid injection into formation. A viscoelastic gel is not formed with hydrocarbons, which indicates that the treatment is effective in cleaning up the area after acidizing. The temperature test showed that the additives do not affect the temperature range of acid solution application.

Impact of lipid matrix composition on the activity of membranotropic enzymes galactonolactone oxidase from Trypanosoma cruzi and L-galactono-1,4-lactone dehydrogenase from <i>Arabidopsis thaliana</i> in the system of reverse micelles

The study of many membrane enzymes in an aqueous medium is difficult due to the loss of their catalytic activity, which makes it necessary to use membrane-like systems, such as reverse micelles of surfactants in nonpolar organic solvents. However, it should be taken into account that micelles are a simplified model of natural membranes, since membranes contain many different components, a significant part of which are phospholipids. In this work, we studied the impact of the main phospholipids, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), on the activity of membrane enzymes using galactonolactone oxidase from Trypanosoma cruzi (TcGAL) and L-galactono-1,4-lactone dehydrogenase from Arabidopsis thaliana (AtGALDH) as an examples. Effect of the structure (and charge) of the micelle-forming surfactant itself on the activity of both enzymes has been studied using an anionic surfactant (AOT), a neutral surfactant (Bridge-96), and a mixture of cationic and anionic surfactants (CTAB and AOT) as an examples. The pronounced effect of addition of PC and PE lipids on the activity of AtGALDH and TcGAL has been detected, which manifests as increase in catalytic activity and significant change in the activity profile. This can be explained by formation of the tetrameric form of enzymes and/or protein-lipid complexes. By varying composition and structure of the micelle-forming surfactants (AOT, CTAB, and Brijdge-96 and their combinations) it has been possible to change catalytic properties of the enzyme due to effect of the surfactant on the micelle size, lipid mobility, charge, and rigidity of the matrix itself.

Aqueous two-phase system based on benzethonium chloride and sodium dihexyl sulfosuccinate for extraction and ICP-OES determination of heavy metals

An aqueous two-phase system (ATPS) based on benzethonium chloride (BztCl) and sodium dihexyl sulfosuccinate (NaDHSS) was proposed for the first time for liquid-liquid microextraction of Cd(II), Co(II), Cu(II), Mn(II), Ni(II), and Pb(II) followed by ICP-OES determination. The mixture of cationic and anionic surfactants, BztCl and NaDHSS, showed liquid-liquid phase separation at the molar ratio of 1:1, and the total surfactant concentration of 0.01–0.2 mol L−1 forming ATPS that was investigated in the extraction process. The extraction efficiency for Cd(II), Co(II), Mn(II), Ni(II), and Pb(II) was nearly 100 %, and for Cu(II) – not lower than 88 % in the presence of 8-hydroxyquinoline as a complexing agent. The surfactant-rich phase containing analytes was subjected to back-extraction with 0.2 M HNO3 before ICP-OES measurements. The preconcentration in the proposed BztCl–NaDHSS–H2O ATPS for 30 s and the high degree of back-extraction, which was achieved in 1 min, significantly reduced the sample preparation time, matrix effects and provided low LODs in the range of 0.04–1.0 μg L−1, the preconcentration factor was 120. The analysis of a certified reference material sample of surface water and the real samples of tap, sea, and waste water verified the method accuracy.

Impact of Lipid Matrix Composition on Activity of Membranotropic Enzymes Galactonolactone Oxidase from Trypanosoma cruzi and L-Galactono-1,4-Lactone Dehydrogenase from Arabidopsis thaliana in the System of Reverse Micelles.

