Aggregation Behavior Of Surfactants Research Articles

Effect of Hydrophilic Function Groups on the Properties of Short‐Chain Fluorocarbon Surfactants

AbstractShort‐chain fluorocarbon surfactants grafted with alcohol, carboxyl and ester functional groups were prepared by quaternization with short‐chain perfluorobutyl sulfonyl fluoride as raw material. The structures of surfactants were characterized by infrared spectroscopy, nuclear magnetic resonance and mass spectrum. The surface activity, micelle formation process and micelle aggregation behavior of surfactants were studied by surface tensiometer, dynamic light scattering particle size analyzer and fluorescent spectrophotometer. The results show that the critical micelle concentration (CMC) of surfactants are 19.3, 7.8 and 2.2 mmol L−1, and the surface tension of the surfactant solution at CMC are as low as 17.3, 19.2 and 18.5 mN m−1, respectively. The standard Gibbs free energy ( ) values of surfactants are negative, and the absolute values of are less than the standard Gibbs adsorption energy ( ), illustrating that the adsorption process is easier than the micelle formation process. In addition, the size distribution of the aggregates is much larger than that of spherical micelles, showing that the surfactant self‐assembled into larger aggregates in solution. The grafted hydrophilic functional groups show a significant effect on the performance of surfactants. The ester‐based surfactant has a lower CMC value, which has the advantages of small dosage, good economy and excellent application value.

The impact of chelating agent pH on the stability and viscosity of CO2 foam under harsh reservoir conditions

The injection of CO2 foam into the carbonate reservoir for enhanced oil recovery (EOR) has attracted special interest in the last decades; nevertheless, the understanding of the effect of liquid solution chemistry on foam stability at high temperatures and salinities is limited. Hence, this paper fully investigates the effect of chelating agents L-glutamic acid-N, N-diacetic acid (GLDA) pH, and hydrochloric acid (HCl) on the stability and viscosity of generated CO2 foam for heterogeneous carbonate formation under reservoir conditions. In this paper, Duomeen TTM and Armovis VES surfactants were utilized due to their capabilities to produce viscous CO2 foam under harsh conditions. The foamability, foam stability, and foam structure were studied at 100 °C and 1000 psi using a high-temperature and high-pressure (HPHT) foam analyzer. The measurement of CO2 foam viscosity was determined at 100 °C, 1000 psi, and 70 % foam quality using the HPHT foam rheometer. Rheology experiments and dynamic light scattering investigated the micelle’s size or aggregation behavior of surfactants. The obtained results showed that the Duomeen TTM generated unstable foam; however, foam stability and foamability improved with the decrease in GLDA pH. Armovis VES showed excellent CO2 foam performance, where the foam half-life time of Armovis VES systems was 240 min. The liquid drainage and bubble coarsening were delayed due to the formation of the viscoelastic liquid phase. The foamability of Armovis VES was improved as the GLDA pH decreased. Furthermore, the addition of HCl to Armovis VES solution presented the highest foamability. The outcomes of the HPHT foam analyzer and HPHT viscometer proved that as the pH of Armovis VES solution decreased, higher foamability was produced. The highest foam viscosity was obtained using the synergic effect of 0.5 wt% Duomeen TTM and 0.5 wt% Armovis VES (39 cp at 100/s). In comparison, 1 wt% Armovis VES presented the lowest foam viscosity (30 cp at 100/s). The outcomes of this research can provide insight into the effect of chemistry on CO2 foam and extend its application in oilfield development. This work broadens the design of novel CO2 foam formulation, leading to the improvement of sweep efficiency in CO2-EOR methods and enhance the gas trapping in carbon storage.

