Surfactant Molecular Structure Research Articles

Structure–property relationships of cationic polyurethane surfactants: Impact on surface activity and anticorrosion performance

Three cationic polyurethane surfactants (LC1–1, LC2–2, and LC2–3), each featuring different hydrophobic structures, were synthesized using isophorone diisocyanate, N-methyl diethanolamine, 1-bromohexadecane, and 1-bromobutane. The synthesized cationic polyurethane surfactants exhibited low surface tension, excellent foaming properties, and resistance to salt, attributed to steric hindrance among long-chain alkyl groups and their “multi-point anchoring” ability. The corrosion inhibition performance of polyurethane surfactants on carbon steel in 1 M HCl solution was evalutated, and LC2–2 showing a considerable corrosion inhibition efficiency of 97.0 %. This film effectively reduced/isolated contact between the corrosive solution and the steel interface. Furthermore, quantum chemical calculations corroborated the electrochemistry experiment results, affirming that the molecular structure of LC2–2 is particularly conducive to inhibiting the corrosion of carbon steel. This study explores the relationship between the molecular structure of surfactants and its impact on both surface activity and corrosion inhibition efficiency.

Systematically varying zwitterionic-siloxane surfactant structure to affect interfacial properties, foam stability, and fire suppression

Zwitterionic siloxane-sulfobetaine (siloxaneSB) surfactants are developed to replace per- and poly-fluoroalkyl substances (PFAS) used currently in aqueous firefighting foams because PFAS pose significant threats to environment and human health. SiloxaneSB surfactant's head and tail structures are varied gradually, one step at a time, to vary hydrophilicity of the head and hydrophobicity, and oleophobicity of the tail. Identical methods and conditions are used across all the surfactants to correlate surfactant structure to interfacial and foam properties, and fire suppression. The results suggest that the amphiphilic balance of the siloxane surfactant have dramatic effects on CMC, interfacial tension, foam expansion ratio, foam degradation, heptane vapor permeation through a foam layer, and fire suppression but little effect on bubble size, coarsening, and liquid drainage. They show synergism between siloxaneSB and alkylpolyglycoside in gasoline fire suppression while trisiloxane-polyoxyethylene exhibited synergism in heptane fire suppression. A 28 ft2 gasoline pool-fire suppression results were consistent with the bench-scale findings for tetrasiloxaneSB and trisiloxane-polyoxyethylene formulations. Small changes to surfactant molecular structure can dramatically improve its amphiphilic balance, synergisms, fuel-foam interactions resulting in improved effectiveness of fluorine-free foams but depend very much on the fuel, unlike the fluorocarbon surfactants.

Experimental and numerical modeling of a novel surfactant flooding: Core scale to reservoir models

This comprehensive study delves into an application of surfactant flooding as a robust enhanced oil recovery (EOR) technique, incorporating both core-scale experiments and reservoir-scale numerical simulations. The research's focal point is to evaluate a novel surfactant's performance in extending oil recovery efficiency within an oil reservoir. The study commences with thorough laboratory experiments at the core scale, illuminating the interplay of fluids within porous media. Transitioning seamlessly to reservoir-scale numerical modeling, the research replicates real-world reservoir conditions. Various well configurations are scrutinized to optimize surfactant flooding strategies for EOR purposes. A key aspect of this analysis is the in-depth examination of the sensitivity of numerical simulations to changes in relative permeability curves during surfactant injection, enabling a robust assessment of the performance of surfactant injection in a broad spectrum of uncertainties. Comparative experiments elucidated the significant influence of a surfactant molecular structure, with aliphatic variants showcasing superior oil displacement efficiency. Moreover, combining surfactant and polymer proved pivotal, enhancing reservoir sweep efficiency and significantly boosting oil recovery. This work establishes a comprehensive framework for evaluating chemical flooding, including surfactant and polymer, as a potent EOR method by bridging the gap between core-scale experiments and reservoir-scale simulations.

