Mixtures Of Cationic Surfactants Research Articles

Self-assembly of surfactant mixtures for a versatile control of the rate of the heterogeneous reaction: Case study in Cu electrodeposition

This study introduces surfactant mixtures as versatile controllers for the rate of heterogeneous reactions. Contrary to the use of a single surfactant, a mixture of cationic surfactant and anionic surfactant allows for a more diverse change on the rate of Cu electrodeposition as a typical example of a heterogeneous reaction. Dodecyltrimethylammonium bisulfate (DTABS) as a cationic surfactant suppresses the rate via adsorption on the reaction surface whereas sodium dodecyl sulfate (SDS) anionic surfactant exhibits a weak enhancement. Small-angle X-ray scattering analyses identify various types of surfactant assemblies present in the electrolyte containing DTABS and SDS. Their formation was associated with the change in the rate: the addition of SDS enhances the suppressing effect of DTABS in DTABS-rich mixed micelle phase; however, further addition of SDS neutralizes this effect with the formation of precipitates, vesicles, and SDS-rich micelles. The corresponding changes in the coverage of the surfactant adsorbates on the reaction surface are analyzed electrochemically. The ability of DTABS-SDS mixture can be utilized for Cu electrodeposition on a patterned structure, and it realizes the effective deep via fill. To the best of our knowledge, this is the first demonstration of controlling the rate of heterogeneous reactions using surfactant mixtures.

Impact of the Hydrophobic Phase on the Interfacial Dilational Rheology of Alkoxy Carboxylate/Cetyltrimethyl Ammonium Chloride Mixtures.

Despite extensive investigations on the interfacial activities of mixed anionic and cationic surfactants (Sa/c), the influence of the hydrophobic phase on their interfacial assembly and dilational rheology remains unaddressed. In this study, the interfacial dilational rheology of alkoxy carboxylate (anionic)/cetyltrimethylammonium chloride (cationic) surfactant mixtures was studied at various interfaces. The dilational modulus of Sa/c increases linearly with interfacial pressure at the interfaces of air, n-hexane/n-octane/n-hexadecane, and toluene. The limit elasticity (ε0) is similar at air and alkane interfaces but significantly decreases at the toluene interface. To explain these phenomena, all-atom molecular simulation was carried out to investigate the microscopic features of surfactants at the interface. The findings emphasize the crucial role of anionic/cationic surfactant bound pairs in regulating interfacial rheology. Sa/c tend to form large aggregates at the air/water surface. When mixed with alkanes like octane, most Sa/c remain as ion pairs. However, when toluene is employed, the coordination number between anionic and cationic surfactants sharply decreases due to π-π interactions between the toluene molecules and the phenyl groups in the anionic surfactant. This leads to a much lower interfacial modulus because interactions between oil molecules and surfactants cannot compensate for weakened interactions among anionic/cationic surfactants. These results suggest that Sa/c in this study tolerate alkanes but are not resistant to aromatics, which helps explain why Sa/c demonstrate excellent performance for the chemical enhanced oil recovery of a high-wax reservoir and further provides fundamental knowledge of their potential applications, such as gas well deliquification using foamers in the presence of condensate oil, textiles, etc.

The aggregation structure and rheological properties of catanionic surfactant mixtures and potential applications in fracturing fluids

