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Typically, the formation of vesicles requires the addition of salts or other additives to surfactant micelles. However, in the case of catanionic surfactants, unilamellar vesicles can spontaneously form upon dilution of the micellar solutions. Our study explores the intriguing spontaneous vesicle-to-micelle transition in catanionic surfactant systems, specifically cetyltrimethyl ammonium bromide (CTAB) and sodium octylsulfonate (SOS). To gain insights into the changes occurring at the interface, we employ a chemical trapping method to characterize variations in the molarities of sulfonate headgroups, water, and bromide ions during the transition. Our findings reveal the formation of ion pairs between the cationic component of CTAB and the anionic component of SOS, leading to tight interfacial packing in CTAB/SOS solutions. This interfacial packing promotes vesicle formation at low surfactant concentrations. Due to the significant difference in critical micelle concentration (cmc) between CTAB and SOS, an increase in the stoichiometric surfactant concentration results in a substantial rise in the SOS-to-CTAB ratio within the interfacial region. This enrichment of SOS in the aggregates triggers the transition from vesicles to micelles. Overall, our study may shed new light on the design of morphologies in catanionic and other surfactant systems. [ABSTRACT FROM AUTHOR]

Typically, the formation of vesicles requires the addition of salts or other additives to surfactant micelles. However, in the case of catanionic surfactants, unilamellar vesicles can spontaneously form upon dilution of the micellar solutions. Our study explores the intriguing spontaneous vesicle-to-micelle transition in catanionic surfactant systems, specifically cetyltrimethyl ammonium bromide (CTAB) and sodium octylsulfonate (SOS). To gain insights into the changes occurring at the interface, we employ a chemical trapping method to characterize variations in the molarities of sulfonate headgroups, water, and bromide ions during the transition. Our findings reveal the formation of ion pairs between the cationic component of CTAB and the anionic component of SOS, leading to tight interfacial packing in CTAB/SOS solutions. This interfacial packing promotes vesicle formation at low surfactant concentrations. Due to the significant difference in critical micelle concentration (cmc) between CTAB and SOS, an increase in the stoichiometric surfactant concentration results in a substantial rise in the SOS-to-CTAB ratio within the interfacial region. This enrichment of SOS in the aggregates triggers the transition from vesicles to micelles. Overall, our study may shed new light on the design of morphologies in catanionic and other surfactant systems.

A new type of catanionic surfactant phosphonium benzene sulfonate was synthesized by quaternization of triphenyl phosphine with dimethyl carbonate and followed by anion exchange with alkyl benzene sulfonic acid. The molecular structure was characterized by FT-IR, ¹H-NMR, and 31P-NMR. The thermal stability of phosphonium benzene sulfonate was evaluated by thermogravimetric analysis (TGA). Its surface properties were studied systematically through equilibrium surface tension, electrical conductivity, and dynamic surface tension measurements. The wettability, foam properties, and emulsification of phosphonium benzene sulfonate were estimated in this paper. TGA results revealed that it has an excellent thermostability and could be used below 350°C. Equilibrium surface tension results indicated that it has a low critical micelle concentration (CMC, about 0.10mmol/L), lower than that of ammonium benzene sulfonate and sodium dodecyl benzene sulfonate. Furthermore, the micellization of phosphonium benzene sulfonate in aqueous solution is an entropy-driven spontaneous process. The adsorption process of phosphonium benzenesulfonate at the air-liquid interface is controlled by hybrid kinetic adsorption. Moreover, it has excellent wetting and emulsifying properties and low foam properties. [ABSTRACT FROM AUTHOR]