Study of Interfacial Properties of Anionic–Nonionic Surfactants Based on Succinic Acid Derivatives via Molecular Dynamics Simulations and the IGMH Method

Surfactants are widely used in fields such as oil recovery and flotation. The properties and mechanisms of surfactants can be effectively studied using molecular dynamics (MD) simulations. Herein, the aggregation behavior of surfactants was studied at the oil–water interface by MD simulation, and the micro-morphology of surfactants was analyzed under a low concentration and saturated state at the oil–water interface, respectively. The visualization results of the MD simulation showed that DTOA was saturated at the oil–water interface at 120 surfactant molecules, whereas 160 surfactant molecules were required for BEMA. In addition, the effect of surfactant concentration on the interfacial thickness and hydrogen bond distribution was studied, with the inflection point of hydrogen bond distribution identified as a characteristic parameter for surfactant saturation at the oil–water interface. The aggregation behavior of their hydrophobic and hydrophilic chains at the oil–water interface was qualitatively assessed using order parameters. Finally, the aggregation state of surfactants in salt-containing systems was studied, and it was found that the surfactants could effectively adsorb magnesium ions and calcium ions at the oil–water interface. However, the curve of the number of hydrogen bonds varies greatly, with a possible reason being that BEMA has a different coordination manner with diverse metal ions. This study provides some original insights into both the theoretical study and practical application of anionic and nonionic surfactants.

Fluorescence lifetime of pyrene butyric acid as a versatile sensing tool for monitoring self-assembled systems and microenvironment

Sensing applicability of the fluorescence lifetime of pyrene butyric acid (PBA) to understand the aggregation behaviour and microheterogeneity of different charged self-assembled surfactants i.e., anionic (sodium dodecyl sulfate, ∼ 8.5 mM), cationic (Cetyltrimethylammonium bromide, ∼ 0.95 mM), and non-ionic (Triton X100, ∼ 0.27 mM) in aqueous solution is explored in this study. Time domain fluorescence decay of PBA is introduced for the first time as a sensitive tool for characterizing the molecular microenvironment and for predicting the aggregation behaviour of surfactants, including the monitoring low to higher-order aggregates. A non-extensive distribution analysis on the fluorescence decay profiles yields the fluorescence lifetime and Full Width at Half Maxima (FWHM), with the latter serving as an indicator of the heterogeneity of the molecular microenvironment of the 'fluoroprobe'.The analytical strength of the fluorescence lifetime of PBA as a sensing tool has been validated using biosurfactants sodium cholate (NaC) and sodium deoxycholate (NaDC) with high fidelity. Careful analysis of the non-extensive distribution of the lifetime of PBA displays a substantial sensitivity towards microheterogeneity in its immediate vicinity and hence monitors the higher-order aggregation behaviour of bile salts in aqueous medium.

Tribological performance of a surfactant derived from its structure of molecular aggregates in water

Surfactants are promising additives for water-based lubricant surfaces due to their ability to adsorb on metal surfaces and reduce friction under boundary lubrication. In this study, the aggregation behavior of surfactants in aqueous solutions and their effects on friction and anti-wear properties were investigated using sodium 2-hexyldecanoate (2HDNa) as an example. The results revealed that 2HDNa forms vesicles at low concentrations and transits to micelles at higher concentrations. The presence of vesicles led to a significant reduction in friction coefficient and improved anti-wear properties by forming an absorbed film, which was confirmed by neutron reflectometry (NR). The findings of this study emphasize the lubrication and anti-wear performance of vesicles and the importance of surfactant concentration control in water-based lubrication.

Molecular Mechanism Study on the Effect of Microstructural Differences of Octylphenol Polyoxyethylene Ether (OPEO) Surfactants on the Wettability of Anthracite.

