Surfactant Structure Research Articles

Synthesis and effect of the structure of bithienyl-terminated surfactants for dielectric layer modification in organic transistor

Synthesis and effect of the structure of bithienyl-terminated surfactants for dielectric layer modification in organic transistor

Very low surface tensions with “Hedgehog” surfactants

Previous studies [Langmuir, 2014, 30, 21, 6057–6063, Phys. Chem. Chem. Phys., 2017,19, 23869–23877] have shown that surfactants bearing highly-methylated alkyl tails (so-called “hedgehog” groups) are able to reduce the limiting surface tension at the aqueous critical micelle concentration (CMC) to γCMC ~24 mN m−1, which is considerably lower than for common n-alkyl tail surfactants (30–40 mN m−1). In the quest to develop even more effective and efficient non-fluorinated surfactants, this study introduces new amphiphiles having double and triple hedgehog tails and examines relationships between surfactant structure and aqueous solution properties. Of particular interest are links between γCMC, the effective hydrophobic-tail layer density (ρlayer) and total number of carbon and silicon atoms in the hydrophobic tails (NC+Si). Interestingly, γCMC is seen to depend on ρlayer rather than NC+Si, and ρlayer ~0.63 g cm−3 appears to be an optimal surface layer density for promoting low γCMC. For a surfactant bearing trimethysilyl (TMS) chain tips, exchanging the surfactant counterions from Na+ to Mg2+ reduced γCMC from 23.8 mN m−1 to 21.5 mN m−1, which is very low for a hydrocarbon surfactant, and comparable to typical fluorinated surfactants. A new measure of the ability of different surfactants to lower surface tension is proposed, which is helpful for targeting low surface energy (tension) non-fluorinated surfactants. In terms of both γCMC and CMC TMS-terminal tips are shown to be key groups for promoting hydrophobicity and/or low surface tensions.

Spotlight onto surfactant\u2013steam\u2013bitumen interfacial behavior via molecular dynamics simulation

Heavy oil and bitumen play a vital role in the global energy supply, and to unlock such resources, thermal methods, e.g., steam injection, are applied. To improve the performance of these methods, different additives, such as air, solvents, and chemicals, can be used. As a subset of chemicals, surfactants are one of the potential additives for steam-based bitumen recovery methods. Molecular interactions between surfactant/steam/bitumen have not been addressed in the literature. This paper investigates molecular interactions between anionic surfactants, steam, and bitumen in high-temperature and high-pressure conditions. For this purpose, a real Athabasca oil sand composition is employed to assess the phase behavior of surfactant/steam/bitumen under in-situ steam-based bitumen recovery. Two different asphaltene architectures, archipelago and Island, are used to examine the effect of asphaltene type on bitumen's interfacial behavior. The influence of having sulfur heteroatoms in a resin structure and a benzene ring's effect in an anionic surfactant structure on surfactant–steam–bitumen interactions are investigated systematically. The outputs are supported by different analyses, including radial distribution functions (RDFs), mean squared displacement (MSD), radius of gyration, self-diffusion coefficient, solvent accessible surface area (SASA), interfacial thickness, and interaction energies. According to MD outputs, adding surfactant molecules to the steam phase improved the interaction energy between steam and bitumen. Moreover, surfactants can significantly improve steam emulsification capability by decreasing the interfacial tension (IFT) between bitumen and the steam phase. Asphaltene architecture has a considerable effect on the interfacial behavior in such systems. This study provides a better and more in-depth understanding of surfactant–steam–bitumen systems and spotlights the interactions between bitumen fractions and surfactant molecules under thermal recovery conditions.