Wormlike micellar solutions formed by an anionic surfactant and a cationic surfactant with two head groups.

Innovation in the molecular structure of surfactants is important for the preparation of soft materials with novel properties. In this study, we synthesized a cationic surfactant, N1,N1,N1,N1,N3,N3,N3-pentamethyl-N3-(3-stearamidopropyl)propane-1,3-diammonium bromide, hereafter referred to as C18-DQA. Unlike conventional cationic surfactants, C18-DQA contains two quaternary ammonium head groups and a long-saturated alkyl chain equal to a chain length of 21 carbon atoms. C18-DQA exhibits a low Krafft point of ∼0 °C and a water solubility >1000 mM at 25 °C. The critical micelle concentration (cmc) of C18-DQA was determined to be 0.59 mM using the Nile red method. C18-DQA was mixed with sodium laurate (SL) at different molar ratios to produce transparent solutions with excellent viscoelasticity over a wide concentration range. The 1 : 1.5 molar ratio C18-DQA/SL mixed solutions exhibited gel-like behavior for a total surfactant concentration of 2.88 wt% (75 mM). The solution with a total surfactant concentration of 300 mM (120 mM C18-DQA and 180 mM SL) achieved a maximum zero-shear viscosity (η0) of 4224 Pa s. Cryogenic transmission electron microscopy analysis revealed the formation of extremely long wormlike micelles, with a cross-sectional diameter of 5 nm and contour length >3 μm, in the mixed solutions. C18-DQA and SL molecules were drawn close by electrostatic attractions, leading to a suitable molecular geometry for the extensive growth of wormlike micelles. This work will act as an important reference for the future preparation of highly viscoelastic solutions by mixing cationic and anionic surfactants. The proposed system is also expected to have potential applications in cosmetic formulations, home care products, and oilfield fracturing fluids.

Evaluation of the interfacial elasticity of surfactant monolayer at the CO2–water interface by molecular dynamics simulation: Screening surfactants to enhance the CO2 foam stability

Foam stability is adversely affected by the drainage process in the liquid film, which has been a great challenge for CO2 foam flooding in applications. The Gibbs-Marangoni effect, which is induced by the interfacial tension (IFT) gradient, provides a resisting force to the thinning of liquid films in foams under disturbance. Surfactants with higher interfacial elasticity enable rapid recovery to the equilibrium state, thereby improving the stability of the CO2 foam film. However, there is a lack of mechanistic studies aimed at elucidating the correlation between the interfacial elasticity of surfactant monolayers and the molecular structure of surfactants. In this paper, molecular dynamics simulations were employed to investigate the impact of the headgroups and linking groups of sodium polyoxyethylene alkyl ether sulfate (AES), sodium dodecylbenzene sulfonate (SDBS), sodium dodecyl sulfate (SDS), sodium dodecyl sulfonate (SDSn), and sodium laurate (SLA) surfactants on the interfacial morphology, monolayer properties, and surfactant behaviors at the CO2–water interface under reservoir conditions. The results show that the capacity to enhance CO2 foam stability follows the order AES > SDS > SDSn > SDBS > SLA, which is in good agreement with the available experiments. AES monolayers can reach the lowest IFT (∼0.2 mN/m) and the highest interfacial elasticity (30.4 mN/m). We show that the ethylene oxide groups (EO chains) can strongly interact with water molecules via hydrogen bonding and have affinity interactions with CO2 molecules, which is beneficial to the hydrophilic-CO2-philic balance (HCB). SDS monolayers show the second-lowest IFT (3.1 mN/m) and second-highest interfacial elasticity (26.0 mN/m). The linking oxygen atom in SDS facilitates bond rotation and is favorable to film stability. The phenyl group makes SDBS molecules too rigid and has poor HCB, leading to low stability with high IFT (16.0 mN/m) and low interfacial elasticity (13.1 mN/m). SLA has the highest IFT (22.1 mN/m) and lowest interfacial elasticity (6.3 mN/m), and also presents strong aggregation behaviors at the interface owing to interactions between the carboxyl groups. The simulation method and the microscopic insights delivered here are of great significance in screening surfactants to improve CO2 foam performance in oilfields.

