Ionic Head Groups Research Articles

Synthesis of Asymmetric Ionic Hybrid Detergents enables Micelles with Scalable Properties including Cell Compatibility.

Ionic detergents enable applications and cause harm in biospheres due to cell toxicity. The utility of covalent combinations between ionic and non-ionic detergent headgroups in modulating cell toxicity remains speculative due to the yet rarely explored synthesis. We close this gap and establish the modular synthesis of ionic/non-ionic hybrid detergents. We restructure a combinatorial methallyl dichloride one-pot coupling into a two-step coupling, which reduces by-products, improves product yields, and enables the gram-scale preparation of asymmetric, cationic/non-ionic and anionic/non-ionic hybrid detergents. Our modular synthesis delivers new modalities for the design of ionic detergents, including an unprecedented scaling of properties that determine applications, such as charge, critical micelle concentration, solubilizing properties, hard water tolerance, and cell compatibility. We uncover that shielding the charge in ionic headgroups can switch the detergent species that is toxic to cells from monomers to mixtures of monomers and micellar assemblies. Establishing the chemistry of ionic/non-ionic hybrid detergents provides a missing evolutionary link in the structural comparison of ionic and non-ionic detergents, enables an easy synthesis access to yet unexplored chemical spaces of asymmetric hybrid materials, and delivers new modalities for designing the toxicity of supramolecular nanomaterials.

Probing the heterogeneity of molecular level organization of ionic liquids: a comparative study using neutral Nile red and cationic Nile blue sulfate as fluorescent probes for butyrolactam-based protic ionic liquids.

Ionic liquids (ILs) are liquid salts composed of cations and anions, known for their significant local heterogeneity at the molecular level. To understand the microheterogeneity with regard to their local polarity and local viscosity, we have used two structurally similar but chemically distinguishable fluorescent probes: Nile red (NR), a neutral molecule, and Nile blue sulfate (NBS), a charged molecule. A comparative study of the response of the two probes to the molecular level heterogeneity of ILs is expected to provide a better clarity of understanding regarding the charged polar domain and the uncharged hydrophobic domain of ILs. Towards this, we synthesized two butyrolactam-based protic ionic liquids (PILs), i.e., BTF and BTD, with the same ionic headgroup ([BT]+) and different alkyl tails ([RCOO]-), where {R = H, C11H23}. BTF has no significant hydrophobic domain, whereas BTD has a larger hydrophobic domain. Temperature-dependent fluorescence parameters such as fluorescence intensity, lifetime, and anisotropy were measured for both NR and NBS molecules. The use of a pair of structurally similar but ionically different probes enables differential estimation of parameters like the microviscosity of a domain using the fluorescence anisotropy parameter (r). The absorption and emission spectra of both probe molecules are observed to be blue shifted upon going from BTF to BTD. NR showed a significant blue shift in absorption and emission band maxima. Conversely, NBS exhibited a small wavelength shift, possibly influenced by the preferred location of their charged head group domain. Temperature-dependent rotational relaxation time (θ) of NR in BTD is smaller than that of NBS by 60-70%, indicating that stronger charge-charge interactions exist between the polar domain of BTD and NBS. Moreover, it is observed that the local viscosity of the BTF IL around both probes is similar, whereas there is a considerable difference for the BTD IL. These results are an indication that NBS being charged prefers to locate itself in the charged head group region of the IL, whereas NR being neutral tends to reside both in the hydrophobic domain and in the head group but is predominantly located in the hydrophobic domain.