Activity of Polyphenoloxidase in red Fuji Apples Promoted with Cationic Surfactant – Role of Surfactant Structure

Abstract In this study, we observed the activity of polyphenoloxidase (PPO) in red Fuji apples in the presence of single-chained surfactants (including cetyl trimethyl ammonium bromide (CTAB), and dodecyl trimethyl ammonium bromide (DTAB)) and gemini surfactants (pentamethylene-α,ω-bis(dodecyl dimethyl ammonium bromide), octamethylene-α,ω-bis(dodecyl dimethyl ammonium bromide, dodecamethylene-α,ω-bis(dodecyl dimethyl ammonium bromide), pentamethylene-α,ω-bis(cetyl dimethyl ammonium bromide), and octamethylene-α,ω-bis(cetyl dimethyl ammonium bromide)). It was found that all these surfactants enhanced the activity of PPO in a wide range of temperature at low content. When PPO was denatured by incubating at high temperature, the surfactants caused reactivation of PPO. Compared to the single-chained surfactants, the gemini surfactants increased PPO activity at a much lower concentration. Moreover, the single-chained surfactant and the gemini surfactant acted together to further increase PPO activity, and the synergistic effect reduced the amount of surfactant used. In addition, the Michaelis-Menten constant for PPO did not change in the presence of the surfactants, suggesting the active site should remain well with the surfactants.

The effect of head group of surfactant on the adsorption of methyl red onto modified coffee residues

The effect of the head group structure of surfactant on the adsorption of methyl red (MR) onto modified coffee residues (MCRs) has been investigated. The coffee residue (CR) was modified by a cationic surfactant, namely Dodecyltrimethyl ammonium bromide (DTAB) and a zwitterionic surfactant, namely N, N-Dimethyldodecylamine N-oxide (DDAO). The CR and MCRs (DTAB–CR and DDAO–CR) were characterized by using SEM, EDX, BET and FTIR analysis. The effect of pH, contact time and initial MR concentration on the adsorption process was studied. Langmuir and Freundlich isotherm models were used to evaluate the experimental data. Adsorption equilibrium data were fitted to Langmuir isotherm, and the maximum adsorption capacities with DTAB–CR and DDAO–CR was 66.66 and 76.72 mg/g, respectively. On the other hand, the results of kinetic studies showed that the data were in maximum agreement with the pseudo-second-order kinetic model. Based on the experimental data and the proposed adsorption mechanism, it was concluded that zwitterionic surfactant is the most efficient for the adsorption of MR.

Adsorption and Aggregation Behavior of Mixtures of Quaternary-Ammonium-Salt-Type Amphiphilic Compounds with Fluorinated Counterions and Surfactants.

The surface adsorption and aggregation behavior of a mixture of quaternary-ammonium-salt-type amphiphilic monomeric compounds (C4 FSA, C8 FSA, and C4 NTf2) or gemini compounds (C10-2-C4 FSA) and various surfactants (nonionic hexaoxyethylene dodecyl ether (C12EO6), anionic sodium dodecyl sulfate (SDS), cationic dodecyltrimethylammonium bromide (C12TAB), and zwitterionic N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (C12Sb)) was investigated. Both types of compounds contained alkyl chains of nonidentical lengths that used bis(fluorosulfonyl)imide (FSA-) or bis(trifluoromethanesulfonyl)imide (NTf2-) as counterions. The mixtures were analyzed for surface tension, viscosity, electrical conductivity, and pyrene fluorescence, in addition to evaluation by cryogenic transmission electron microscopy, small-angle X-ray scattering, and dynamic light scattering. Our results showed that the surface tension depended on the surfactant structure. For the mixture of C8 FSA and SDS, as the SDS concentration increased, the surface tension first decreased and became constant at the critical micelle concentration (CMC). In this concentration range, C8 FSA and SDS were approximately equimolar (2.5 mmol dm-3), the mixture adsorbed efficiently at the air-water interface, and vesicles and linear-type micelles were formed in the solution owing to the decreased electrostatic repulsion between the hydrophilic groups. As the SDS concentration further increased, the surface tension increased and reached another constant value. The C8 FSA at the interface was replaced by SDS and the aggregates transformed into spherical micelles. The surface tension plot of the mixture of the amphiphilic compounds and C12Sb showed a minimum at the CMC. The lowest CMC and surface tension were observed for C10-2-C4 FSA, indicating that the gemini compounds offer excellent adsorption and orientation at the air-water interface. It was revealed that the quaternary-ammonium-salt-type amphiphilic compounds in this study acted as ionic liquids on their own and as surfactants in aqueous solution. Further, they could improve the surface activity of conventional ionic surfactants.