Microemulsions Based on Diverse Surfactant Molecular Structure: Comparative Analysis and Mechanistic Study

Microemulsion flooding technology, known for significantly reducing interfacial tension, improving rock wettability, and providing strong driving forces at the microscopic level, has been widely applied in enhancing oil recovery in oil fields. This article summarizes the relevant literature and introduces the classification, formation mechanisms, research models, and factors affecting the performance of microemulsions. Particularly, it conducts a comparative analysis of microemulsion systems formed by surfactant molecules of different structures, aiming to provide new perspectives for the study of surfactant molecular structures and to further optimize the performance of microemulsion systems. The study finds that modifying surfactant molecules by adding benzene rings, increasing the length of hydrophobic tails, and enlarging hydrophilic heads can significantly increase the volume of the middle phase, exceeding 30%. These findings provide important guidance for optimizing microemulsion systems.

Analyzing the flotation kinetics of long-flame coal slurry using water-soluble emulsified collector mixtures

This article investigates the variations in flotation responses of long-flame coal using emulsified collector mixtures, utilizing various flotation kinetic (FK) models for analysis. The fitting process was carried out using the Origin software. The Fourier transform infrared spectroscopy (FTIR) results indicated that as the number of adjacent H atoms increased, the absorption peak on the surface of long-flame coal, processed by various emulsified collector mixtures, gradually shifted towards short-wave numbers. Moreover, the X-ray photoelectron spectroscopy (XPS) results suggested that COC/COH groups on the coal surface could form hydrogen bonds with oxygen-containing functional groups (OCFGs) in the surfactant molecular structure. Furthermore, the hydrophobic groups of the benzene ring in 4-dodecyl phenol (4-DDP) could adsorb onto the coal surfaces through π-π bonds, enhancing the surface hydrophobicity of long-flame coal. Moreover, the flotation performance of long-flame coal was significantly improved using the emulsified mixture of kerosene and 4-DDP, achieving a peak recovery of 39.86 %. The second-order model with a rectangular distribution of floatability led to an excellent fitting to the flotation process of long-flame coal when employing the emulsified mixtures.

Surfactant mediated silver synthesis: Influence of surfactant molecular structure on the size and shape of silver particles

The current work employs non-ionic surfactants polyethylene glycol tert-octylphenyl ether (Triton X-114) and polyoxyethylene (20) sorbitan monolaurate (Tween 20) as capping agents for synthesizing silver particles. Formation of icosahedrons and Wulff polyhedrons are thermodynamically preferable for FCC silver, and anisotropic morphologies such as triangular/hexagonal platelets are less likely. Yet, with the use of Triton X-114, appreciable quantity of platelets is obtained. Beyond the molar ratio of 2.5 (Triton X-114: AgNO3), only anisotropic particles are identified. It is believed that preferential adsorption of the surfactant inhibits crystal growth along 〈111〉 direction. Instead, the particles grow along the edges of the hexagonal/triangular plates. In contrast, the use of Tween 20 yielded silver (nano)particles with spherical shape. The presence of multiple polymeric chains in the Tween 20 molecule exhibits strong interaction with the silver particles by restricting growth along multiple facets. These observations indicate the significant role of the molecular structure of capping agents in determining particle size and morphology.

Multiheaded Cationic Surfactants with Dedicated Functionalities: Design, Synthetic Strategies, Self-Assembly and Performance.