The study of many membrane enzymes in an aqueous medium is difficult due to the loss of their catalytic activity, which makes it necessary to use membrane-like systems, such as reverse micelles of surfactants in nonpolar organic solvents. However, it should be taken into account that the micelles are a simplified model of natural membranes, since membranes contain many different components, a significant part of which are phospholipids. In this work, we studied impact of the main phospholipids, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), on activity of the membrane enzymes using galactonolactone oxidase from Trypanosoma cruzi (TcGAL) and L-galactono-1,4-lactone dehydrogenase from Arabidopsis thaliana (AtGALDH) as examples. Effect of the structure (and charge) of the micelle-forming surfactant itself on the activity of both enzymes has been studied using an anionic surfactant (AOT), a neutral surfactant (Brij-96), and a mixture of cationic and anionic surfactants (CTAB and AOT) as examples. The pronounced effect of addition of PC and PE lipids on the activity of AtGALDH and TcGAL has been detected, which manifests as increase in catalytic activity and significant change in the activity profile. This can be explained by formation of the tetrameric form of enzymes and/or protein-lipid complexes. By varying composition and structure of the micelle-forming surfactants (AOT, CTAB, and Brij-96) it has been possible to change catalytic properties of the enzyme due to effect of the surfactant on the micelle size, lipid mobility, charge, and rigidity of the matrix itself.

Towards compartmentalized micelles: Mixed perfluorinated and hydrogenated ionic surfactants in aqueous solution

HypothesisAqueous solutions of mixtures of hydrogenated and perfluorinated ionic surfactants are known to display anomalous aggregation behavior due to the mutual phobicity between hydrogenated and perfluorinated chains. Despite all efforts, different experimental limitations prevented so far a definite interpretation of the existing experimental results: both intermicellar and intramicellar segregation remain acceptable possibilities. MethodThe potential for segregation of mixtures of fluorinated and hydrogenated ionic surfactants in water was assessed using atomistic molecular dynamics simulations. Aqueous mixtures of hydrogenated and perfluorinated ionic surfactants were studied: mixtures of anionic surfactants (sodium dodecylsulfate (SDS) + sodium perfluoro-octanoate (SPFO)) and catanionic surfactants (decyltrimethylammonium bromide (DeTAB) + SPFO) were simulated. FindingsThe mixture of anionic surfactants, SDS + SPFO, exhibits clear intramicellar segregation between fluorinated and hydrogenated chains, displaying hydrogenous-rich and fluorous-rich regions. Compartmentalized micelles are thus clearly formed. The simulation results also suggest the possibility of intermicellar segregation. Conversely, catanionic mixtures of DeTAB and SPFO in water solution assemble into a large oblate structure, containing all available molecules in the simulation box, resembling a double layer membrane or a vesicle wall. In this case mixing between fluorinated and hydrogenated surfactants is dictated by charge alternation.

SLE3S-water system: a linear rheological characterisation

AbstractSurfactant-water mixtures display a complex rheological behaviour, with changes in parameters such as viscosity and moduli of several orders of magnitude as a consequence of phase changes, depending on their concentration and temperature: this criticism heavily affects different industrial processes. In our work, linear rheological behaviour of aqueous mixtures of a commercial anionic surfactant, sodium lauryl ether sulphate, is investigated in a range of temperature (30–60 °C) and surfactant concentration (20–72%wt) of technological relevance. Four phases with different texture are identified by polarised light microscopy: micellar, hexagonal, cubic and lamellar, all showing a shear-thinning behaviour. Rheological parameters of cubic phase show a net jump in a relatively narrow temperature range, suggesting a temperature-induced phase change. The systematic analysis of the rheological behaviour of this widely used surfactant system, reported here for the first time, can be of fundamental support for many industrial applications. Graphical Abstract

Continuous Electrophoretic Separation of Charged Dyes in Liquid Foam

A novel electrophoretic separation technique is presented, where continuous electrophoretic separation is demonstrated using free flowing liquid foams. Continuous foam electrophoresis combines the principle of capillary electrophoresis and interactions between analytes and the electrical double layer, with the ability of Free Flow Electrophoresis to continuously separate and recover analytes automatically. A liquid foam is used to provide a network of deformable micro and nano channels with a high surface area, presenting a novel platform for electrophoresis, where interfacial phenomena could be exploited to modify analyte migration. The main purpose of this paper is to present a proof-of-concept study and provide fundamental understanding of a complex foam system in continuous separation mode, i.e., flowing liquid foam under an external electric field with electrophoresis and chemical reactions at the electrodes continuously changing the system. Liquid foam is generated using a mixture of anionic and non-ionic surfactants and pumped through a microfluidic separation chamber between two electrodes. The effectiveness of the device is demonstrated using a dye mixture containing a neutral dye and an anionic dye. At the outlet, the foam is separated and collected into five fractions which are individually probed for the concentration of the two dyes used. The anionic dye was concentrated up to 1.75 (±0.05) times the initial concentration in a select outlet, while the neutral dye concentration remained unchanged in all outlets, demonstrating the potential for electrophoretic foam separations.