Predicting Critical Micelle Concentrations for Surfactants Using Graph Convolutional Neural Networks.

Surfactants are amphiphilic molecules that are widely used in consumer products, industrial processes, and biological applications. A critical property of a surfactant is the critical micelle concentration (CMC), which is the concentration at which surfactant molecules undergo cooperative self-assembly in solution. Notably, the primary method to obtain CMCs experimentally-tensiometry-is laborious and expensive. In this study, we show that graph convolutional neural networks (GCNs) can predict CMCs directly from the surfactant molecular structure. In particular, we developed a GCN architecture that encodes the surfactant structure in the form of a molecular graph and trained it using experimental CMC data. We found that the GCN can predict CMCs with higher accuracy on a more inclusive data set than previously proposed methods and that it can generalize to anionic, cationic, zwitterionic, and nonionic surfactants using a single model. Molecular saliency maps revealed how atom types and surfactant molecular substructures contribute to CMCs and found this behavior to be in agreement with physical rules that correlate constitutional and topological information to CMCs. Following such rules, we proposed a small set of new surfactants for which experimental CMCs are not available; for these molecules, CMCs predicted with our GCN exhibited similar trends to those obtained from molecular simulations. These results provide evidence that GCNs can enable high-throughput screening of surfactants with desired self-assembly characteristics.

Microscopic mechanisms of inorganic salts affecting the performance of aqueous foams with sodium dodecyl sulfate: View from the gas–liquid interface

Inorganic salts contained in wellbore accumulations have a significant impact on the suitability and effectiveness of foam draining technology in gas wells. Despite many studies on the effects of such salts on the stability of water-based foams generated by surfactant, the findings are not conclusive due to the differences in surfactant structures and research methods used. In order to gain a better understanding of the influence of inorganic salt types and concentrations on foam systems containing sodium dodecyl sulfate (SDS), a combined experimental and molecular simulation-based approach was used. The experimental results showed that MgCl2 significantly improves the stability of the SDS foam system, while NaCl greatly improves its liquid carrying capacity. Distinguishing from the traditional classification including foam generation, gas coarsening and bubble rupture, the process of foam system from generation to rupture was divided into three new stages, as manifest in foam generation, liquid drainage and gas transfer. In conjunction with molecular dynamics simulations, the effect of MgCl2 and NaCl on these three stages was explored. In addition, the microscopic mechanisms by which MgCl2 and NaCl influenced the stability and liquid-carrying properties of the SDS foam system were clarified. It was found that MgCl2 improved the foam stability by reducing the gas–liquid interfacial tension and enhancing the strength of the interface containing SDS, while NaCl improved the liquid-carrying capacity of the SDS foam system through hydration. The understanding of this study is of great importance for the application of aqueous foams with SDS in upstream natural gas industry.

Foaming behavior of sugar-based surfactants: influence of molecular structure and anticipation from surface properties

Sugar-based surfactants are a class of environmentally-friendly surface-active molecules well known for their functional performances, good biodegradability and reduced ecological footprint. Many previous studies have explored the surface properties of these surfactants. However, very little research has investigated their foaming properties. The present study examines the foaming behavior of 17 nonionic sugar-based surfactants with gradual structure variation. Foaming properties such as foamability, foam stability and maximum foam density were measured using the gas-sparging method. The influence of surfactant structure and concentration on foaming properties was evaluated. The data on surface adsorption properties, determined in the previous study, and foaming properties were then analyzed using a Principal Component Analysis. It was shown that the foaming behavior of glycolipids can be correlated to concentration and interfacial properties. Predictive models are proposed to anticipate the foaming behavior and provide a useful guide for screening the foamability of bio-based surfactants in various technological applications.