Characterisation of the apparent aqueous solubility enhancement of testosterone analogues in micelles of dodecyl-chained surfactants with different headgroups

The solubilisation capacities of the micelles formed by a range of surfactants possessing a dodecyl (C12) hydrocarbon ‘tail’ and a variety of hydrophilic ‘headgroups’ have been studied for a range of hydrophobic steroids (testosterone (T) and its propionate (TP) and enanthate (TE) esters). The solubilisation studies were performed at ambient temperature, with drug concentration monitored (over 48–72 h) by UV absorbance. The various surfactant systems were characterised in terms of their physicochemical properties, including their surface tension, critical micelle concentration, viscosity, and density. Results show that while the apparent aqueous solubility of the poorly water-soluble steroids increases upon solubilisation within the surfactant micelles, the extent of this increase varies with the nature of the hydrophilic headgroup and the hydrophobicity of the drug. Specifically, changing the surfactant headgroup from non-ionic to zwitterionic, then to ionic, results in a marked increase in solubility of the two least hydrophobic steroids, testosterone and testosterone propionate, suggesting rather counter-intuitively that these steroidal drugs tend to associate to a greater extent with micelles formed by surfactants with more hydrophilic/charged head groups. The more hydrophobic steroid, TE, was solubilised to the greatest extent, being predominantly solubilised within the micelle core. In this case, the influence of surfactant head group on TE solubilisation was less obvious, with surfactants containing ionic and zwitterionic head groups exhibiting high levels of solubilisation. The physicochemical properties that had most influence on solubilisation of the testosterone analogues, as evaluated using multiple linear regression, were micelle shape for T and TP, and critical micelle concentration for TE. Through the findings of this comparative study, the essential molecular descriptors of optimal solubilisation for improved drug delivery and the loci of solubilisation of the testosterone analogues have been identified.

Facilitating flip-flop: Structural tuning of molecule-membrane interactions in living bacteria

The first barrier that a small molecule must overcome before trespassing into a living cell is the lipid bilayer surrounding the intracellular content. It is imperative, therefore, to understand how the structure of a small molecule influences its fate in this region. Through the use of second harmonic generation, we show how the differing degrees of ionic headgroups, conjugated system, and branched hydrocarbon tail disparities of a series of four styryl dye molecules influence the propensity to “flip-flop” or to be further organized in the outer leaflet by the membrane. We show here that initial adsorption experiments match previous studies on model systems; however, more complex dynamics are observed over time. Aside from probe molecule structure, these dynamics also vary between cell species and can deviate from trends reported based on model membranes. Specifically, we show here that the membrane composition is an important factor to consider for headgroup-mediated small-molecule dynamics. Overall, the findings presented here on how structural variability of small molecules impacts their initial adsorption and eventual destinations within membranes in the context of living cells could have practical applications in antibiotic and drug adjuvant design.

Modification of liposomes composed of a cationic lipid TMAG and an anionic lipid DSPG with a PEGylated lipid based on the investigation of lipid structures

Charged lipids are widely utilized in functional liposomes for controlled release and targeting of drugs. In this study, we prepared the liposomes composed of a cationic lipid N-(α-trimethylammonioacetyl)-distearoyl-D-glutamate chloride (TMAG) and an anionic lipid 1,2-dioctadecanoyl-sn-glycero-3-phospho-1′-rac-glycerol (DSPG) with the molar ratio of TMAG/DSPG = 0:10–10:0 by hydration and extrusion methods. SAXS study for the lipid thin films revealed the formation of lamellar structures of TMAG and DSPG. The lipid thin film, except for the composition of 5:5 and 6:4, formed a liposome with a size of ∼100 nm that could encapsulate riboflavin in the inner aqueous phase. The zeta potentials of liposomes with the composition of 0:10–4:6 showed negative charges, while those of 7:3–10:0 showed positive charges. As the composition approached from 0:10 or 10:0 to 5:5, the phase transition temperature of the lipid bilayer from liquid crystalline phase to gel phase became higher, and the extent of fluorescence anisotropy increased. Thus, the lipid bilayer around the equimolar mixture could form a rigid structure with low fluidity of lipid alkyl chains. The surface charge cancellation by the opposite ionic head groups and the less curvature of the rigid lipid bilayer should prevent the liposomal formation at the composition of 5:5 and 6:4. However, the equimolar composition of 5:5 could form a liposome by the modification of distearoylphosphatidylethanolamine-polyethyleneglycol 2000 (DSPE-PEG2000) into the lipid bilayer at the molar ratio of 4% because it can reduce the rigidity of the lipid bilayer, provide positive curvature to the lipid bilayer, and stabilize the liposome dispersion in water through steric hindrance.