Inhalable coal dust poses a serious threat to coal mining safety, air quality, and the health of miners. Therefore, the development of efficient dust suppressants is crucial for addressing this issue. This study evaluated the ability of three high-surface-active OPEO-type nonionic surfactants (OP4, OP9, and OP13) to improve the wetting properties of anthracite via extensive experiments and a molecular simulation and determined the micro-mechanism of different wetting properties. The surface tension results show that OP4 has the lowest surface tension (27.182 mN/m). Contact angle tests and wetting kinetics models suggest that OP4 exhibits the strongest wetting improvement ability on raw coal with the smallest contact angle (20.1°) and the fastest wetting rate. In addition, FTIR and XPS experimental results also reveal that OP4-treated coal surfaces introduce the most hydrophilic elements and groups. UV spectroscopy testing shows that OP4 has the highest adsorption capacity on the coal surface, reaching 133.45 mg/g. The surfactant is adsorbed on the surface and pores of anthracite, while the strong adsorption ability of OP4 results in the least amount of N2 adsorption (8.408 cm3/g) but the largest specific surface area (1.673 m2/g). In addition, the filling behavior and aggregation behavior of surfactants on the anthracite coal surface were observed using SEM. The MD simulation results indicate that OPEO reagents with overly long hydrophilic chains would produce spatial effects on the coal surface. Under the influence of the π-π interaction between the hydrophobic benzene ring and the coal surface, OPEO reagents with fewer ethylene oxide quantities are more prone to adsorb onto the coal surface. Therefore, after the adsorption of OP4, both the polarity and the water molecule adhesion ability of the coal surface are greatly enhanced, which helps to suppress dust production. These results provide important references and a foundation for future designs of efficient compound dust suppressant systems.

Application of aggregation behavior of nonionic surfactants to develop a smart detergent for washing fruits with emphasis on pesticide residues removal

AbstractModel smart detergents for fruit washing were designed. Their physicochemical and functional properties were determined, with particular emphasis on the efficiency of removing pesticide residues. The specific behavior of nonionic surfactants near the so‐called cloud point was used in the design of the new smart detergent. The high performance of detergents was related to the temperature‐dependent aggregation behavior of surfactants. Liquid chromatography coupled with mass spectrometry (LC–MS/MS) was used to evaluate the washing efficiency. Four types of pesticides (boscalid, acetamiprid, pyraclostrobin and pendimethalin) were applied to apples and then washed with designed detergents. Washing efficiency was evaluated based on the change in pesticide content on the apple surface. Compared to water, the model detergents were found to be more effective in removing pesticide residues, reaching values above 80%. The detergents were also evaluated for skin effects and revealed a low potential for skin irritation.

Study of Solvation Behavior Thermodynamics and FT-IR Spectroscopic Analysis of N-Butylethanolammonium Based Ionic Liquids with Polar Solvents

The effect of anion geometry on aggregation behavior of surfactant with aqueous solutions was investigated by the systematic measurements of concentration, temperature dependent density and derived thermodynamic properties. In this work, N-Butylethanolammonium trifluoroacetate [BEATFA] and N-Butylethanolammonium nitrate [BEAN] ionic liquids (ILs) were synthesized and characterized by 1H NMR. The binary systems IL+water/ethanol were prepared for the concentration ranges from 0.0264 to 0.4621 mol·kg−1 and the temperature ranges from 298.15 K to 318.15 K. Further, the apparent molar volume (Vɸ), partial molar volume (Vɸ∞), thermal expansion coefficient (α) and apparent molar expansivity (Eɸ) were derived from the experimentally measured density data. The critical aggregation concentration (cac), apparent molar volume at critical aggregation concentration (Vɸ,CAC), apparent molar volume in aggregation phase (Vɸ,mic), change in apparent molar volume due to aggregation (∆Vɸ,m) and degree of ionization (α′) were derived from the plot of apparent molar volume versus inverse of ILs concentration. The thermodynamic aggregation properties such as standard Gibb's free energy of micellization (∆Gom), standard enthalpy of micellization (∆Hom) and standard entropy of micellization (∆Som) were calculated from experimental measurements. The sign and magnitude of apparent molar volume at infinity dilution reveals about IL+solvent or IL-IL interactions between the component molecules. The system [BEAN]+water showed lowest positive magnitude in both Vɸ∞ and cac than compare to [BEATFA]+water due to the formation of stronger IL+solvent intermolecular interactions through the H-bonding. The variance in observed Vɸ∞ and cac data with different solvents due to the solvophobic effect and hydrogen bonding tendency was explained by FT-IR spectroscopy and DFT computational study. Among the all binary systems, [BEAN]+water showed highest intermolecular interaction tendency than other systems, the obtained results were compared with available literature data and analyzed in terms of intra and intermolecular interactions, polarity of solvents, hydrophobicity, nature anion, size and shape of the anion.

