Effect Of Surfactant Structure Research Articles

Size and shape matter for micellar catalysis using light-responsive azobenzene surfactants.

The micellar catalysis of a model Claisen-Schmidt aldol condensation reaction using heterogeneous nanoreactors based on cationic azobenzene trimethylammonium bromide (AzoTAB) photosurfactants is investigated. Under UV irradiation, AzoTABs undergo a trans-cis photoisomerisation, which changes not only the critical micelle concentration, but also the shape and size of the micelle. The effect of surfactant structure (tail and spacer lengths), concentration and temperature on the reaction yield were investigated. Monitoring of the zeta potential during the reaction indicated that it proceeds at the micelle/water interface for AzoTABs, with the enolate intermediate stabilised in micelle/water interface (i.e. the Stern layer). The reaction yield was found to correlate directly to micellar shape and size, with smaller, more spherical micelles typical of cis-AzoTABs favouring higher reaction efficiencies.

Emulsion formation and stability of surfactant–polymer flooding

Emulsification plays a pivotal role in the process of enhanced oil recovery, especially in chemical flooding. Surfactant–polymer flooding is a promising technique with significant potential for improving oil recovery in medium and high permeability oilfields in China. Emulsification has emerged as one of the key mechanisms facilitating oil recovery in surfactant–polymer flooding. This study aimed to assess the effects of surfactant structure and concentration, polymer, oil–water ratio, clay content, and injection rate on the formation of different emulsion types and their stabilities. The assessment was conducted based on the actual conditions of surfactant–polymer flooding in the Qizhong area of the Xinjiang oilfield. The findings revealed that KPS-1 (petroleum sulfonate) demonstrated superior emulsifying and solubilizing abilities for crude oil compared to BS-18 (betaine), whereas BS-18 exhibited better emulsifying stability. KPS, which was a combination system of KPS-1 and BS-18, displayed favorable emulsifying ability. However, the emulsifying stability of the three surfactants decreased in the presence of HPAM (hydrolyzed polyacrylamide). The oil–water ratio primarily influenced the morphology of the emulsion. When the oil–water ratio exceeded 6:4, a water-in-oil emulsion was formed, and the viscosity of the emulsion reached its maximum at an oil–water ratio of 7:3. Moreover, clay demonstrated a significantly high ability to emulsify, resulting in the formation of emulsions with increased viscosity and robust stability. Regarding the injection rate, effective emulsification occurred when the injection rate reached 1 m/d, while emulsions with high viscosity were observed at an injection rate of 7 m/d.

The structure effect on the physicochemical properties of Gemini surfactants used as viscosity reducer for heavy oil

The structure of surfactants is a key factor affecting their physicochemical properties. Our earlier work synthesized Gemini surfactants CEA-n with different structures. In this paper, the effects of polyether chain length, spacer groups number and the hydrophobic alkyl chain length of surfactants CEA-n on the interfacial properties, wettability, rheological properties and emulsion stability were fully studied in detail, and the effects of surfactant structure on their temperature tolerance and salt resistance properties were explored. The results showed that the variation of polyether chain length of surfactant molecules had the greatest impact on the interfacial tension (IFT), and the surfactants with longer alkyl chains had better interfacial film strength. The wettability of various surfactant systems was investigated by the sessile drop method, and the contact angle decreased remarkably from 92.6° to 17.9° in a short time (300 s) after adding surfactant CEA-6. Judging from the fluid type, each heavy oil emulsion system exhibited pseudoplastic fluid characteristics, and dilute shear phenomenon was observed in the range of 0–50 s−1 with an increasing shear ratio. The particle size, dispersibility and coalescence of the heavy oil O/W emulsion droplets of each system were observed through the microscopic images of the emulsions, and the factors affecting the stability of the emulsions were systematically studied by bottle test. It was found that the increase of oil-water ratio, surfactant concentration and mixing speed would improve the stability of O/W emulsions, while high temperature would accelerate the demulsification process. All these results established the structure-property relationship of surfactant molecules.