Polyamide Nanofiltration Membranes from Surfactant‐Assembly Regulated Interfacial Polymerization: The Effect of Alkyl Chain

AbstractRegulating the monomer diffusion during interfacial polymerization (IP) process is the key for tailoring the pore structure and desalination performance of thin‐film composite polyamide nanofiltration (NF) membrane. Recently a surfactant‐assembly strategy to regulate IP process and NF membranes with sub‐Å separation precision is proposed. However, little is known for the role of the molecular structure of surfactant on IP process and membrane performance. In this work, five sulfate surfactants with different length of alkyl chains are used to construct surfactant monolayer assembly at the water/hexane interface to regulate IP process. The results show that for the sulfate surfactants, the longer the alkyl chain, the more uniform the pore size distribution of polyamide active layer is and the higher the ion separation selectivity of NF membrane is. Among them, the NF membrane prepared from sodium n‐hexadecyl sulfate (SHS) exhibits the highest separation performance with the rejection of Na2SO4, MgSO4, MgCl2, and CaCl2 up to 99.39%, 99.12%, 98.09%, and 97.38%, respectively. Overall, this study further confirms the regulatory role of surfactant‐assembled monolayer during IP process and provides important insights into how the polyamide structure and the resulting NF membranes are influenced by the alkyl chain length of the surfactants.

Formation of micro/nanoparticles and microspheres from polyesters by dispersion ring‐opening polymerization

AbstractThe micro/nanoparticles and microspheres of polyesters derived from the heterocyclic monomers of lactide (L,L or D,L), ε‐caprolactone, and glycolide have received significant interest as drug carriers for biomedical applications. This review focuses on the recent advances in the study of polyester‐based micro/nanoparticles and microspheres derived from the dispersion ring‐opening polymerization (ROP) of heterocyclic monomers, and/or self‐assembly of polyester macromolecules, and/or dialysis of polyester solution in water‐miscible organic solvents against water. The dispersion polymerization of heterocyclic monomers in the presence of non‐polar miscible solvents and amphiphilic polymer surfactant leads to the formation of polyester particles with a narrower size distribution. The use of the polymer surfactant is crucial in controlling the diameter, morphology, and stability of the polyester particles formed during the ROP. The polymer surfactant acts as a stabilizer and is bound to the polyester particles strongly and irreversibly to control the size and morphology of polyester microspheres. The properties of polyester particles are varied by controlling the number average diameter and diameter polydispersity index. Hence, in this article, we review different synthetic strategies developed for the formation of polyester based particles with controlled diameter of distribution and the factors influencing its formation such as structure of the polymer surfactant, critical micelle concentration of the surfactant, type of radical initiator/monomer used, reaction parameters, etc. The article also describes methods developed for transforming the polyester microspheres into the water for better biocompatibility and encapsulation of bioactive compounds, drugs, and proteins into the polyester particles and their potential release at the targeted specific site are reviewed.

Human Surfactant Protein SP-A1 and SP-A2 Variants Differentially Affect the Alveolar Microenvironment, Surfactant Structure, Regulation and Function of the Alveolar Macrophage, and Animal and Human Survival Under Various Conditions.

The human innate host defense molecules, SP-A1 and SP-A2 variants, differentially affect survival after infection in mice and in lung transplant patients. SP-A interacts with the sentinel innate immune cell in the alveolus, the alveolar macrophage (AM), and modulates its function and regulation. SP-A also plays a role in pulmonary surfactant-related aspects, including surfactant structure and reorganization. For most (if not all) pulmonary diseases there is a dysregulation of host defense and inflammatory processes and/or surfactant dysfunction or deficiency. Because SP-A plays a role in both of these general processes where one or both may become aberrant in pulmonary disease, SP-A stands to be an important molecule in health and disease. In humans (unlike in rodents) SP-A is encoded by two genes (SFTPA1 and SFTPA2) and each has been identified with extensive genetic and epigenetic complexity. In this review, we focus on functional, structural, and regulatory differences between the two SP-A gene-specific products, SP-A1 and SP-A2, and among their corresponding variants. We discuss the differential impact of these variants on the surfactant structure, the alveolar microenvironment, the regulation of epithelial type II miRNome, the regulation and function of the AM, the overall survival of the organism after infection, and others. Although there have been a number of reviews on SP-A, this is the first review that provides such a comprehensive account of the differences between human SP-A1 and SP-A2.