Abstract Foam has been applied in enhanced oil recovery (EOR) for more than sixty years. The surfactant-stabilized N 2 /CO 2 foams are two of the most widely used foams in foam EOR processes, and numerous oil reservoirs could potentially benefit from them. This paper comprehensively reviews the development of these foams over the past decade. We focused on the promising surfactant formulas and their corresponding mechanisms under different reservoir conditions, especially harsh conditions. The most recent studies have shown that low interfacial tension foaming surfactants are efficient in fractured/tight reservoirs, while CO 2 -switchable surfactants are well suited to CO 2 foam in carbonate reservoirs with high temperatures. Pure surfactants and mixed surfactants that combine anions and cations contain superior foam properties. The surfactant aggregates, such as vesicles and wormlike micelles, could distinctly enhance the foam stability. However, the adsorption of the mixed surfactants on reservoir rocks and the temperature sensitivity of the complex structures should be given particular consideration. The phase behaviors involved in foam EOR processes are vital and much more complicated than those in other EOR processes. Thus, a better knowledge of the phase behaviors could further improve foam EOR performance. The results of this paper provide clues to N 2 /CO 2 foam EOR design and also promote the development of harsh reservoirs. [ABSTRACT FROM AUTHOR]

A strategy for aqueous film-forming foam (AFFF) using cationic-anionic surfactant mixtures with short fluorocarbon chains (≤C4) in both cationic and anionic surfactants was proposed. The minimum surface tension (γmin) of mixtures of C4F9SO2NH(CH2)3N(CH3)3I (C4FI) and CnF2n+1COONa (n = 1, 2, 3, 4) with different molar ratios (5:1, 2:1, 1:1, 1:2, 1:5) was measured at 25 °C. The γmin for all mixtures of C4FI-CnF2n+1COONa were remarkably lower than that of pure C4FI. Among these mixtures, the equimolar mixture of C4FI-C3F7COONa was chosen because of the low γmin, qualified solubility and relatively high fluorine efficiency. The spreading coefficients of its aqueous solution on n-heptane, toluene, benzene, cyclohexane and gasoline were all positive, indicative of its potential in AFFF. The film spreading, sealability and foaming were also tested. The influences of 'green' additives (alkyl glucose amide, xanthan gum and sodium carboxymethylcellulose) on foaming performance were studied, in which small dosage of xanthan gum could greatly retard the drainage of foam. It was confirmed that the mixing of oppositely charged surfactants both possessing short fluorocarbon chains was a valuable thought to design AFFF. In application, the quaternary ammonium surfactant likewise can be bromide or chloride rather than iodide for reasons of cost-reduction and stability. [ABSTRACT FROM AUTHOR]

In mixed solutions of anionic and cationic surfactants, called catanionics, ion pairs are formed which behave like non-ionic surfactants with a much higher surface activity than the single components. In equimolar mixtures of NaCnSO4 and CmTAB, all surface-active ions are paired. For mixtures with n + m = const, the interfacial properties are rather similar. Catanionics containing one long-chain surfactant and one surfactant with medium chain length exhibit a strong increase in surface activity as compared with the single compounds. In contrast, catanionics of one medium- and one short chain surfactant have a surface activity similar to that of the medium-chain surfactant alone. Both the Frumkin model and the reorientation model describe the experimental equilibrium data equally well, while the adsorption kinetics of the mixed medium- and short-chain surfactants can be well described only with the reorientation model.

Phase behavior of systems containing sodium dodecyl sulfate (SDS) as anionic surfactant and each of tetraethyl ammonium chloride (TEACl) and tetrabutyl ammonium bromide (TBAB) as cationic hydrotropes in the presence of water and heptane oil was studied. This combination was also used to formulate alcohol-free middle phase microemulsion at different salt concentrations. Anisotropy was detected by cross polarizer and polarized microscopy. Ultralow interfacial tension for microemulsion was calculated theoretically using Chun Huh equation. Micelles and inverse micelles were characterized by conductivity measurements. Liquid crystals did not appear in these short-chain hydrotropic systems. Microemulsion salinity scans for 1% SDS/TBAB (2:1 M ratio) at 25 °C, exhibited Winsor III type at an optimal salinity of 8.5% NaCl, whereas the optimal salinity was found to be 4% NaCl for 8% SDS/TBAB (1:1 M ratio).