Synergistic effect of binary mixture of anionic nonionic surfactant on inhibiting coal dust pollution: Experiment and simulation

Coal dust is a pollutant particle generated during the process of coal development and utilization. It can cause damage to the surrounding environment and human health. In this paper, experimental and molecular dynamics simulations were used to select four surfactants: fatty alcohol polyoxyethylene ether sodium sulfate (AES), sodium dodecyl benzene sulfonate (SDBS), lauryl glucoside (APG-12), and fatty alcohol polyoxyethylene ether (AEO-9). The wettability and adsorption ability of a single surfactant and a combination of surfactants were studied at the macro and micro levels, Laying a foundation for the preparation of binary surfactants. The results show that the anionic nonionic binary composite aqueous solution of 0.07% SDBS and 0.05% AEO-9 can greatly increase the content of hydrophilic functional groups in coal molecules, and its hydrophobic groups can be firmly adsorbed on the pore size of coal dust, effectively solving the problem of poor hydrophilicity and difficult wetting of coal dust. In addition, on the basis of quantitative characterization of micromolecules and macro wetting test, research on foam characteristics has been added to further improve dust suppression efficiency and effectively control air pollution caused by coal mining and use.

Mitigating the skin irritation potential of mixtures of anionic and non-ionic surfactants by incorporating low-toxicity silica nanoparticles

There has been a notable upswing in the adoption of product formulations based on nanotechnology within the cosmetics industry. By using nanocarriers, such as solid or micellar nanoparticles, the quality and performance of cosmetics can be improved, allowing for better transport of bioactive components into the skin. However, it is important to note that the interaction between these compounds may lead to skin irritation. To mitigate skin irritability, nano-formulation strategies should be implemented in cosmetics. A proof-of-concept study was therefore conducted to investigate if low-toxicity nanoparticles (silica) could be used in combination with a mixture of anionic surfactants and a low-irritant cosurfactant (non-ionic) to develop safer cosmetic formulations that reduce skin damage. The skin irritation potential of the formulations was assessed in vitro using the well-known Zein method.As anticipated, non-ionic surfactants pose the lowest risk for skin irritation. When compared to single anionic surfactants, non-ionic/anionic mixtures were found to decrease skin irritability by 24–67 %. However, when silica nanoparticles (NPs) were added to single surfactants, the potential for skin irritation increased, particularly when the anionic surfactant molecules were arranged in a spherical core-shell structure around the surface of the NPs. On the other hand, incorporating NPs in surfactant mixtures enhanced their formulation stability. While all three-component formulations were found to decrease skin irritability, those that formed spherical core-shell structures demonstrated the most significant reduction, likely related to a reduction in charge density caused by the non-ionic surfactant which may decrease protein solubilisation. Therefore, the inclusion of silica NPs can potentially result in a further reduction of the skin irritation potential caused by mixtures of anionic and non-ionic surfactants.

Inhibitive effect of anionic/zwitterionic hybrid surfactants on the self-corrosion of anode for alkaline Al-air battery

Surfactants have been increasingly used as corrosion inhibitors in recent years. The zwitterionic surfactants can keep their amphoteric characteristics within a wide range of pH and temperature. In this research work，the self-corrosion of Al anode in alkaline electrolyte for Al-air battery is suppressed by adding a hybrid corrosion inhibitor consisting of dodecyl dimethyl betaine (DDBT) and sodium dodecylbenzene sulfonate (SDBS). The hybrid surfactant behaves as an anodic inhibitor. The results show that the optimum inhibition efficiency is 91.27 % for 1 × 10−3 M DDBT + 4 × 10−3 M SDBS. The combination of DDBT and SDBS decreases the corrosion rate of AA5052 alloy in sodium hydroxide electrolyte. The hydrophilic heads of DDBT and SDBS can adsorb on surface. The long alkyl chains in surfactant bring an increase in hydrophobicity. The hybrid surfactants have the electrostatic interaction and hydrophobic interaction, which improving the inhibition effect for the hydrogen evolution reaction. In general, the mixture of anionic and zwitterionic surfactants can provide the potential for better inhibition performance and significance for practical application.