Clean fracturing fluids are widely used in reservoir stimulation and increasing production due to their characteristics of simple preparation, no residue, easy flowback, and low damage. At present, clean fracturing fluids are mainly prepared by cationic surfactants as main agent and inorganic or organic salts as additives, which can lead to unavoidable losses of cationic surfactants due to their adsorption in the formation. Anionic-cationic surfactants composite system can not only compensate for the shortcomings of a single surfactant system, but also improve the reservoir adaptability of the surfactant system. In this paper, a clean fracturing fluid was prepared with long-chain anionic surfactant, Sodium erucate (NaOEr), as main agent and a series of cationic surfactants with different as additive. Then, the aggregation behavior of mixed system was determined by visual appearance, rheology experiments, differential scanning calorimetry and cryogenic transmission electron microscopy. The phase transition mechanism induced by temperature was proposed, and the performance of the mixed system as a fracturing fluid was evaluated. The results showed the mixed systems could self-assemble into wormlike micelles when the length of hydrophobic carbon chains of cationic surfactant was 6 and 8. Increasing the length of the hydrophobic carbon chain could enhance the electrostatic effect, leading to precipitation in the mixed system. When the ratio of cationic surfactant was between 0.5 and 0.6 and the concentration was between 68 and 175 mmol∙L-1, the mixed systems tended to form three-dimensional structures by entangling and stacking wormlike micelles, showing high viscoelasticity and viscosity. The aggregation structure of the mixed system transformed from vesicles to wormlike micelles at 46.8 °C, which is attributed to the transition of carbon chains of NaOEr from non-flexible to flexible. Finally, the mixed system as a fracturing fluid has good shear resistance and temperature resistance. The viscosity of NaOEr/HTAB can reach above 50 mPa⋅s after sheared for 60 min at the conditions of 170 s−1 and 80 °C. This study provides an anionic clean fracturing fluid and broaden the application of viscoelastic surfactants in oilfield development.

A Study on the Effect of New Surfactant Proportions on the Recovery Improvement of Carbonate Reservoir

The strategy of integrating water injection and chemical additives in combining secondary and tertiary oil recovery techniques has been widely investigated in enhancing oil recovery efficiency. Nevertheless, there is a lack of sufficient evidence on the effectiveness of a mixture of cationic and nonionic surfactants combined with water injection techniques in enhancing recovery in the application of carbonate reservoirs. Therefore, it is particularly critical to explore the impact of this combination strategy in enhancing recovery in fractured carbonate reservoirs. The recovery enhancement effect can be assessed by conducting phase behavior experiments and determining interfacial tension and contact angle. Further, the effectiveness of specific surfactant ration solutions in enhancing recovery can be verified by performing drive-off experiments. The results show that low mineralization water and surfactants have a significant synergistic effect in enhancing the recovery efficiency of carbonate reservoirs, with the optimal ratio of cationic to non-ionic surfactants being 2.5:1. The optimized surfactant ratio is able to increase the recovery of carbonate reservoirs by 20% compared to the original recovery rate.

Interaction, Surface Activity, and Application of Mixed Systems of Alcohol Ether Sulfate Anionic Surfactants with Multiple Ethylene Oxide Groups and Gemini Quaternary Ammonium Surfactant.

The surface activities and application properties for the mixtures of cationic surfactants tetramethylene-1,4-bis[N,N-bis(hydroxypropyl)-hexa/decyloxypropylammonium] bromide (GC10-P) and tetramethylene-1,4-bis[N,N-bis(hydroxyethyl)-hexa/decyloxypropylammonium] bromide (GC10-E) and anionic surfactant isomeric sodium fatty alcohol ether sulfates (iso-AE9S) were investigated using both the tensiometry and the conductometry. The interaction parameters and thermodynamic micellization parameters of GC10-P/iso-AE9S and GC10-E/iso-AE9S mixtures were evaluated by Clint-Rubingh and Motomura theoretical models. When the mole fraction of α1 for GC10-P/iso-AE9S mixed system was 0.2, the critical micelle concentration (CMC) reached a minimum of 1.61 × 10-4 mol/L, and the minimum critical micelle concentration of the GC10-E/iso-AE9S mixed system is 2.67 × 10-5 mol/L at α1 = 0.6. The CMC value of the mixed system is 1-2 orders of magnitude lower than that of any single component. The results indicate that the synergistic effects of the investigated mixed systems (evaluated by βm) are in order of GC10-P/iso-AE9S < GC10-E/iso-AE9S, with maximum βm values of -17.98 and -9.78, respectively. The change in zeta potential indicates that the poly(ethylene oxide) chain has weakened the charge density of the hydrophilic headgroup of the anionic surfactant. The interfacial tension at the oil-water interface in the mixed system of anionic/cationic surfactants is lower than that of any single component, exhibiting a higher interfacial activity. The mixed system exhibits a decreased contact angle and superior wetting ability over any single component, and it also enhances foam performance, emulsification performance, and degreasing performance.

Impact of lipid matrix composition on the activity of membranotropic enzymes galactonolactone oxidase from Trypanosoma cruzi and L-galactono-1,4-lactone dehydrogenase from &lt;i&gt;Arabidopsis thaliana&lt;/i&gt; 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.