Construction of photoresponsive azobenzene-decorated cationic surfactant-based self-assembled vesicles and controlled drug release

Surfactant aggregates possess a unique feature of space partitioning, and hence are widely used as drug carriers. A comprehensive understanding of the regulation of surfactant aggregation behavior can achieve the controlled release of drugs. In this work, the surface activity and photoisomerization behavior of the synthetically prepared azobenzene-functionalized cationic surfactant (AzoNC8) were thoroughly studied by analyzing the surface tension and UV-Vis absorption data, respectively. Furthermore, the self-assembling tendency of AzoNC8 with β-cyclodextrin (β-CD) was also monitored by proton nucleic magnetic resonance (1H NMR) and scanning electron microscopy (SEM). The AzoNC8 initially formed a 1:1 inclusion complex with β-CD and subsequently 2AzoNC8 @ 2β-CD self assembly unit was formed. At 10 mM concentration, the AzoNC8/β-CD self-assembled system was found to develop a vesicular structure. The photo-responsive property of AzoNC8/β-CD was further investigated using UV-Vis, 1H NMR, and transmission electron microscopy (TEM). The self-assembled system was found to exhibit a fast photo-responsive behavior under UV light and a reversible photo-response under visible light. Interestingly, the photo-induced cis-trans isomerization altered the driving force associated with the self-assembly of AzoNC8/β-CD, thereby modulating the self-assembled morphologies. In addition, an investigation with the antitumor drug of doxorubicin hydrochloride (DOX) at different pH values revealed that the self-assembly-based vesicles exhibited a quick photo-responsive drug release and a weak acid environment could improve the rate and amount of the release. Therefore, the AzoNC8/β-CD self-assembled system might be used for the controlled release of drugs and could be a promising drug carrier.

Preparation, surface activities, and aggregation behaviors of N-acyl oligopeptide surfactants based on glycylglycine and glycylglycylglycine

With the growing concern about safety and environmental issues, amino acid-based surfactants have great potential as sustainable and eco-friendly substances. In the present study, six N-acyl oligopeptide surfactants were synthesized using fatty acid methyl esters (i.e., methyl caprate, methyl laurate, and methyl myristate) and glycyl oligopeptides (i.e., glycylglycine and glycylglycylglycine). Surface active properties and aggregation behaviors of these surfactants were investigated using surface tension, fluorescence probe, dynamic light scattering, and microscopy measurements. The adsorption at the air-water interface and aggregation in the aqueous solution depend on the structure of both hydrophilic head-groups and hydrophobic tails. Spherical vesicles were observed in the aqueous solutions of glycylglycine derivatives, whereas short tubular aggregates were found in that of corresponding glycylglycylglycine products. Intermolecular hydrogen-bonding interaction between the amide head-groups might be responsible for the different self-assembly behavior and microstructure of N-acyl oligopeptide surfactants in the aqueous solution.

Application of Molecular Simulation Technology in Improving Oil Recovery

With the continuous development of oil exploitation, the research on the oil industry has gradually shifted from macro to micro. Molecular simulation technology has attracted wide attention due to its advantages of saving costs, shortening the experimental period, and realizing the limit simulation conditions that are almost impossible under physical experimental conditions. Petroleum workers use molecular model to study the effects of different properties on adsorption and desorption. The results show that the adsorption capacity of CH4 increases with the increase of pore size and pressure, and decreases with the increase of temperature and water content. The interaction between clay minerals and CO2 was discussed, and various reactions formed after CO2 was inserted into clay minerals were discussed. Exploring the adsorption and aggregation behavior of surfactants on the interface and analyzing the influence of various properties of surfactants on oil displacement effect are helpful to optimize surfactants and improve oil displacement efficiency. Scientific research on microscopic seepage of polymer flooding has been carried out, and a large number of studies have been carried out on light hydrocarbon diffusion, polymer viscoelasticity and diffusion properties of small molecules in pores, which makes the evaluation of oil displacement effect more accurate. The application of molecular simulation technology in the above studies has obtained the properties that cannot be extracted from many macro experiments, which provides an effective method for the study of theoretical mechanism and better guides the actual production.