Wormlike Micelles with Photo and pH Dual-Stimuli-Responsive Behaviors Formed by Aqueous Mixture of Cationic and Anionic Surfactants

Responsive wormlike micelles, innovative soft materials with stimuli-tunable rheological properties, have recently attracted significant attention. Herein, the construction of dual responsive wormlike micelles exhibiting photo- and pH-stimulated viscoelastic behaviors is demonstrated from a cationic surfactant 4,4′-bis(trimethylammonium-6-hexyloxy) azobenzene bromide (BTHA), and anionic surfactant sodium oleate (NaOA). Rheological measurement, dynamic light scattering, and cryogenic transmission electron microscopy were used to explore the dual-responsive behaviors of wormlike micelles system systematically. The results show that the self-assembly structures and viscoelastic behaviors of the mixed system can be regulated by light irradiation and pH. With BTHA concentration ≥ 20 mM, the mixed solutions show a shear-thinning behavior, implying the formation of wormlike micelles. Under UV light irradiation at 365 nm, the photoisomerization of BTHA from trans to cis affects the molecular packing at micellar interface, that leads to the aggregate structures transformation from wormlike micelles into spherical micelles, accompanied by an apparent decrease in zero-shear viscosity of the mixed solution by three orders of magnitude. The transformation is reversible in the presence of Vis light (420 nm). Moreover, the pH-responsive behavior could also be reversibly switched by adding HCl or NaOH, due to the protonation of NaOA molecules. The interconversion of gel-like solution and water-like fluid could occur by adjusting pH values between 10.26 and 8.95, which reflect variations in microstructures and was ascertained the transformation between wormlike micelles and spherical micelles by cryo-TEM. The relationship of temperature and the structural relaxation time (τR) follows the Arrhenius law, resulting from the decreasing micellar contour length. This work will enhance our understanding of the multi-responsiveness of intelligent materials and hold great promising applications in biomedicine, oil industry, smart molecular device, and sensors.

Highly-Selective Harvesting of (6,4) SWCNTs Using the Aqueous Two-Phase Extraction Method and Nonionic Surfactants.

Monochiral single-walled carbon nanotubes (SWCNTs) are indispensable for advancing the technology readiness level of nanocarbon-based concepts. In recent times, many separation techniques have been developed to obtain specific SWCNTs from raw unsorted materials to catalyze the development in this area. This work presents how the aqueous two-phase extraction (ATPE) method can be enhanced for the straightforward isolation of (6,4) SWCNTs in one step. Introducing nonionic surfactant into the typically employed mixture of anionic surfactants, which drive the partitioning, is essential to increasing the ATPE system's resolution. A thorough analysis of the parameter space by experiments and modeling reveals the underlying interactions between SWCNTs, surfactants, and phase-forming agents, which drive the partitioning. Based on new insight gained on this front, a separation mechanism is proposed. Notably, the developed method is highly robust, which is proven by isolating (6,4) SWCNTs from several raw SWCNT materials, including SWCNT waste generated over the years in the laboratory.

Structural changes of viscoelastic solutions of zwitterionic and anionic surfactant mixtures under the influence of simple salt

Structural changes of viscoelastic solutions of zwitterionic and anionic surfactant mixtures under the influence of simple salt

Model Catanionic Vesicles from Biomimetic Serine-Based Surfactants: Effect of the Combination of Chain Lengths on Vesicle Properties and Vesicle-to-Micelle Transition