Cationic-anionic surfactant mixtures based on gemini surfactant as a candidate for enhanced oil recovery

The surface and interfacial properties of bisquaternary ammonium salts (16−4−16), sodium dodecyl benzene sulfonate (SDBS), and their mixture were investigated. Moreover, the effects of adsorption on the crude oil/water interfacial tension (IFT) of the SDBS/16–4–16 mixture were examined. Finally, the wettability alternation, oil film peeling-off performance, and core flooding were used to evaluate the enhanced oil recovery of the SDBS/16–4–16 mixture. Results show that the cationic Gemini surfactant 16–4–16 exhibits a strong synergistic effect with SDBS in surface/interfacial activity. At αSDBS = 0.66, the CMC value of the SDBS/16–4–16 mixtures reaches the lowest (0.016 mmol/L), and the interaction parameter (βm) exhibits a minimal value (−11.47), indicating a strong attraction between the cationic and anionic surfactants. When αSDBS is between 0.2 and 0.7, the diesel/water IFT is reduced below 10−2 mN/m, and the IFT shows little relationship with the mixing ratio. For crude oil, when αSDBS is equal to 0.4 and 0.5, the SDBS/16–4–16 mixtures can also reduce the crude oil/water IFT to ultra-low (<10−2 mN/m). When the mineralization is between 5000 mg/L and 20,000 mg/L, the IFT of crude oil/water can be reduced to 3.3 × 10−3 mN/m.Adsorption time, temperature, and liquid-solid ratio have less effect on the IFT of the SDBS/16–4–16 mixture (αSDBS = 0.4) than cationic surfactant 16–4–16. As static adsorption time increases to 24 h, the IFT of the SDBS/16–4–16 mixture only increases from 3.13 × 10−3 mN/m to 4.58 × 10−3 mN/m, while 16–4–16 increases the IFT from 0.121 mN/m to 0.202 mN/m. Furthermore, the SDBS/16–4–16 mixture takes only 10 min to reach dynamic adsorption equilibrium, shorter than the two pure components. The ability of the SDBS/16–4–16 mixtures to reduce the contact angle on the lipophilic glass surface and the oil film peeling-off performance is significantly superior to 16–4–16 and SDBS. As low as 0.1 mmol/L, the SDBS/16–4–16 mixture (αSDBS = 0.4) can reduce the contact angle of oil-wet glass surface from 107° to 46°, while 16–4–16 reduces it to 68° and SDBS to 79°. Eventually, the SDBS/16–4–16 mixture (αSDBS = 0.4) shows excellent performance in the core flooding experiments. The SDBS/16–4–16 mixture could improve crude oil recovery by 26.2%, demonstrating great potential in EOR.

Dilution-Induced Deposition of Concentrated Binary Mixtures of Cationic Polysaccharides and Surfactants.

This work investigates the effect of dilution on the phase separation process of binary charged polysaccharide-surfactant mixtures formed by two cationic polysaccharides and up to four surfactants of different nature (anionic, zwitterionic, and neutral), as well as the potential impact of dilution-induced phase separation on the formation of conditioning deposits on charged surfaces, mimicking the negative charge and wettability of damaged hair fibers. The results obtained showed that the dilution behavior of model washing formulations (concentrated polysaccharide-surfactant mixtures) cannot be described in terms of a classical complex precipitation framework, as phase separation phenomena occur even when the aggregates are far from the equilibrium phase separation composition. Therefore, dilution-enhanced deposition cannot be predicted in terms of the worsening of colloidal stability due to the charge neutralization phenomena, as common phase separation and, hence, enhanced deposition occurs even for highly charged complexes.