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. [ABSTRACT FROM AUTHOR]

Highlights: [•] A rapid synthetic procedure leads to original catanionic perfluoroalkyl hybrid surfactants. [•] These catanionic surfactants exhibited very low surface tension and CMC. [•] TEM images confirmed their tendency to create big spherical aggregates. [Copyright &y& Elsevier]

Highlights: [•] Chain length mismatch in catanionic surfactants induces rich mesomorphism. [•] Unexpected trends in phase transition temperatures and enthalpies are observed. [•] Higher chain asymmetry promotes solid phase stability. [•] Lower asymmetry favors the stability of smectic liquid crystals. [•] Chain interdigitation plays a subtle role in phase organization. [ABSTRACT FROM AUTHOR]

Abstract: A systematic study of the physico-chemical properties of a series of new catanionic surfactants with ionic liquid properties is reported. Importantly, by avoiding environmentally unfriendly halide and imidazolium based moieties highly tunable surfactant ionic liquids have been prepared. [Copyright &y& Elsevier]

Abstract: We report the synthesis of novel chiral catanionic liquid crystals bearing camphorsulfonamide substructures. The phase behaviour of these long-chain substituted imidazolium sulphates and sulfonates was investigated using X-ray diffraction (XRD), polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). We observed that the phase behaviour clearly depends on the substitution of both cation and anion. The chiral camphorsulfonamide substructures have an unfavourable influence on the formation of liquid crystalline (LC-) phases. Contrary to N,N′-di-alkyl-imidazolium salts, the formation of LC phases was only observed when both cation and anion are substituted with long alkyl chains (C12 or C16). Furthermore, the phase transition temperatures depend on the chain length of the alkyl groups, as higher phase transition temperatures were observed for compounds bearing longer alkyl chains. However, no macroscopic evidence for the formation of chiral mesophases was obtained. [Copyright &y& Elsevier]

Abstract: A model of helical spring is described whose effective pitch and length are decided by the balance of the attractive van der Waals and repulsive hydration and electrical double layer forces. Also the electric contribution to the curvature free energy is taken into account. The stability of the nanospring is investigated and it is shown that the spring becomes unstable and jumps to its extended state on increase of electrostatic repulsion beyond a limit implying a jump in viscosity of suspension of springs in the solution. The magnitude of the jump and threshold potential are investigated. [ABSTRACT FROM AUTHOR]

Like other amphiphilic compounds, bolaforms do not always possess surfactant properties; it depends on the spacer chain length and the nature of the polar head group (both sufficiently hydrophobic or hydrophilic, respectively, to intensify the amphiphilic properties). In this regard, unsymmetrical bolaamphiphiles bearing a sugar polar head group and a carboxylic acid function at the opposite ends of a hydrophobic binding spacer were synthesized. These biocompatible sugar-derived bolaforms were associated with basic fatty amines, by an acid-base reaction, to obtain catanionic mixtures. Associations with 1,7-lactobionamidoheptanoic acid and decylamine or octylamine spontaneously form stable 200-600 nm vesicles. This new type of association may find an application in drug delivery since catanionic vesicles can transport active substances inside the hydrophilic core, as well as hydrophobic drugs within the bilayer. [ABSTRACT FROM AUTHOR]

Abstract: We report in this work on the scaling behavior of wormlike micelles formed in a series of mixed systems of oppositely charged surfactants, including sodium decanote (SD)/hexadecyltrimethylammonium bromide (CTAB), sodium laurate (SL)/hexadecyltrimethylammonium bromide, sodium didecaminocystine (SDDC)/hexadecyltrimethylammonium bromide, and sodium dilauraminocystine (SDLC)/hexadecyltrimethylammonium bromide. Steady and dynamic rheological measurements were performed to characterize these wormlike micelles. The scaling behavior for these systems at various mixing ratios was systematically investigated and was compared with that given by the Cates model. It was found that the Cates law can be applied in these systems simply by manipulating the mixing ratio or the surfactant structure. Energetic analysis demonstrates that the scaling behavior of wormlike micelles in nonequimolar mixed cationic and anionic surfactant systems can be close to that predicted by the Cates model, if the electrostatic contribution is below a threshold value. [Copyright &y& Elsevier]