Influence of polymerization degree on the dynamic interfacial properties and foaming ability of ammonium polyphosphate (APP)-surfactant mixtures

Ammonium polyphosphate (APP) is an inorganic polymer and has been widely used as a flame retardant. Illustrating the interaction between APP and surfactants is significant for exploring the application of fire-fighting foam stabilized by APP/surfactant mixtures. In this work, we studied the influence of APP with different polymerization degrees on dynamic interfacial properties and foaming ability of the two oppositely charged surfactants. The results show the presence of APP only moderately affects the interfacial properties and foaming ability of the anionic surfactant, sodium dodecyl sulfate (SDS). However, when APP is added to cationic cetyltrimethylammonium bromide (CTAB) solutions, strong APP-surfactant interactions enhance the CTAB adsorption capacity at the interface leading to a decrease in the equilibrium surface tension. The results of turbidity and dynamic light scattering measurements confirm the formation of CTAB/APP complexes in the solution, which changes the adsorption kinetics and foaming ability of the solution. The difference in foaming ability and the influence of APP polymerization degree on adsorption kinetics for CTAB/APP solution can be explained by the characteristic time t* which reflects the adsorption rate of molecules from the bulk phase to the surface. Cryo-TEM results confirm that the addition of APP with different polymerization degrees strongly affects the molecular aggregation behaviour of surfactants.

Synthesis and Characterization of a Novel Short Fluorocarbon Chain Cationic Surfactant

AbstractA novel short fluorocarbon chain cationic surfactant has been synthesized to reduce the bioaccumulation of traditional fluorocarbon surfactants and maintain excellent surface properties simultaneously. The structure, surface activity, and micelle formation of surfactants have been investigated by surface tension, conductivity, dynamic light scattering, steady‐state fluorescence, Fourier transform infrared spectroscopy, and Nuclear magnetic resonance. The novel surfactant (yield more than 81%) exhibited good surface activity, the critical micelle concentration and surface tension were below 2.35 mmol L−1 and 20.54 mN m−1 in the range of temperature from 288 to 303 K, respectively. The surface tension decreased to 17.45 mN m−1 with an increase in temperature. The thermodynamic parameters (, and ) of micellization for surfactants were evaluated, which implying the micellization process was contributed primarily by the entropy driving. In addition, the aggregation behavior of surfactants was also studied in detail, which demonstrated a small micelle aggregation number of 9.40 and large size distribution of 164–342 nm.

Modulations in Self-Organization Properties of Surfactant in Aqueous Ionic Liquid Media

Abstract Ionic liquids (ILs) give a wide scope of favorable applications due to their much-upgraded properties. The strong electrostatic interactions between the cationic moiety of IL and the anionic surfactant play a very important role in the assembly of the large aggregates. We have investigated the aggregation behavior of anionic surfactants and IL in aqueous solution. Different temperatures and concentrations of IL have been taken to study the effect on critical micelles concentrations of surfactant. The critical micelle concentration values obtained by conductivity measurements are further confirmed by the fluorescence studies. The method is based on the fit of the experimental obtained raw data of fluorescence spectroscopy to a simple nonlinear category of a Boltzmann type sigmoidal function. Thermodynamical parameters of micellization Δ H m 0 $\Delta H_{m}^{0}$ , Δ G m 0 $\Delta G_{m}^{0}$ and Δ S m 0 $\Delta S_{m}^{0}$ have been considered to study the effect of aqueous IL 1-butyl-3-methylimidazolium bromide concentration and temperature on aggregation behavior of surfactant sodium dodecyl sulfate. FT-IR spectra have been studies to verify the structural changes arise in the aqueous IL and surfactant system.