Role of ionic surfactants on the activation of K2S2O8 for the advanced oxidation processes

Effects of cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate were studied to elucidate the persulfate based in-situ chemical oxidation of subsurface contamination. Advanced oxidation processes (AOP) utilizing Fenton’s like reagent was investigated for the degradation of acid orange 7 (AO7) with and without ionic surfactants. The new findings are that the CTAB and SDS retarding the S2O82− activation to some extent. The kinetics of S2O82− assisted decomposition of AO7 were performed under different reaction parameters such as [S2O82−], [Fe2+], [AO7], pH, and temperature. The rate constants (kψ) were decreased markedly in presence of both surfactants. CTAB showed the most potential deactivation than that of SDS. The stability of both surfactants were determined in presence of S2O82−, and no drastic changes was observed in the critical micellar concentration (CMC). The columbic attraction and repulsion between the reactants (S2O82−, and AO7) with ionic head groups of CTAB and SDS are responsible to deactivating the S2O82− decomposition. AO7 and S2O82−, respectively, solubilized and transferred from bulk phase to micellar surface through electrostatic interactions, which may contribute to the inhibitory role of CTAB micelles in the AOP of AO7. Finally the role of surfactants in the Fenton’s like oxidation of AO7 based on the micellar-pseudo phase model was proposed and discussed.

The mechanism for lowering interfacial tension by extended surfactant containing ethylene oxide and propylene oxide groups

In this work, the interfacial tensions (IFTs) of a series of alkyl ether carboxylates containing different ethylene oxide (EO) and propylene oxide (PO) groups (C12PO15EO5C, C12PO15EO10C and C12PO15EO15C) against n-alkanes were investigated. Based on the experimental and theoretic results, we find that for adsorbed extended surfactant molecules with both PO and EO groups, the PO group stretches towards the oil phase in a helical winding manner, which improves the size of hydrophobic part and decreases IFT. On the other hand, the whole EO group arranges in an “L” pattern with 4 EO flat at the interface and the others stretching into the water. The “dumbbell” type with the large size of the ionic head and PO group at both ends and the linear EO chain in the middle results in the high IFT values. Therefore, a sufficient PO number and few EO number are prerequisites for obtaining ultralow IFT. The addition of NaCl can decrease the size of anionic head and C12PO15EO5C solution can produce ultralow IFT against hydrocarbons at optimized salinity. However, electrolyte shows little effect on the IFTs of extended surfactants with “dumbbell” conformation at the interface because the size of linear EO group plays the crucial role. Our research has important implications for the in-depth understanding of extended surfactants and their application in high-salt reservoirs.

A systematic research on spontaneous imbibition of surfactant solutions for low permeability sandstone reservoirs