Synthesis and evaluation of magnetic surfactants for high temperature oilfield application

Magnetic surfactants are a unique class of amphiphiles that can manage self-assembly in a controlled manner in the presence of the applied magnetic field. However, any surfactant for oilfield application must be soluble in water and exhibit high heat stability as it needs to stay in harsh reservoir conditions. Herein, we report a synthesis of two new magnetic surfactants that contain different hydrophobic moieties (ethoxylated alky tail and oleic tail). The chemical structures of the magnetic surfactants and their nonmagnetic parent surfactants were elucidated by ESI-MS, NMR (1H, 13C), and FTIR analysis. Both surfactants display good aqueous solubility due to the insertion of ethoxy units and unsaturation in the hydrophobic tail. The effect of hydrophobic tails on heat and surface/interface properties was investigated. Rendering to thermal gravimetric curves, the degradation temperature of magnetic surfactants was near 270 °C. This clearly showed that the magnetic surfactants contain high thermal stability for elevated temperature reservoirs. However, the effect of change of hydrophobic tail appears to be insignificant in thermal stability tests. An analysis of the surface tension showed that magnetic surfactants were more effective than corresponding nonmagnetic surfactants exhibiting higher surface tension (γ) reduction of water even with no magnetic field. Moreover, the magnetic surfactant containing an ethoxylated alkyl tail showed more surface tension (γ) reduction of water than a magnetic surfactant with an oleic tail. The research outcome on the synthesized magnetic surfactants makes them an attractive choice in a harsh oilfield environment. To the best of our knowledge, this is the first report on the magnetic surfactants that can toleratate high temperature reservoir conditions.

Treatment With Exogenous Lung Surfactant

The presented literature review examines the structure of the endogenous pulmonary surfactant, as well as the use of exogenous surfactant (Curosurf®) in various pathological conditions of the respiratory system. The endogenous lung surfactant is a lipoprotein complex that is synthesized by type II alveolar cells. It supports the breathing process and is a major component of the lung's immune defenses. In clinical practice, about 80% of premature infants develop respiratory distress syndrome (RDS). This condition requires intrabronchial administration of poractant alfa (Curosurf®), which results in reduced respiratory stress and increased survival. Apart from RDS, lung surfactants are also used in the treatment of asthma. Various mechanisms have been identified by which the surfactant is important for the pathophysiological course of the disease. Synthetic and natural surfactants that suppress the immune response can be used to treat asthma. For example, Alveofact®, Survanta® and Exosurf® lead to concentration-dependent suppression of lymphocyte function and proliferation, and Curosurf® also inhibits neutrophil activation. It also reduces the production of superoxide anions and the release of proinflammatory mediators from monocytes. Curosurf® is also relevant for Covid 19 associated pneumonia. It is believed that its intrabronchial administration will lead to improved blood oxygenation levels. Also, administration of surfactant would reduce pulmonary edema and improve the excessive inflammatory response found in autopsies of patients with COVID-19.

Enhancing the dispersibility of multiwalled carbon nanotubes within starch-based films by the use of ionic surfactants

The incorporation of carbon-based nanomaterials into biopolymer matrix, to provide mechanical reinforcement and to obtain electrically conductive bionanocomposites, requires the homogeneous dispersion of the fillers. Herein, it is investigated the influence of surfactant structures on the dispersibility of multiwalled carbon nanotubes (MWNT) within starch matrix. Three different ionic surfactants, sodium dodecyl sulphate (SDS), cetyltrimethylammonium bromide (CTAB) and sodium cholate (SC), are employed to disperse the MWNT. Films with MWNT-SC show better dispersibility and an increase of about 75% of tensile strength and 60% of Young's modulus compared with films using MWNT-SDS and MWNT-CTAB. Nevertheless, MWNT functionalized with CTAB impart the highest values of antioxidant activity (scavenging activity around 30% in 1.5 h) and electrical conductivity (σ =14.75 S/m) to starch matrix. The properties of starch-based films can be tailored according to the physical adsorption of each surfactant on MWNT surface and/or the interfacial interaction of the surfactant with starch chains.