Abstract: The phase behavior of oil–water–surfactant systems was determined for alcohol-free mixtures of anionic and cationic surfactants in which the principal anionic surfactants were propoxylated sulfates whose hydrophobe consisted of a long, straight chain with randomly located methyl groups. The cationic surfactants, used mainly in smaller amounts than the anionics, had hydrophobes which were short and/or branched hydrocarbon chains or, in one case, a propylene oxide chain. When the oil was a West Texas crude oil and the formulation included sodium carbonate to convert naphthenic acids in the crude oil to soaps, salinity scans revealed that small amounts of some cationic surfactants increased solubilization of oil and brine in the microemulsion phase near “optimal” salinity, where equal volumes of oil and brine are solubilized and interfacial tensions (IFT''s) are low. Measurements of IFT between microemulsion and brine at optimal conditions in one of these systems showed that IFT decreased from approximately 0.007 to 0.001mN/m when a small amount of cationic surfactant was added, as would be expected with the higher solubilization. [Copyright &y& Elsevier]

Abstract: Cryogenic transmission electron microscopy (cryoTEM) was used to study the structures formed in mixtures of sodium dodecylsulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) in dilute aqueous solutions with 0–300 mM NaBr. The DTAB mole fraction, X, was in the range 0.2–0.4, limited at 25 °C by precipitation of solid DTA–DS at without salt to at 300 mM NaBr. At a total surfactant concentration of 100 mM the samples separated into two liquid phases (the bottom phase birefringent) within a narrow (±0.01 mole fraction units) composition range. At the mid-point X varied from 0.32 without salt to 0.22 at 300 mM NaBr. Elemental analysis of C, S, O, and N in the separated phases of a sample with 100 mM NaBr and showed the top phase to contain almost only SDS at a low concentration, 14 mM, and the bottom phase 175 mM total surfactant, with . Elemental analysis on samples without added salt gave erratic results, indicating problems in the physical separation of the phases. The cryoTEM survey of the separated phases revealed similar problems. Without salt both phases showed similar structures, whereas the top phase in the sample with added salt was void of structures larger than small micelles. The cryoTEM survey revealed a variety of structures being simultaneously present in most samples. A general trend with increasing X was an evolution from globular micelles, over disks, bands, branched bands transforming into sparse webs, perforated bilayer structures, and finally smooth bilayers. Increasing salt and total surfactant concentrations resulted in the emergence of structures with smaller mean curvature at lower X. Perforated bilayers were found in samples with 100 mM or less of added salt, and usually persisted to DTAB contents where precipitates appeared. The porous bilayers seemed to derive from sparse webs of band-like structures, and the hole size decreased with increasing X and salt concentration. Two types of recurrent structures were noticed: blastula aggregates, seemingly an intermediate structure transforming crumpled bilayers into vesicles of similar size (diameter 400–500 Å), observed over a broad range of conditions, and at 100 mM total surfactant concentration and 50 mM added salt or more a type of regular disks with a diameter of . [Copyright &y& Elsevier]

Abstract: The interaction between sodium perfluorooctanoate (SPFO) and dodecyltrimethylammonium bromide (DTAB) was studied by several methods and it was found strongly synergistic. Above a mole fraction of SPFO in the surfactant mixture , the interaction is repulsive and increases with the content of SPFO in both, the overall mixture and micelles, whereas the interaction is attractive if DTAB is in excess. At the low miscibility between hydrocarbon and fluorocarbon is counterbalanced by the electrostatic attraction between the opposite charged head groups, and the micelle composition is ideal (i.e., the mole fraction of SPFO in micelles ). The solubility of fluorocarbon in hydrocarbon is lower than that of hydrocarbon in fluorocarbon. Micelles of DTAB act as a solvent for SPFO without important structural changes, whilst micelles of SPFO undergo important changes when dissolve DTAB. This asymmetry may be interpreted as caused by the difference in chain length that favors the inclusion of the shorter chain in micelles of the longer surfactant, but disfavors the opposite process. Above there is an excess adsorption of bromide ions on the mixed micelles surface, giving rise to a high ζ potential. Micelles of pure SPFO or pure DTAB show an important energy barrier which prevents micelle flocculation. The inclusion of SPFO in DTAB micelles produces a reduction of the energy barrier, which disappeared when . This produces the flocculation of micelles giving rise to the formation of a non-birefringent coacervate, which is probably formed by unordered isometric clusters of micelles. [Copyright &y& Elsevier]