Surfactants, which possess ability to alter rock surface wettability and reduce interfacial tension (IFT), are effective additives for imbibition enhanced oil recovery (IEOR) in low sandstone permeability reservoirs. However, the imbibition efficiencies vary from different surfactants, and some surfactants even have a negative effect on IEOR. Thus, it is necessary to research optimum surfactants suitable for IEOR. Considering that the surfactant properties are closely related to its molecular structure, this study systematically investigated the static imbibition efficiencies of different surfactants based on molecular structures, which contain different surfactant types, ionic head groups, hydrophilicity, and carbon chain lengths. In addition, the imbibition performance of surfactant solutions with different IFTs were also researched. The imbibition tests were conducted with Amott cells at 80 °C, using Changqing low permeability outcrop sandstones. Subsequently, IFT tests, viscosity measurements, contact angle (CA) measurements, and zeta potential tests were conducted to explore the IEOR mechanisms of different surfactant solutions. The experimental results showed that the IEOR potential of different types of surfactants was: anionic > nonionic > brine > amphoteric > cationic. Sulfate anionic surfactants showed better ability of wettability alteration than sulfonate surfactants, and achieved the most imbibition efficiency. Increasing the hydrophilicity of surfactants by introducing the ethylene oxide (EO) groups to the surfactant structures was effective in enhancing wettability alteration ability of surfactants and improving imbibition recovery. Surfactants with longer carbon chain (C16 surfactants) enhanced more imbibition recovery than short carbon chain surfactants (C12 surfactants), which was mainly depending on better IFT reduction ability of C16 surfactants than C12 surfactants. Appropriate IFT reduction, such as 10−1 mN/m levels, which reduced the adhesion work, enhanced the gravity dominated imbibition and avoided too much capillary pressure reduction, was the most desirable for IEOR. Too low IFTs, such as less than 10−2 mN/m, were not suitable for IEOR, because the capillary pressure reduced greatly, resulting in the imbibition process mainly dominated by gravity. This study provides fundamental information about the selection and design of surfactants for IEOR in low sandstone permeability reservoirs.

Design Principles of Lipid-like Ionic Liquids for Gene Delivery

We developed lipid-like ionic liquids, containing 2-mercaptoimidazolium and 2-mercaptothiazolinium headgroups tethered to two long saturated alkyl chains, as carriers for in vitro delivery of plasmid HEK DNA into 293T cells. We employed a combination of modular design, synthesis, X-ray analysis, and computational modeling to rationalize the self-assembly and desired physicochemical and biological properties. The results suggest that thioamide-derived ionic liquids may serve as a modular platform for lipid-mediated gene delivery. This work represents a step toward understanding the structure-function relationships of these amphiphiles with long-range ordering and offering insight into design principles for synthetic vectors based on self-assembly behavior.

Behavior of CO2 stimulus-responsive amidine naphthenate surfactant: A novel concept for the emulsification

Stimulus-responsive surfactant is becoming a hot research topic with high controllability and excellent emulsifying properties. In this work, an amidine naphthenate surfactant was synthesized for the first time by the reaction between alkyl amidine and naphthenic acid. Surface activity and emulsion performance of this novel surfactant in oil/water emulsion were investigated. Compared with the previously synthesized amidine bicarbonate surfactants, amidine naphthenate surfactants exhibited a superior emulsification performance above 60 °C due to their lower critical micelle concentration (CMC) and interfacial tension (IFT). The presence of two long alkyl groups is recognized as the main reason for its superior properties than amidine bicarbonate having only one long alkyl group. Increased hydrophobic interactions between the long alkyl chains and electrostatic interactions between the ionic head groups lead to the easier formation of micelles. Notably, the amidine naphthenate has a characteristic of CO 2 -responsive property. The amidine naphthenate emulsion can be demulsified by CO 2 bubbling which destroys the chemical structure of amidine naphthenate, accompanied by the formation of amidine cations and naphthenic acids. Then, the emulsion was completely demulsified due to the demulsification effect of naphthenic acid. Therefore, the synthesized amidine naphthenate surfactant possesses not only high interface activity but also CO 2 responsive property, which endows it an extensive application prospect for enhanced oil recovery (EOR) operations in the oil industry. • Amidine naphthenate surfactants with two long alkyl groups and ion groups exhibits superior surface activity. • Amidine naphthenate surfactants has CO 2 -responsive properties. • The oil-water emulsion with amidine naphthenate is stable at 65 °C. • The oil-water emulsion with amidine naphthenate can be broken by bubbling CO 2 .

On the adsorption of n-butane on alkyl imidazolium ionic liquids with different anions using a new molecular beam setup.