Mixtures of cationic and anionic surfactants often originate bilayer structures, such as vesicles and lamellar liquid crystals, that can be explored as model membranes for fundamental studies or as drug and gene nanocarriers. Here, we investigated the aggregation properties of two catanionic mixtures containing biomimetic surfactants derived from serine. The mixtures are designated as 12Ser/8-8Ser and 14Ser/10-10Ser, where mSer is a cationic, single-chained surfactant and n-nSer is an anionic, double-chained one (m and n being the C atoms in the alkyl chains). Our goal was to investigate the effects of total chain length and chain length asymmetry of the catanionic pair on the formation of catanionic vesicles, the vesicle properties and the vesicle/micelle transitions. Ocular observations, surface tension measurements, video-enhanced light microscopy, cryogenic scanning electron microscopy, dynamic and electrophoretic light scattering were used to monitor the self-assembly process and the aggregate properties. Catanionic vesicles were indeed found in both systems for molar fractions of cationic surfactant ≥0.40, always possessing positive zeta potentials (ζ = +35-50 mV), even for equimolar sample compositions. Furthermore, the 14Ser/10-10Ser vesicles were only found as single aggregates (i.e., without coexisting micelles) in a very narrow compositional range and as a bimodal population (average diameters of 80 and 300 nm). In contrast, the 12Ser/8-8Ser vesicles were found for a wider sample compositional range and as unimodal or bimodal populations, depending on the mixing ratio. The aggregate size, pH and zeta potential of the mixtures were further investigated. The unimodal 12Ser/8-8Ser vesicles (<DH> ≈ 250 nm, pH ≈ 7-8, ζ ≈ +32 mV and a cationic/anionic molar ratio of ≈2:1) are particularly promising for application as drug/gene nanocarriers. Both chain length asymmetry and total length play a key role in the aggregation features of the two systems. Molecular insights are provided by the main findings.

When Bulk Matters: Disentanglement of the Role of Polyelectrolyte/Surfactant Complexes at Surfaces and in the Bulk of Foam Films

Foam films display exciting systems as on one hand they dictate the performance of macroscopic foams and on the other hand they allow studies of surface forces. With regard to surface forces, we attempt to disentangle the effect of the foam film surfaces and the foam film bulk. For that, we study the influence of salt (LiBr) on foam films formed by mixtures of oppositely charged polyelectrolyte and surfactant: anionic monosulfonated polyphenylene sulfone (sPSO2-220) and cationic tetradecyltrimethylammonium bromide (C14TAB). Adding a small amount of salt (≤10-3 M) decreases the foam film stability due to a weakened electrostatic net repulsion. In contrast, a large amount of salt (10-2 M) unexpectedly increases the foam film stability. Disjoining pressure isotherms reveal that the increased stability is due to an additional steric stabilization, which is attributed to sPSO2-220/C14TAB complexes in the film bulk. These bulk complexes also contribute to the measured apparent surface potential between the two air/water interfaces. We find, for the first time, the formation of Newton black films for mixtures of anionic polyelectrolytes and cationic surfactants.

Alkylether derivatives of choline as cationic surfactants for the design of soluble catanionic systems at ambient conditions

Mixtures of cationic and anionic surfactants are promising systems with great potential for various purposes in surface and interfacial science. However, so far their applicability has been severely limited by poor solubility at and around equimolar ratios, where too strong interactions typically cause precipitation. In the present study, we hypothesized that the insertion of ethylene oxide units between hydrophobic alkyl chains and a positively charged choline headgroup should give cationic surfactants with high intrinsic flexibility, hindering phase separation and thus allowing soluble catanionic mixtures to be formed at room temperature with conventional sulfate-based anionic surfactants. To that end, different alkylether derivatives of choline were synthesized and combined with alkyl or alkylether sulfates at varying ratios in water. The resulting mixtures of cationic and anionic surfactants were characterized in detail with respect to solubility, static and dynamic activity at surfaces and liquid/oil interfaces, adsorption on solid substrates, and cytotoxicity. In further application-oriented tests, the potential of the developed catanionic surfactant systems for wetting of hydrophobic surfaces, stabilization of liquid foams, and stain removal in lab-scale washing experiments was assessed. Our results demonstrate that the synthesized cationic surfactants can be combined with conventional anionic surfactants to give water-soluble systems across the entire range of mixing ratios, including equimolarity. This remarkable enhancement of solubility is found to be accompanied by pronounced synergistic effects in terms of interfacial activity, evidenced among others by low surface tensions, strong adsorption on solid interfaces as well as fast and complete spreading on hydrophobic substrates. These promising, and readily tunable, physicochemical properties are also reflected in improved foaming and cleaning performance, highlighting the potential of soluble catanionic surfactant formulations for a broad range of industrially relevant applications.