Abstract: In a first part, the comprehension of the antiviral efficiency of a Gemini catanionic analogue of GalCer Gem16-12-16 is deepened by studying its interactions with phospholipids. Monolayers at the air/water interface are used as 2D models of biological membrane. Adsorption kinetics measurements are performed at Gemini concentrations below the critical aggregation concentration (CAC) and show an incorporation of Gem16-12-16 molecules into the fluid phase as well as into the condensed domains of a DPPC monolayer. Compressing such a mixed monolayer leads first to the squeezing out of Gem16-12-16 molecules from the fluid part of the monolayer and above 30mN/m to the squeezing out from the condensed part. SAXS/WAXS studies are performed using mixtures of Gem16-12-16 catanionic surfactant and DPPC. Bilayers have been observed at high concentrations for Gem16-12-16 in water, in a large temperature range. Mixing with DPPC produces mixed bilayers above the corresponding chain melting temperature. At room temperature, partially lamellar aggregates with local nematic order are observed. In a second part, the ability to encapsulate anti-HIV drugs of another analogue of GalCer Tri16-12-12 is studied. A difference in monolayer stability of pure Tri16-12-12 is observed on water or on buffer subphases, encouraging us to perform the first encapsulation assays in buffer solutions. First results on a fluorescent probe entrapment inside the vesicles are performed in order to validate the use of these vectors in anti-HIV therapy. [Copyright &y& Elsevier]

The interactions of alkylammonium chlorides (the number of carbon atom per chain was either 12, 14, or 16) with sodium cholate have been investigated by a combination of techniques including light and electron microscopy, surface tension, conductivity, light scattering, and microelectrophoretic measurements. The phase behavior has strongly depended on the molar ratio and actual concentration of oppositely charged surfactants. The change in the composition of the aggregates leads to a shape transformation from globular to elongated micelles to open and/or closed bilayers (vesicles) and precipitation. The length of micelles has been found to decrease dramatically with the concentration shift to the micellar regions of either surfactant. Upon a moderate excess of one surfactant, the mean hydrodynamic diameter of aggregates increases and wormlike micelles and/or open and closed bilayers are formed. Microscopic observations of alkylammonium cholates (novel catanionic surfactants precipitated in and/or close to equimolar region) have shown the presence of a variety of morphologies including twisted ribbons, tubules and bundles of tubules. [ABSTRACT FROM AUTHOR]

Abstract: Catanionic surfactants formed by the pairing of two ionic amphiphilic chains of opposite charge are now recognized as an important class of amphiphiles. Many aspects of their phase behavior have yet to be explored. In this work, two homologous series of catanionic surfactants were synthesized, based on the cationic headgroups trimethylammonium and pyridinium. Within each series, the headgroup and chain length of the cationic counterpart remains constant while for the anionic counterpart the headgroup is varied, while its alkyl chain length is also kept constant. Thus, one can directly monitor the influence of headgroup chemistry on the thermal behavior of these compounds. Differential scanning calorimetry (DSC) and polarizing light microscopy show that these compounds bear a rich and often complex thermotropic behavior, with the headgroup chemistry in some instances having a rather dramatic influence on phase behavior. Several liquid crystalline phases appear between the solid crystalline phase and the isotropic liquid phase. A qualitative correlation between the observed thermotropic behavior and the chemical nature of headgroup is presented. [Copyright &y& Elsevier]