The adsorption of reactants is an elementary step in the interaction of molecules with liquid or solid surfaces. We recently reported on the trapping of n-butane on the frozen surfaces of ionic liquids (ILs), namely, 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ILs ([CnC1Im][Tf2N]; n = 1, 2, 3, and 8). To study the influence of the anion, we now present results concerning the trapping of n-butane on 1-alkyl-3-methylimidazolium hexafluorophosphate ILs ([CnC1Im][PF6]; n = 2, 4, and 8), that is, ILs with a smaller anion. The adsorption energies close to zero coverage are determined from the temperature dependence of the initial trapping probability using a novel approach. For both groups of ILs, the binding energy is dominated by the interaction of n-butane with the alkyl chain of the cation, whereas the ionic headgroups contribute only weakly. Comparing ILs with different alkyl chains at the IL cation, we find that the adsorption strength of n-butane increases with increasing length of the alkyl chain. In addition, detailed information on the new setup and the data analysis is provided.

Study on stability of produced water in ASP flooding based on critical micellar theory

The basic properties of produced water and the effect of oil displacement agent for its stability were obtained, through measuring and analyzing water quality characteristics, relationship between critical micelle concentration-oil displacement agent, temperature, pH and content of inorganic salt, particle size distribution and morphology of Nan4-8 and Sanyuan-6 alkali-surfactant-polymer (ASP) produced water of Daqing Oilfield. The critical micelle concentration of ASP flooding was less than its own concentration, and the double bilayer was formed in system. Critical micelle concentration of ASP produced water was less affected by the system temperature and greatly affected by pH. Polymer increases viscosity of produced water and has the properties of surfactant, which partially hydrolyzes under the action of alkali to form polyelectrolyte and promotes the formation of double electric layer. Therefore, the coalescence of oil droplets in ASP produced water is difficult, and the stability is greatly enhanced. ASP produced water contains a large amount of inorganic salts, which can shield the electrostatic repulsion between the surfactant ion head groups, compresses the thickness of the double electric layer, and promotes the formation of surfactant micelles. When it settles after a certain period of time, part of ASP produced water has a particle size distribution less than 100 nm, the micelles are generated in the system, which enhances the stability of ASP produced water.

Anomalously Slow Conformational Change Dynamics of Polar Groups Anchored to Hydrophobic Surfaces in Aqueous Media.

Water molecules within a thin hydration layer, spontaneously generated on hydrophobic protein surfaces, are reported to form a poorly dynamic network structure. However, how such a water network affects the conformational change dynamics of polar groups has never been explored, although such polar groups play a critical role in protein-protein and protein-ligand interactions. In the present work, we utilized as model protein surfaces a series of self-assembled monolayers (SAMs) appended with polar (Fmoc) or ionic (FITC) fluorescent head groups that were tethered via a 1.5-nm-long flexible oligoether chain to a hydrophobic silicon wafer surface, which was densely covered with paraffinic chains. We found that, not only in deionized water but also in aqueous buffer, these oligoether-appended head groups at ambient temperatures both displayed an anomalously slow conformational change, which required ∼10 h to reach a thermodynamically equilibrated state. We suppose that these behaviors reflect the poorly dynamic and low-permittivity natures of the thin hydration layer.

Role of cationic head-group in cytotoxicity of ionic liquids: Probing changes in bilayer architecture using solid-state NMR spectroscopy