Effect of Aggregation and Adsorption Behavior on the Flow Resistance of Surfactant Fluid on Smooth and Rough Surfaces: A Many-Body Dissipative Particle Dynamics Study.

To study the effect of surfactant on the resistance of wall-bound flow, the adsorption and aggregation behaviors of surfactant fluid on both smooth and groove-patterned rough surface are investigated through many-body dissipative particle dynamics (MDPD) simulation. The MDPD models of surfactants were carefully parametrized and have been validated to be able to simulate the aggregation and adsorption behavior of surfactants. The simulation results show that the surfactant in laminar flow can only increase the flow resistance on the smooth surface. On the rough surface, surfactant with strong adsorption performance on the channel wall shows a drag reduction effect at moderate concentration. The surfactant with weak adsorption properties can enhance the flow resistance, which is even more significant than that of those surfactants with no adsorption capacity. Although heating (high temperature) can generally reduce the viscosity and flow resistance of surfactant fluid, it would cause a poor drag reduction efficiency. It may arise from the destruction of the adsorption layer and the interruption of the fluid/boundary interface. Surfactant adsorption can tune the roughness of the fluid boundary on either the smooth or rough surface in a different manner, which turns out to be highly correlated to the change in flow resistance. Compared with the adsorption layer, surfactant in the bulk fluid makes a greater contribution to enhancing the flow resistance as the concentration rises. This study is expected to be helpful in guiding the application of surfactants on the micro- and nanoscale such as lab-on-a-chip nanodevices and EOR in a low-permeability porous medium.

Phase diagram and surface adsorption behavior of benzyl dimethyl hexadecyl ammonium bromide in a binary surfactant-water system

Phase diagram provides valuable information to describe the phase and aggregation behavior of surfactants. In this study, surface adsorption behavior of benzyl dimethyl hexadecyl ammonium bromide (BDHAB) surfactant in water and their phase formations have been explored. The formation of lyotropic liquid crystalline (LLC) phases in the binary surfactant–water system was analyzed by polarized light microscopy (PLM). A comprehensive phase diagram was established presenting the existence of LLC phases as a function of surfactant concentration and temperature. The observed PLM images reveal that the BDHAB–H2O system exhibits isotropic (L1), hexagonal liquid crystalline (H1), cubic (V1), and lamellar (L∞) phases in a sequential pattern with the increase of surfactant concentration. The recorded LLC phases for bi-tail BDHAB–H2O system have also been compared with the phase diagram of single tail cetyl trimethyl ammonium bromide (CTAB)–H2O system. The present study evidence that the surfactant morphology (i.e., alkyl chain length and surfactant head-group area) has a significant influence on the formation of micellar aggregates. In addition, surface tension measurements were also performed to observe the surface adsorption behavior of BDHAB surfactant. This study will be beneficial in understanding the micelle formation and solubilization behavior of bi-tailed quaternary ammonium cationic surfactants to optimize its colloidal formulations.

Aggregation behavior of surfactants with cationic and anionic dendronic head groups

HypothesisIonic dendronic head groups possess very different structural features than simple surfactant head groups. Accordingly, their self-assembly behavior is expected to differ from that of conventional surfactants. The number of generations of the headgroup should play a particularly relevant role. ExperimentsA novel type of surfactants with different dendronic head groups (cationic and anionic) was studied in this work. A systematic variation of the number of generations of the head group (n = 1, 2, and 3), of the head group charge (cationic and anionic), and of the length of the hydrophobic chain (hexanoyl and hexadecanoyl chains) was performed and the self-assembly behavior probed by means of small-angle neutron scattering (SANS) in order to obtain detailed structural insights. FindingsThe analysis of the scattering data shows that the general packing parameter concept applies also to dendrimeric surfactants and a larger head group results in smaller aggregates. However, in contrast to conventional surfactants, increasing the head group size results in a stronger tendency to self-aggregate, as a consequence of the head group’s partly hydrophobic character. Another peculiarity of the self-assembled aggregates, is the low aggregation numbers and the high water content within the micelle, as a result of the highly branched head group.