Contemporary research concerning surfactant science and technology comprises a variety of requirements relating to the design of surfactant structures with widely varying architectures to achieve physicochemical properties and dedicated functionality. Such approaches are necessary to make them applicable to modern technologies, such as nanostructure engineering, surface structurization or fine chemicals, e.g., magnetic surfactants, biocidal agents, capping and stabilizing reagents or reactive agents at interfaces. Even slight modifications of a surfactant's molecular structure with respect to the conventional single-head-single-tail design allow for various custom-designed products. Among them, multicharge structures are the most intriguing. Their preparation requires specific synthetic routes that enable both main amphiphilic compound synthesis using appropriate step-by-step reaction strategies or coupling approaches as well as further derivatization toward specific features such as magnetic properties. Some of the most challenging aspects of multicharge cationic surfactants relate to their use at different interfaces for stable nanostructures formation, applying capping effects or complexation with polyelectrolytes. Multiheaded cationic surfactants exhibit strong antimicrobial and antiviral activity, allowing them to be implemented in various biomedical fields, especially biofilm prevention and eradication. Therefore, recent advances in synthetic strategies for multiheaded cationic surfactants, their self-aggregation and performance are scrutinized in this up-to-date review, emphasizing their applications in different fields such as building blocks in nanostructure engineering and their use as fine chemicals.

A novel surfactant material for performance enhancement on nucleate pool boiling heat transfer

Long-chain surfactants have been extensively studied for boiling enhancement, while the investigation of steroid surfactants is limited. In this study, steroidal bile salts were experimentally attempted for nucleate pool boiling enhancement on flat copper surface. Four types of bile salts were found effective in improving heat transfer coefficient (HTC) in aqueous form, with SDC having the most significant effect, followed by SHDC, SC, and STGC. The STGC deposited surface exhibited a simultaneous improvement of critical heat flux (CHF) and HTC with long-term repeatability. The enhancement mechanism is discussed by means of solution properties, bubble behaviors and surfactant molecular structure. Both aqueous and deposited bile salts show considerable boiling performance with existing materials, with better safety characteristics. The findings of this study can provide a bio-friendly approach to surfactant-aided energy conversion applications and contribute to the development of new-generation green surfactant materials.

Assessment of droplet self-shaping and crystallization during temperature fluctuations exceeding the melting temperature of the dispersed phase

Oil-in-water emulsions with crystalline dispersed phase are widely used formulations in life sciences. Ideally, during cooling each droplet crystallizes in its original size and shape set by chosen process parameters. Recently it was shown, that droplets may spontaneously break their shape symmetry crystallizing in non-spherical shape, which strongly depends on the surfactant molecular structure and cooling profile. In this contribution, we focus on the assessment of droplet self-shaping, crystallization and melting behavior during repeated cooling and heating cycles, and the influence of small changes in the temperature-time profile on these processes. These temperature cycles are typical conditions to which crystalline dispersions are subjected during storage and transport. Shape changes and crystallization of n-hexadecane droplets stabilized with the surfactants Brij® S20 and Tween® 60 were investigated by means of a thermo-optical method. In both model systems, self-shaping was observed during the first cooling cycle. Subsequent melting of particles led to the breakup of droplets into smaller, sub-micrometer droplets due to self-emulsification. When a second cooling step followed directly after melting at 20 and 22 °C, spontaneous self-shaping was again observed for n-hexadecane droplets stabilized with Brij® S20, while droplets stabilized with Tween® 60 crystallized in spherical shape. However, these samples showed self-shaping of droplets, when given longer times at 22 °C (incubation of 1 h) or being heated to the bulk Tween® 60 melting temperature (∼ 24 °C) before the second cooling step. During cooling of pure 1 wt% Tween® 60 solutions, crystal precipitation was observed to a great extent. Thus, the concentration of free surfactant molecules drops and may be too low to induce self-shaping of droplets. In 1 wt% Brij® S20 solutions, crystal precipitation was much less pronounced, probably leaving enough free molecules to induce self-shaping. In the case of Tween® 60, enough time after reheating and/or a high enough temperature is needed to melt the surfactant crystal precipitates and re-disperse the molecules to provide enough surfactants at the oil-water-interface for self-shaping during the second cooling scan. These results show, that the droplet crystallization and self-shaping behavior can greatly vary between different formulations, even when the surfactants are very similar in their molecular structure. Additionally, small changes in the temperature-time profile in the formulations’ lifetime have a distinctive influence on resulting particle size and morphology. The melting behavior of the dispersed phase, and crystallization and melting events of surfactants may have a distinctive influence on the particle size and morphology, and thus dispersion characteristics.