Synergism and molecular mismatch in rhamnolipid/CTAC catanionic surfactant mixtures

Rhamnolipids represent a promising class of biosurfactants, whose industrial exploitation could potentially reduce the ecological impact of surfactant-based formulations. In this direction, the rational design of rhamnolipid mixtures with other surfactants constitutes a strategic field of research.In this work, we combine mono-rhamnolipid (mRha) with the cationic surfactant cetyltrimethylammonium chloride (CTAC). The study is conducted at pH = 7.1, so that the mRha carboxylic group is dissociated and catanionic mRha-CTAC mixtures form. The system is investigated across the entire composition range by surface tension and conductivity measurements, which show a strong synergism between the two surfactants in forming mixed aggregates, specifically in mRha-rich mixtures. No coacervation or precipitation is observed, due to the strong asymmetry between the surfactant molecular architectures, with mRha presenting a bulky headgroup and two relatively short tails compared to the single long tail of CTAC. Dynamic Light Scattering (DLS) and Small Angle Neutron Scattering (SANS) experiments show that, while the single surfactants predominantly form small micelles, their mixing results in the spontaneous formation of vesicles. Within the vesicle bilayer, the termini of the longer surfactant tails fold, assuming disordered conformations, as probed by Electron Paramagnetic Resonance (EPR) measurements.These results point to the rational design of rhamnolipid-based catanionic mixtures as a suitable tool to optimize their structural properties, constituting a solid basis for their practical applications.

Adsorption mechanism of HTAB-octanol mixture onto silica sensor by QCM-D and MD simulation

Adsorption of a mixture of cationic surfactant, Hexadecyl Trimetehyleammonium Bromide (HTAB) and octanol on silica surface has been studied at various surfactant and octanol concentrations by QCM-D (Quartz Crystal Microbalance with Dissipation monitoring) and Molecular Dynamics (MD) simulations. In the QCM-D studies, frequency, and dissipation values with HTAB alone gradually and significantly increased from −2 to −18 Hz and 0.18 × 10−6 to 1.2 × 10−6, respectively. However, addition of octanol to HTAB was shown to achieve better adsorption properties due to the co-adsorption effect. The frequency values with increasing octanol concentrations at constant HTAB concentration of 5 × 10−4 M raised them to −10 to −20 Hz with the favorable help of hydrophobic forces. Dissipation values, on the other hand, were significantly improved in the presence of alcohol due to chain length contribution. In addition, increase in contact angle values with increasing octanol concentration at constant HTAB concentration supports the QCM-D results. Experimental studies were then corroborated by Molecular Dynamics (MD) simulations to clarify morphological and structural properties of surfactant in the presence and absence of octanol. MD simulations demonstrated that interaction of HTAB with the silica surface is much more conducive due to the presence of octanol in the medium.

Thermodynamics and Viscoelastic Property of Interface Unravel Combined Functions of Cationic Surfactant and Aromatic Alcohol against Gram-Negative Bacteria.

Lipopolysaccharides (LPSs), the major constituents of the outer membranes of Gram-negative bacteria, play a key role in protecting bacteria against antibiotics and antibacterial agents. In this study, we investigated how a mixture of cationic surfactants and aromatic alcohols, the base materials of widely used sanitizers, synergistically act on LPSs purified from Escherichia coli using isothermal titration calorimetry (ITC), surface tension measurements, and quartz crystal microbalance with dissipation (QCM-D). ITC data measured in the absence of Ca2+ ions showed the coexistence of exothermic and endothermic processes. The exotherm can be interpreted as the electrostatic binding of the cationic surfactant to the negatively charged LPS membrane surface, whereas the endotherm indicates the hydrophobic interaction between the hydrocarbon chains of the surfactants and LPSs. In the presence of Ca2+ ions, only an exothermic reaction was observed by ITC, and no entropically driven endotherm could be detected. Surface tension experiments further revealed that the co-adsorption of surfactants and LPS was synergistic, while that of surfactants and alcohol was negatively synergistic. Moreover, the QCM-D data indicated that the LPS membrane remained intact when the alcohol alone was added to the system. Intriguingly, the LPS membrane became highly susceptible to the combination of cationic surfactants and aromatic alcohols in the absence of Ca2+ ions. The obtained data provide thermodynamic and mechanical insights into the synergistic function of surfactants and alcohols in sanitation, which will enable the identification of the optimal combination of small molecules for a high hygiene level for the post-pandemic society.

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.

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.