The effect of cationic head-group of ionic liquid on the structure and dynamics of phospholipid bilayer was studied to provide insights into the mechanism of ionic liquid-membrane interaction. The effect was observed using six ionic liquids containing benzimidazolium, imidazolium, pyrrolidinium, piperidinium, ammonium, and morpholinium based amphiphilic cations carrying a dodecyl alkyl chain. Unilamellar and multilamellar vesicles composed of zwitterionic 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) were used. Permeability of POPC bilayer was found to have a strong dependence on ionic liquid head-group structure. To probe the structural details of interaction, 31P and 2H based solid-state NMR measurements were performed. The cations differed in terms of their effect on the orientation and disorder in the phosphocholine moiety in lipid head-group as revealed by chemical shift anisotropy of 31P. Cations carrying an unshielded charge like benzimidazolium, imidazolium, and ammonium result in strong reorientation of phosphocholine moiety in lipid head-group. Large sized cations like benzimidazolium and piperidinium result in enhanced lipid chain dynamics as revealed by order parameter calculations of deuterated lipid chains. Relatively polar head-group of morpholinium cation neither impacts the phospholipid head-group nor chain packing. Our results suggest that there exists a direct correlation between ionic liquid head-group induced structural changes in bilayer and their ability to permeabilize/disrupt the membrane and be cytotoxic.

Foaming Agent Developed for Gas Wells with Liquid Loading Problem Using New Surfactant and Nanotechnology

Summary Liquid buildup in the wellbore is one of the major causes of production decline in gas wells, in which case additional energy is needed to drain off the liquid to solve this problem. Foaming agents offer a method to reduce the liquid density to make it easier to be lifted with the gas flow, unloading the accumulated liquid in gas wells. The main ingredient of foaming agents are surfactants. Foam stability is influenced by several factors, such as salinity, temperature, and pressure, so a foaming stabilizer is usually needed for a foam system. A foaming agent should be developed to form stable foams in the presence of a salt or sweet-water hydrocarbon phase at a given temperature and pressure. Recently, various kinds of foaming agents have been developed and discussed. Previous studies mainly focused on the complex interaction between an anionic surfactant and amphoteric ion surfactant; however, stability of the foam system formed by these foaming agents needs to be further improved (Nikolai et al. 2009). Therefore, development of a novel foaming agent with improved stability is necessary, especially for the application under downhole conditions. The complex interaction between the anionic and cationic surfactants is neglected in previous research. For example, the synergies between the anionic and cationic surfactants with appropriate methods can greatly improve the foam stability compared with the one-component system. A complex phase behavior and microstructure that has a high surface activity and foam stability can be obtained by the strong electrostatic interaction between the opposite charge ionic head groups and the hydrophobic interaction between the hydrocarbon groups. A gemini surfactant with a spacer can make the molecules pack tighter and increase the surfactant cohesion within the monolayer, which can greatly enhance the foam stability. The liquid film of foam formed by the surfactant is dynamically unstable because the liquid film cannot prevent the diffusion of gas, and the foam will burst quickly. However, solid films with particles adsorbed in the gas/water interface can weaken the foam drainage speed, so that the foam stability is greatly enhanced. In summary, a robust foaming agent is developed with the introduction of an anionic-nonionic surfactant complexed with a gemini cationic surfactant; moreover, nanoparticles with a certain hydrophilicity and size are also adopted as stabilizers.

On the Dynamic Interaction of n-Butane with Imidazolium-Based Ionic Liquids.

The impact of a reactant from the gas phase on the surface of a liquid and its transfer through this gas/liquid interface are crucial for various concepts applying ionic liquids (ILs) in catalysis. We investigated the first step of the adsorption dynamics of n‐butane on a series of 1‐alkyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide ILs ([CnC1Im][Tf2N]; n=1, 2, 3, 8). Using a supersonic molecular beam in ultra‐high vacuum, the trapping of n‐butane on the frozen ILs was determined as a function of surface temperature, between 90 and 125 K. On the C8‐ and C3‐ILs, n‐butane adsorbs at 90 K with an initial trapping probability of ≈0.89. The adsorption energy increases with increasing length of the IL alkyl chain, whereas the ionic headgroups seem to interact only weakly with n‐butane. The absence of adsorption on the C1‐ and C2‐ILs is attributed to a too short residence time on the IL surface to form nuclei for condensation even at 90 K.

Synthesis and Evaluation of Zwitterionic Surfactants Bearing Benzene Ring in the Hydrophobic Tail.