Forecasting the cloud point of alkoxylated nonionic surfactants

AbstractThe highest effectiveness of detergency for nonionic surfactants is observed in the proximity of the cloud point. This phenomenon is primarily influenced by surfactant molecular structure, such as carbon chain length and type of the hydrophilic components. Target of this investigation is to identify a relationship between the cloud point and the structure of nonionic surfactants based on ethoxylated (CnEm), ethoxylated‐propoxylated (CnEmPp) and propoxylated‐ethoxylated (CnPpEm) fatty alcohols. Three hundred and fifty nonionic surfactants have been prepared for this purpose. These surfactants differ in the C‐chain lengths, C4/C6 to C20/C22, and the amount of ethylene oxide (EO range [n] 2–22 ethoxylation) and propylene oxide (PO range [p] 0–12 propoxylation) moieties. Mapping the differences in the performance allows us to propose a high‐accuracy topological model describing the structure influence on the cloud point.

Surfactant-mediated electrodeposition of a pseudocapacitive manganese dioxide a twofer

Electrochemical energy storage is one of the most promising ways of storing energy from intermittent, renewable sources. To meet the needs, the development of scalable, earth-abundant, chemically stable, and environmentally friendly electrode materials is crucial. This work presents four cationic surfactant-mediated manganese sulfate electrolytic solutions used for the synthesis of electrolytic manganese dioxide (EMD) to produce scalable material that satisfies the pre-requisites desired for supercapacitor applications. The influence of the surfactant molecular structure, its concentration, and its interaction in the electrolytic sulfate bath was studied, which opens up new possibilities for the fabrication of the supercapacitor electrode. The performance of three surfactants (Tetradecyltrimethylammonium bromide, Didodecyldimethylammonium bromide, Benzyldodecyldimethylammonium bromide) was benchmarked against the widely used Cetyltrimethylammonium bromide under identical conditions. The surfactants were chosen based on their different head groups and hydrocarbon chains. Benzyldodecyldimethylammonium bromide-assisted EMD (EMD/B-AB) in a single-electrode device showed improved capacitance of 602 F g−1 (at 1 mA cm−2) over the other surfactant-mediated samples. The molecular dynamics simulations indicated that the electrodeposition of manganese dioxide is highly influenced by B-AB, as it adsorbs with the aryl group planar to the Pb surface. The appropriate concentration of B-AB surfactant in the bulk solution appears to be incorporated into the EMD deposit due to their hydrophobic nature and controlled nucleation and established improved pseudocapacitive performance to score a twofer. The asymmetric capacitor of EMD/B-AB30 vs. porous activated carbon exhibited a high specific capacitance of 91 F g−1, with an energy density of 32.4 Wh kg−1 for a corresponding power density of 971 W kg−1.