Interfacial properties of cationic and anionic Gemini surfactant mixtures

AbstractThe possibility and the prospect of cationic/anionic (“catanionic”) surfactant mixtures based on sulfonate Gemini surfactant (SGS) and bisquaternary ammonium salt (BQAS) in the field of enhanced oil recovery was investigated. The critical micelle concentration (CMC) of SGS/BQAS surfactant mixtures was 5.0 × 10−6 mol/L, 1–2 orders of magnitude lower than neat BQAS or SGS. A solution of either neat SGS or BQAS, could not reach an ultra‐low interfacial tension (IFT); but 1:1 mol/mol mixtures of SGS/BQAS reduced the IFT to 1.0 × 10−3 mN/m at 100 mg/L. For the studied surfactant concentrations, all mixtures exhibited the lowest IFT when the molar fraction of SGS among the surfactant equaled 0.5, indicating optimal conditions for interfacial activity. The IFT between the 1:1 mol/mol SGS/BQAS mixtures and crude oil decreased and then increased with the NaCl and CaCl2 concentrations. When the total surfactant concentration was above 50 mg/L, the IFT of SGS/BQAS mixtures was below 0.01 mN/m at the studied NaCl concentrations. Adding inorganic salt reduced the charges of hydrophilic head groups, thereby making the interfacial arrangement more compact. At the NaCl concentration was above 40,000 mg/L, surfactant molecules moved from the liquid–liquid interface to the oil phase, thus resulting in low interfacial activity. In addition, inorganic salts decreased the attractive interactions of the SGS/BQAS micelles that form in water, decreasing the apparent hydrodynamic radius (DH, app) of surfactant aggregates. When the total concentration of surfactants was above 50 mg/L, the IFT between the SGS/BQAS mixtures and crude oil decreased first and then increased with time. At different surfactant concentrations, the IFT of the SGS/BQAS mixtures attained the lowest values at different times. A high surfactant concentration helped surfactant molecules diffuse from the water phase to the interfacial layer, rapidly reducing the IFT. In conclusion, the cationic‐anionic Gemini surfactant mixtures exhibit superior interfacial activity, which may promote the application of Gemini surfactant.

Phase Diagram Study of Catanionic Surfactants Using Dissipative Particle Dynamics.

Dissipative particle dynamics (DPD) simulations has been performed to study the phase transition of a mixture of cationic and anionic surfactants in an aqueous solution as a function of the total concentration in water and the relative ratio of surfactants. The impact of the relative difference between the tail lengths of the cationic and anionic surfactants on the phase diagram has been simulated by tuning the number of DPD beads in the simulation model. This research also discusses the impact of the frequently used values of the parameters associated with the harmonic bonds among the bonded DPD beads on the obtained self-assemblies. We find remarkable differences in the resultant self-assemblies based on different choices of harmonic bond parameters. The performed simulations show an enhanced spectrum of self-assemblies with augmented tail lengths and disparate harmonic bond parameters. The obtained self-assemblies are quite unique and can potentially be used in the future for various applications. We also compare the simulation results of the vesicle structures obtained by modeling the electrostatic interaction in the simulation among the charged beads by explicitly introducing charges with a long-range interaction with those obtained by tuning the implicit electrostatic interaction without the long-range interaction. The effects of the chain length of the model and the harmonic bond parameters on the internal density of DPD beads and stress profiles within the vesicles are examined closely. These results are a significant contribution to understanding the stability of the phases and tailoring of the desired vesicles.

Role of mixed surfactants system in preparation of silver nanoparticles

Abstract Different morphologies of silver nanoparticles (AgNPs) are prepared by reducing silver nitrate with hydrazine hydrate in an aqueous solution in the presence of the anionic surfactant sodium 6,6′-((oxybis(ethane-2,1-diyl))bis(oxy))bis(3-dodecanoylbenzenesulfonate) (SOBS), the cationic surfactant cetyltrimethylammonium bromide (CTAB) and mixtures of these two surfactants as template. By mixing these cationic and anionic surfactants, different aggregates (template) were formed. The properties of the nanoproducts are studied by X-ray diffraction, transmission electron microscopy, energy dispersive X-ray analysis and Fourier transform infrared spectroscopy. The results show that the morphology of the nanosilver can be controlled by changing the ratio of cationic to anionic surfactant in the mixture, resulting in silver nanoparticles with high crystallinity and low aggregation.