Abstract: Interactions between poly(ethylene oxide) (PEO), and equimolar mixed sodium decylsulfonate and decyltriethylammonium bromide were studied using surface tension, fluorescence, dynamic light scattering and freeze-fracture transmission electron microscopy techniques. Below the cmc of the equimolar mixed cationic–anionic surfactants, no obvious interaction was observed under the experimental conditions. However, PEO had dramatic effects on the morphology of the aggregates of the equimolar mixed cationic–anionic surfactants. Spontaneous, stable and narrow distributed vesicles could be prepared by mixing PEO and equimolar mixed cationic–anionic surfactants. Furthermore, the size of the vesicles could be controlled by turning the total surfactant concentration, PEO concentration and PEO molecular weight. We found the effect of PEO on the vesicles could be explained by the Asakura–Oosawa model. [Copyright &y& Elsevier]

The studies of temperature dependent transitions of bilayer structures are mainly focused on phospholipids systems. Since the appearance of catanionic surfactants it is possible to study another type of bilayer structure but as they were prepared until recently in the presence of initial counter-ions, the electrostatic interactions could not be taken in account. Our aim is to present some differential scanning calorimetry results of salt-free catanionic systems prepared with acid surfactant and hydroxide surfactant, and to compare them with literature data. [Copyright &y& Elsevier]

Self-organization in aqueous systems based on ionic surfactants, and their mixtures, can be broadly understood by a balance between the packing properties of the surfactants and double-layer electrostatic interactions. While the equilibrium properties of micellar systems have been extensively studied and are understood, those of bilayer systems are less well characterized. Double-chained and pseudodouble-chained (or catanionic) surfactants are among the amphiphiles which typically form bilayer structures, such as lamellar liquid–crystalline phases and vesicles. In the past 10–15 years, an experimental effort has been made to get deeper insight into their aggregation patterns. With the double-chained amphiphiles, by changing counterion, adding salt or adding anionic surfactant, there are possibilities to depart from the bilayer aggregate in a controlled manner. This is demonstrated by several studies on the didodecyldimethylammonium bromide surfactant. Mixtures of cationic and anionic surfactants yield the catanionics, surfactants of the swelling type, and also show a rich phase behavior per se. A variety of liquid–crystalline phases and, in dilute regimes, equilibrium vesicles and different micellar shapes are often encountered. Phase diagrams and detailed structural studies, based on several techniques (NMR, microscopy and scattering methods), have been reported, as well as theoretical studies. The main features and conclusions emerging from such investigations are presented. [Copyright &y& Elsevier]

The solubilization of styrene in micelles of the catanionic surfactant dodecyltrimethylammonium hydroxide (DTAOH)– n-dodecane-phosphonic acid (DPA) was studied by UV–Vis. spectrometry, as a function of the DTAOH:DPA proportion in the surfactant mixture. The styrene molecules are adsorbed at the surface of the micelles, with the vinyl group closer to the hydrocarbon core than the aromatic ring, which is oriented to the water. In micelles with an excess of DTAOH, the dielectric constant of the water surrounding the micelles was strongly affected by the non-neutralized – N(CH3)+ 3 groups at the Stem layer. In micelles with an excess of DPA, the –PO3H2 groups which are not neutralized by – N(CH3)+ 3, remain almost unionized and hydrogen-bonded. The effect of the micellar surface on the surrounding water dielectric constant dropped sharply. The dielectric constant in the hydrogen-bonded polar layer is ∼65, rising to the value of pure water very close to the micellar surface. [ABSTRACT FROM AUTHOR]