Bioinspired superwettability: From interfacial materials to chemistry

<p indent="0mm">Interfacial wettability is one of the fundamental problems in material science. The research on wettability regulation is of great significance in exploring new knowledge and creating new applications. Learning from nature, Prof. Jiang has summarized three basic principles of superwettability: (1) The static wetting is determined by the cooperative effect of nanostructure and surface energy; (2) the transition point of the superlyophilicity and superlyophobicity on the nanostructure is the lyophilicity-lyophobicity limitation; (3) the direction of liquid transport is regulated by chemical composition gradient, rough gradient, curvature gradient, etc. Based on these principles, he further extended the superwettability interfacial material systems to interfacial chemistry. He established a superwetting interfacial material system including 64 combinations, and expanded to various liquid systems with different pressure and temperature ranges, leading and promoting the global development of this field. In this paper, we will introduce the design of superwetting interface and the new law of liquid/gas/solid three-phase interfacial wettability. Based upon the new law of three-phase interfacial wettability, we state the application of water-oil separation, pesticide spraying, electrochemical sensors, and photoelectric material patterning. And the recent research and application prospect in the field of quantum-confined superfluid are discussed. In the part of water-oil separation, focusing on the key issue of constructing membrane materials with both fine pore structure and super-wetting properties, without changing the traditional separation membrane preparation process, the micro-nano multi-level structure of the membrane surface is constructed through structure-induced tuning, and the surface is chemically modified. Synergistic action is used to realize the regulation of membrane transport behavior of water droplets or oil droplets, and a series of novel structural membrane separation materials have been successfully prepared, realizing high-precision and high-throughput separation of oil-water emulsions under low driving pressure. In-depth research on the relationship between the molecular structure of surfactants and the kinetic behavior and thermodynamic state of droplets on specially wetted surfaces has led to the discovery of a very cheap anionic surfactant (sulfosuccinic acid) capable of forming vesicles. Sodium dioctyl ester (AOT) can inhibit the ejection and sputtering of pesticide droplets on the surface of superhydrophobic plants at a very low concentration (3/1000 mass concentration). Aiming at the historical problem of “deficient oxygen” during the use of electrochemical enzyme sensors, we proposed and constructed an oxygen-enriched enzyme electrode with solid/liquid/gas three-phase coexistence. The three-phase electrode will greatly improve the detection performance of existing sensors, has extremely broad application prospects in future disease monitoring, and provides a new design idea for the development of high-efficiency enzyme sensors. We exploit the principle of “liquid bridge confinement assembly” by inducing site-specific condensation and crystallization of small organic molecules by exploiting asymmetric wettability interfaces, fabricating one-dimensional arrays of organic polymer semiconductors by exploiting highly adhesive three-phase interfaces, and exploiting superwetting The micro-nano interface controls the three-dimensional dewetting process and realizes the preparation of highly oriented one-dimensional single-crystal nanowires. These three methods are the key issues to realize one-dimensional micro-nano materials from material preparation to device application. Since 2008, we have successfully achieved the fabrication of smart nanopores that mimic ion channels in biomembranes. This channel has properties similar to biological ion channel switching, selection and rectification. Furthermore, by imitating the mechanism of energy conversion in living systems, the design of energy conversion systems driven by chemical potential gradients based on biomimetic nanopores and the design of nanopore-based sensing devices are realized. Since 2018, we focused on dynamic superwetting. The concept of ionic/molecular superfluid is proposed, which promotes the understanding of the realization of ultra-low energy conversion and information transmission in biological systems and provides new ideas for the study of ultra-low energy chemical synthesis in biological systems. It is believed that future research on ionic/molecular superfluidity will promote the development of neuroscience and brain science, develop quantum ion technology, develop future chemical and chemical reactors with high flux, high selectivity and low energy consumption, and will produce a series of disruptive technologies.

Droplet splash and spread on superhydrophobic lotus leaves: Direct regulation by tuning the chain length of surfactant

Impact and spread of droplet on superhydrophobic surface are ubiquitous in inkjet printing, pesticide spraying, paint coating, and other fields. However, due to the extremely water-repellent properties of superhydrophobic surface, droplets frequently splash or roll off, causing great waste and serious environmental problems. Thus, searching for an effective strategy to regulate the droplet splash and spread on superhydrophobic surfaces is of remarkable significance. To address the above issues, herein, we demonstrate the controllable regulation on superhydrophobic lotus leaf surface by tuning the double-chain length of surfactants. The outcomes indicate different regularities for droplet splash in a short time (~10 ms) and spread in a relatively long period (~100 s). It can be concluded that dynamic surface tension of surfactant, diffusion rate of surfactant from the bulk to the interface, and assembly disaggregation rate dominate the impact process, whereas the adsorption kinetic and effectiveness of surfactant along with the spreading driving force determine the wetting transition. Surfactant owning suitable hydrophilic and hydrophobic ratio, fast diffusion rate, and unstable assembly could inhibit droplet splash and improve spreading pronouncedly, thereby enhancing the droplet deposition on superhydrophobic surfaces. This study makes original contribution to screen suitable surfactants from the structural aspects, especially double-chain length, which has not been treated in much detail to date. Our work not only creates a big impetus in illuminating the mechanism of surfactant molecular structure on droplet deposition processes but also greatly expands the applications of surfactant in many fields.