Surface activity, foam properties and aggregation behavior of mixtures of short-chain fluorocarbon and hydrocarbon surfactants

Surface activity, foam properties and aggregation behavior of a short-chain fluorocarbon surfactant (FS-50), an anionic hydrocarbon surfactant (sodium dodecyl sulfate, denoted as SDS) and FS-50/SDS mixture are systemically studied for the first time in this paper. Surface activity was characterized by surface tension. Foam properties, including foamability and foam stability, of the mixed systems were studied based on the standard Ross-Miles method. The aggregation behavior of the surfactant solution was observed by using cryo-transmission electron microscopy (Cryo-TEM). The results show that FS-50 exhibits good surface activity and foam properties, which reveals that as a kind of environment friendly short-chain fluorocarbon surfactant, FS-50 is a perfect substitute of long-chain ones. Surface activity and foam properties of FS-50/SDS mixed system are enhanced by adding FS-50 and further improved by the increase of FS-50 concentration. The foam properties are enhanced by tightening the arrangement of surface adsorbed molecules at the liquid-air interface. A synergistic interaction exists in the mixture of short-chain FS-50 and SDS, which is produced through microscopic spheroidal-to-wormlike transition. Finally, the macroscopic performance of FS-50/SDS mixed solution is enhanced by the changes of composition and morphology of the adsorbed film layer. This work shows an environmental friendly surfactants mixed system and provides a more comprehensive perceive of the relationship between macroscopic properties and micro-aggregation structure of short-chain fluorocarbon and hydrocarbon surfactants mixed system.

Synthesis, Properties, and Aggregation Behavior of Tetrasiloxane-Based Anionic Surfactants.

Three silicone surfactants, 3-tris(trimethylsiloxy)silylpropyl sulfonate with different alkaline counterions (lithium, sodium, and potassium), were synthesized for the first time. Their chemical structures were confirmed by FT-IR spectra, 1H NMR, and ESI-MS, and their behaviors in aqueous solutions were investigated by surface tensiometry, electrical conductivity, dynamic light scattering, and different transmission electron microscopy techniques. These anionic silicone surfactants exhibited remarkable surface activity and could reduce the surface tension of water to as low as 19.8 mN/m at the critical aggregate concentration (CAC). The adsorption and aggregation behaviors of these surfactants were assessed by determining the adsorption efficiency, minimum average area per surfactant molecule, and thermodynamic parameters. The cryo-TEM results verified that these molecules could form vesicles in water above the CAC. Moreover, the lowest surface tension, the smallest CAC value, and the largest aggregate size have been reached with potassium counterions. Thus, the different behavior of these surfactants in water can be explained by the different sizes of the hydrated ions.

Numerical simulations on effects of ionic / nonionic surfactant on oil‐water interface using dissipative particle dynamics

AbstractEffects of surfactants on oil/water interface are studied using dissipative particle dynamics (DPD) at the mesoscopic scale. With a surfactant model, the effects of concentration of three types of surfactants, including ionic surfactant, nonionic surfactant, and the compound system of ionic and nonionic surfactant, on interfacial tension are analyzed in this study. Also, the distributions of interfacial tension and mean interfacial density are predicted. Simulated results indicate that the interfacial tension decreases with an increase of surfactant concentration. As the surfactant concentration increases to a certain value, the surfactant at the oil‐water interface is saturated, and the interfacial tension will in‐depend on surfactant concentration. It turns out to be that surfactants can be saturated just at the oil‐water interface once its concentration reaches a certain value. A proper mixed ratio of compound system can reach a prime effect. Moreover, the inorganic salts can improve the interfacial efficiency of both ionic and nonionic surfactants, and lower interfacial tension. In addition, the temperature influences on surfactant aggregation behavior at the oil‐water interface is discussed. Copyright © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.