Alkyl polyglucoside, an eco-friendly, stable and low-cost available biobased surfactant, was chemically modified to develop ultra-low interfacial tension (IFT) surfactants for crude oil recovery from low permeability reservoirs. The modified anionic surfactant alkyl polyglucoside sodium hydroxypropyl sulfonate (APGSHS) was structurally characterized by FT-IR, 1H NMR and TGA methods. Following that, the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) was combined with APGSHS to formulate the ultra-low oil/water IFT catanionic surfactants, which exhibits higher water-solubility than DTAB/APGSHS mixtures at various concentrations and combined ratios. Furthermore, the surface properties, thermodynamic parameters of the sole and combined surfactants show that the combined APGSHS/CTAB catanionic surfactants have lower surface tension (22.90 mN/m) at cmc , smaller area occupied per molecule and stronger micellization capacity, which indicates that the surfactant molecules are tightly absorbed onto the two-phase interface for catanionic surfactants. The mechanism underlying the strong electrostatic attraction between the ion head groups in APGSHS and CTAB could be proven by the high absolute value of interaction parameters (12.23) in binary systems. Besides, the salinity resistance effect tests indicate that the ultra-low IFT formula exhibits excellent performance in both monovalent and divalent ions conditions. Notably, the APGSHS/CTAB surfactants with total concentration of 3000 mg/L and molar ratio of 6:4 can effectively enhance oil recovery and decrease the injected pressure for low permeability reservoirs. Hence, the newly formulated green catanionic surfactants exhibit remarkable abilities for maintaining the ultra-low IFTs and can be used for EOR in low permeability and high salinity reservoirs. Unlabelled Image • A biobased surfactant alkyl polyglucoside is chemically modified for crude oil recovery from low permeability reservoirs. • Ultra-low interfacial tension (IFT) catanionic surfactants were formulated. • The ultra-low IFT formula exhibits excellent tolerance capacities against both monovalent and divalent ions. [ABSTRACT FROM AUTHOR]

Phase behavior of systems containing sodium dodecyl sulfate (SDS) as anionic surfactant and each of tetraethyl ammonium chloride (TEACl) and tetrabutyl ammonium bromide (TBAB) as cationic hydrotropes in the presence of water and heptane oil was studied. This combination was also used to formulate alcohol-free middle phase microemulsion at different salt concentrations. Anisotropy was detected by cross polarizer and polarized microscopy. Ultralow interfacial tension for microemulsion was calculated theoretically using Chun Huh equation. Micelles and inverse micelles were characterized by conductivity measurements. Liquid crystals did not appear in these short-chain hydrotropic systems. Microemulsion salinity scans for 1% SDS/TBAB (2:1 M ratio) at 25 °C, exhibited Winsor III type at an optimal salinity of 8.5% NaCl, whereas the optimal salinity was found to be 4% NaCl for 8% SDS/TBAB (1:1 M ratio). [ABSTRACT FROM AUTHOR]

Effective and efficient spreading of drug formulations on the pulmonary mucosal layer is key to successful delivery of therapeutics through the lungs. The pulmonary mucus layer, which covers the airway surface, acts as a barrier against therapeutic agents, especially in the case of chronic lung diseases due to increased thickness and viscosity of the mucus. Therefore, spreading of the drug formulations on the airways gets harder. Although spreading experiments have been conducted with different types of formulations on mucus-mimicking subphases, a highly effective formulation is yet to be discovered. Adding surfactant to such formulations decreases the surface tension and triggers the Marangoni forces to enhance the spreading behavior. In this study, catanionic (cationic + anionic) surfactant mixtures composed of dodecyltrimethylammonium bromide (DTAB) and dioctyl sulfosuccinate sodium salt (AOT) mixed at various mole ratios are prepared and their spreading behavior on both mucin and cystic fibrosis (CF) mucus models is investigated for the first time in the literature. Synergistic interaction is obtained between the components of the DTAB/AOT mixtures, and this interaction has enhanced the spreading of the formulation drop on both the mucin and CF mucus models when compared with the spreading performances of selected conventional surfactants. It is proposed that the catanionic surfactant mixtures, especially when mixed at the molar ratios of 8/2 and 7/3 (DTAB/AOT), improve the spreading even on the cystic fibrosis sputum model. As it is vital to transport a sufficient amount of drug to the targeted region for the treatment of diseases, this study presents an important application of the fundamentals of colloidal science to pharmaceutical nanotechnology.