Predicting the aggregation number of cationic surfactants based on ANN-QSAR modeling approaches: understanding the impact of molecular descriptors on aggregation numbers.

In this work, a quantitative structure-activity relationship (QSAR) study is performed on some cationic surfactants to evaluate the relationship between the molecular structures of the compounds with their aggregation numbers (AGGNs) in aqueous solution at 25 °C. An artificial neural network (ANN) model is combined with the QSAR study to predict the aggregation number of the surfactants. In the ANN analysis, four out of more than 3000 molecular descriptors were used as input variables, and the complete set of 41 cationic surfactants was randomly divided into a training set of 29, a test set of 6, and a validation set of 6 molecules. After that, a multiple linear regression (MLR) analysis was utilized to build a linear model using the same descriptors and the results were compared statistically with those of the ANN analysis. The square of the correlation coefficient (R 2) and root mean square error (RMSE) of the ANN and MLR models (for the whole data set) were 0.9392, 7.84, and 0.5010, 22.52, respectively. The results of the comparison revealed the efficiency of ANN in detecting a correlation between the molecular structure of surfactants and their AGGN values with a high predictive power due to the non-linearity in the studied data. Based on the ANN algorithm, the relative importance of the selected descriptors was computed and arranged in the following descending order: H-047 > ESpm12x > JGI6> Mor20p. Then, the QSAR data was interpreted and the impact of each descriptor on the AGGNs of the molecules were thoroughly discussed. The results showed there is a correlation between each selected descriptor and the AGGN values of the surfactants.

Comparison of influence of surfactants on thermokinetic characteristics of alkali-activated slag cement

Increasing the durability of concrete and reinforced concrete structures according to the criterion of crack resistance is a relevant task of construction materials science. To solve this task, this paper proposes effective solutions for adjusting thermofinite characteristics of alkali-activated slag cement (ASC) by using surfactants of various chemical nature in order to control the thermally-stressed state of concrete based on it (ASC concrete). The method of calorimetry was applied to show that the problematic issue is to adjust the structure formation of ASC by anion-active surface-active substances based on complex polyesters. This is predetermined by the instability of the molecular structure of surfactants in the hydration environment of ASC due to the destruction of complex ester bonds as a result of alkaline hydrolysis. Thermokinetic analysis has demonstrated the effectiveness of using anion-active surfactants, which do not contain ester bonds, as regulators of crack resistance of ASC concrete. Simple polyesters and multi-atom alcohols provide the ability to adjust the duration of the induction period while ensuring the required completeness of ASC hydration within a time frame. The effectiveness of cation-active surface-active substances has been shown, which are characterized by the stability of the molecular structure in the hydration environment of ASC and an increased level of adsorbing capacity. The decrease in the effectiveness of surface-active substances has been shown, in terms of the effect on the heat release of ASC, in the following series: alkaline salt of carboxylic acid&gt;salt of the quaternary ammonium compound&gt;simple polyester&gt; polyalcohol&gt;complex polyester. The reported results are important in view of the possibility of effective adjustment of ASC heat release by influencing the structure formation of surfactant with a certain molecular arrangement in order to predictably reduce crack formation in a thermally-stressed state and a corresponding increase in the durability of structures

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.

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.