The Role of Pulmonary Surfactant in COVID-19 Understanding

Background: In Covid-19 the virus infects the respiratory tract in human. When lung tissue becomes diseased, the walls and lining of the alveoli and capillaries are damaged. At this point lung compliance and ventilation decrease. Pulmonary surfactant that is produced and dispersed into alveolar space, has a significant role in understanding how heavily covid-19 interferes and infects lung cells. The importance of pulmonary surfactant in alveoli is to lower surface tension at air/liquid interface in the lung. This is achieved by reducing the work of breathing and preventing alveolar collapse. The main constituent of pulmonary surfactant is dipalmitoylphosphatidylcholine (DPPC) (C40H80NO8P). It is a phospholipid containing two non polar palmitic acid C16 chains as hydrophobic tails linked to a polar head group of a phosphatidylcholine (also known as lecithin).
 Rationale of the Review and Objective Method: When DPPC molecules are in contact with a polar solvent, micelles which grow further into bilayers are formed considering their cylindrical structures. This trait makes the whole structure of pulmonary surfactant as amphipathic and surface active molecules. The head group of phosphatidylcholine in the pulmonary surfactant is attracted by polar liquid molecules causing a reduction of the liquid surface tension.
 Conclusion: This review complements the quoted information analysing them theoretically and integrates recent advances in pulmonary surfactant research with the global pandemic.

Nonionic surfactant stabilized polytetrafluoroethylene dispersion: Effect of molecular structure and topology

Polytetrafluoroethylene (PTFE) is a kind of fluoropolymer with many critical applications. Nonionic surfactant stabilized concentrated PTFE aqueous dispersions are widely used to prepare corresponding products via dipping, spraying, spinning, or film casting, as these surfactants exert a negligible effect on the properties of the products. Although many nonionic surfactants have been used to stabilize PTFE dispersions in industry, the effects of molecular structure and topology are not well-documented; thus, currently, there is no basis for selecting or designing suitable novel surfactants to enhance dispersion stability. In this work, five nonionic surfactants with different topological structures including Tween 20, Tween 60, Tween 80, Brij L23, and Brij O20, were used to prepare concentrated PTFE dispersions. The variation of particle morphology before and after concentration was examined by scanning electron microscopy, and the static stability of the dispersions was quantitatively and objectively characterized using a Turbiscan analyzer based on multiple light scattering. Then the effect of surfactant molecular structure and topology on dispersion stability was discussed. We found that, after the enrichment process, the PTFE microspheres were tightly packed, and some were deformed. Brij surfactants which bears a linear hydrophilic oxyethylene (EO) chain can form a thicker hydration layer on the surface of PTFE particles than those of Tween surfactants which contains a branched hydrophilic EO chain. Accordingly, PTFE dispersions with Brij surfactants show better static stability. Moreover, in comparison with the saturated hydrophobic tail, the unsaturated hydrophobic chain is more flexible, so it can adhere to the surface of PTFE particles better, improving the stability. In addition, the increase of surfactant concentration contributes to the increase of micelles density and viscosity of the bulk dispersion, which can also enhance the stability. These findings are beneficial to design or choose suitable surfactants for high stability and high-quality concentrated PTFE dispersions.