Surfactant tolerance in the presence of mono and divalent reservoir ions, as well as the solubility of surfactant in high salinity and low salinity brine, are the two major requirements for any surfactant that is subjected to oilfield application. Herein, six poly(ethylene oxide) zwitterionic surfactants having different ionic headgroups and hydrophobic tail were synthesized for oilfield applications. They were characterized by various instrumental techniques (Fourier-transform infrared spectroscopy (FTIR), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF-MS), Nuclear Magnetic Resonance (NMR)) and the combination of these techniques allowed for us to deduce the structure. All of the surfactants revealed prominent solubility in high salinity and low salinity brine due to the presence of ethoxy units between the aromatic ring and amide group. The surfactant samples were oven aged for 90 days at reservoir temperature and a clear solution implies their excellent aqueous stability. Rendering to thermal gravimetric results, decomposition of surfactants was found to occur around 300 °C, which is higher than the reservoir temperature (≥90 °C). It was observed that the hydrophilic headgroup has no significant impact on the critical micelle concentration and other surface properties. However, the hydrophobic tail bearing benzene ring significantly alters the critical micelle concentration and other surface properties.

Ultra-low interfacial tension biobased and catanionic surfactants for low permeability reservoirs

Abstract 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.

Role of Ionic Headgroups on the Thermal, Rheological, and Foaming Properties of Novel Betaine-Based Polyoxyethylene Zwitterionic Surfactants for Enhanced Oil Recovery

Long-term thermal stability of surfactants under harsh reservoir conditions is one of the main challenges for surfactant injection. Most of the commercially available surfactants thermally degrade or precipitate when exposed to high-temperature and high-salinity conditions. In this work, we designed and synthesized three novel betaine-based polyoxyethylene zwitterionic surfactants containing different head groups (carboxybetaine, sulfobetaine, and hydroxysulfobetaine) and bearing an unsaturated tail. The impact of the surfactant head group on the long-term thermal stability, foam stability, and surfactant–polymer interactions were examined. The thermal stability of the surfactants was assessed by monitoring the structural changes when exposed at high temperature (90 °C) for three months using 1H-NMR, 13C-NMR, and FTIR analysis. All surfactants were found thermally stable regardless of the headgroup and no structural changes were evidenced. The surfactant–polymer interactions were dominant in deionized water. However, in seawater, the surfactant addition had no effect on the rheological properties. Similarly, changing the headgroup of polyoxyethylene zwitterionic surfactants had no major effect on the foamability and foam stability. The findings of the present study reveal that the betaine-based polyoxyethylene zwitterionic surfactant can be a good choice for enhanced oil recovery application and the nature of the headgroup has no major impact on the thermal, rheological, and foaming properties of the surfactant in typical harsh reservoir conditions (high salinity, high temperature).

Thermodynamics of Interactions Between Charged Surfactants and Ionic Poly(amino acids) by Isothermal Titration Calorimetry.

Interactions between charges play a role in protein stability and contribute to the energetics of binding between various charged ligands. Ionic surfactants are charged molecules, whose interactions with proteins are still rather poorly understood despite their wide applications. Here, we show by isothermal titration calorimetry that cationic alkylammonium surfactants bind to negatively charged polyaspartate and polyglutamate homopolymers stoichiometrically, i.e., one surfactant molecule per charged amino acid. Similarly, negatively charged alkyl sulfates (e.g., sodium dodecyl sulfate) and alkane sulfonates bind stoichiometrically to positively charged polylysine, polyornithine, and polyarginine homopolymers. In these reactions, the interacting counterparts form ion pairs and the resulting electrostatically neutral complex coprecipitates from solution. The enthalpies and heat capacities are determined for various pairs of ionic surfactants and charged amino acid homopolymers. These results show the energetic contributions of ionic headgroups and the CH2 group to surfactant interactions with proteins.