Adsorption of Saponin Natural Surfactant on Carbonate Rock and Comparison to Synthetic Surfactants: An Enhanced Oil Recovery Prospective

Surfactant flooding is one technique of chemical enhanced oil recovery (EOR) aimed at improving the microscopic displacement efficiency of trapped residual oil via reducing the oil–water interfacial tension and wettability alteration. Success of surfactant flooding strongly relies on surfactant loss through its adsorption onto reservoir minerals to ensure maximum transfer to target reservoir. The current study examines the adsorption behavior of saponin natural surfactant onto carbonate rock outcrops. As an environmentally friendly extract from plants, saponins have shown the potential to increase oil recovery, although saponin loss or adsorption on surfaces is yet to be studied. Common synthetic surfactants of various types (i.e., cationic and anionic) and different molecular structures (other nonionic surfactants) have also been studied to provide comparisons to saponin. The surfactant adsorption onto carbonate samples was studied by batch adsorption experiments, with the residual surfactant concentration determined by the surface tension technique. It was found that saponin, a natural nonionic surfactant, adsorbed less than the ionic surfactants, since saponin adsorption is not governed by electrostatic interactions but weaker hydrogen bonding. Such data concludes that saponins are likely to yield less retention than the ionic surfactants, but compared to other nonionic surfactants its retention is greater. This is likely attributed to differing surfactant molecular structures. Due to its branch-like structure with more terminal functional groups, saponin adsorbs more on the rock surface compared to other long-chain nonionic surfactants. The findings of the current study provide a useful guide in surfactant selection for EOR and highlight a potential of natural and environmentally friendly surfactants.

Formulation Improvements in the Applications of Surfactant-Oil-Water Systems Using the HLDN Approach with Extended Surfactant Structure.

Soap applications for cleaning and personal care have been used for more than 4000 years, dating back to the pharaonic period, and have widely proliferated with the appearance of synthetic surfactants a century ago. Synthetic surfactants used to make macro-micro-nano-emulsions and foams are used in laundry and detergency, cosmetics and pharmaceuticals, food conditioning, emulsified paints, explosives, enhanced oil recovery, wastewater treatment, etc. The introduction of a multivariable approach such as the normalized hydrophilic–lipophilic deviation (HLD N) and of specific structures, tailored with an intramolecular extension to increase solubilization (the so-called extended surfactants), makes it possible to improve the results and performance in surfactant–oil–water systems and their applications. This article aims to present an up-to-date overview of extended surfactants. We first present an introduction regarding physicochemical formulation and its relationship with performance. The second part deals with the importance of HLD N to make a straightforward classification according to the type of surfactants and how formulation parameters can be used to understand the need for an extension of the molecule reach into the oil and water phases. Then, extended surfactant characteristics and strategies to increase performance are outlined. Finally, two specific applications, i.e., drilling fluids and crude oil dewatering, are described.

Effects of molecular structure of polymeric surfactant on its physico-chemical properties, percolation and enhanced oil recovery

Polymeric surfactant can simultaneously thicken aquous phase and reduce water–oil interfacial tension (IFT), which makes it present a great application prospect in the oilfield taword enhanced oil recovery (EOR). There are two kinds of polymeric surfactant with different molecular structures are commonly used to realize the salt resistance, thermal endurance and shear resistance. However, the influence of the molecular structure of polymeric surfactant on their properties related on EOR are not well understood. In the work, we synthesized two kinds of polymeric surfactants with different molecular structure which respectively named intermolecular association molecule (IAM) and rigid chain molecule (RCM). Their physico-chemical properties, porous media transportation and EOR are compared with a series of experiments. It is found that the hydrodynamic characteristic sizes and retention of IAM are higher than those of RCM via the membrane filtration test and nuclear magnetic resonance (NMR) scan. These features make IAM have a larger resistance factor and residual resistance factor than RCM and hydrolyzed polyacrylamide (HPAM) in the same viscosity. Compare to HPAM with shear thinning, RCM presents a Newtonian fluid region and IAM presents a shear thickening region when the shear rate is lower than 1 s−1. The spatial structure of IAM can pack oil drop into its network, which make it easy to form oil-in-water-in-oil (O/W/O) emulsions. Moreover, the concentration and water–oil ratio (WOR) rarely affect the stability of IAM emulsions once the intermolecular association generated. The increamental oil recovery factor of IAM is 17.5% after water flooding in the three-layer core flooding experiments with the permeability of 500 mD, 1500 mD and 3000 mD at 55℃, which is higher than that of 14.5% for RCM and 11.4% for HPAM.