Effect of surfactant hydrophobic chain equivalence on the oil-water interface and emulsion stability: A dissipative particle dynamics and experimental study

Gemini surfactants have shown great potential and have become a popular topic of research and are considered a novel alternative to conventional surfactants because of their extraordinary physical and chemical properties. In this study, a series of surfactants with similar structures but different numbers of hydrophobic chains were constructed, and their effects on an oil–water interface were systematically investigated using dissipative particle dynamics (DPD) simulations. The effects of these surfactants on the behavior of the oil–water interface were further analyzed when the surfactant concentrations in the system were the same and when the numbers of hydrophobic chains in the system were the same. The effects of surfactant structure on the stability of the emulsion were further investigated on the basis of an analysis of the effects of the surfactants on the behavior of the oil–water interface. The results showed that Gemini and tri-cationic surfactants transitioned the oil–water interface from a lamellar structure to an emulsion form at lower concentrations compared to conventional single-chain surfactants, (e.g., 39.0% for SC-21, 33.0% for DC-21, and 15.0% for TC-21), but this superiority may be due to the absolute advantage of concentration rather than structural properties. The use of Gemini and tri-cationic surfactants have a positive effect on emulsion stabilization when the surfactant concentrations are the same. However, the use of Gemini and tri-cationic surfactants, which have more complex synthetic routes, is not necessary. The present work provides a theoretical basis for the rational selection of surfactants for emulsion applications.

Molecular dynamics simulations of the structure–property relationships of DDA/anionic surfactant mixtures at the air/water interface

In this study, three anionic surfactants (sodium oleate (NaOl), sodium dodecyl sulfonate (SDS) and naphthenic acid (NA)) were combined with dodecylamine (DDA) with molar ratios of 1:1 to investigate the interfacial behaviors of DDA/anionic surfactant mixtures at the air/water interface. The self-assembly processes and dynamic properties of the monolayers were then clarified by using molecular dynamics simulations to explore the effects of surfactant structure on surface activity. Compared with the pure DDA system, the mixtures that were oriented more perpendicularly at the air/water interface and had thicker hydrophilic films exhibited reduced surface tensions and improved hydrophobicity. The interactions between polar groups of the anionic surfactants and DDA reduced the electrostatic repulsions between DDA cations and increased the adsorption capacities of the mixtures at the air/water interface. The molecular dynamics simulations showed that different DDA/anionic surfactant mixtures had different surface activities. Due to the strong electronegativity of the sulfonic group, the interactions between SDS and DDA were the strongest, the amine groups showed a higher hydration degree, and the compatibility of the surfactant tails was better than those of the other anionic surfactants with DDA, which exhibited stronger synergistic effects. The simulation results were consistent with our previously reported data on flotation and surface tension, which may provide guidance for selection of collectors and foaming agents used in the flotation process.

Luminescent probe synthesis for oxygen visualization technique: Application to the effect of surfactant structure on oxygen mass transfer

Planar Laser Induced Fluorescence with Inhibition (PLIF-I) is a powerful technique for studying the local gas/liquid oxygen mass transfer from a single rising bubble. However, to track oxygen in the liquid phase, it is necessary to use an oxygen sensitive luminescent probe, which needs to be unreactive toward the liquid phase. This article presents the synthesis of a fluorophore, [Ru(dpp-diSO3)3]Na4, to be used in liquid phases containing anionic molecules. To avoid electrostatic interactions, the fluorophore and the component present in the liquid phase need to have the same charge. Thanks to the use of this new luminescent probe in PLIF-I application, the influence of the chain length of anionic surfactants (dodecyl sulfate sodium salt and tetradecyl sulfate sodium salt) on oxygen mass transfer has been studied at different concentrations (1.3 × 10-3-2.5 × 10-7 mol.L-1). Results show that, for a given bulk concentration, the longer the hydrophobic chain, the greater the decrease in velocity and mass transfer coefficient. These results are compared with those of a previous paper dealing with length of cationic and nonionic surfactants and a correlation is proposed, taking account of the intrinsic properties of surfactants and their concentration in the liquid phase.

The potential and mechanism of nonionic polyether surfactants dissolved in CO2 to improve the miscibility of CO2–hydrocarbon systems

Certain unique reservoir conditions and technical difficulties have greatly limited the use of CO2 miscible injection in unconventional reservoirs. Lowering the miscibility pressure to realize the miscibility of CO2 and crude oil is critical for achieving the most efficient recovery process. In this study, we investigated whether nonionic polyether surfactants could improve the miscibility of CO2 and hydrocarbons. And an improved experimental method for a quantitative evaluation of additive efficiencies in lowering the miscibility pressure was introduced for the first time. The dissolution behaviors of nonionic polyether surfactants in CO2 and phase behaviors of CO2–hydrocarbon systems with and without surfactant additives were conducted. The effects of surfactant structure and concentration and temperature on the solubility of nonionic polyether surfactants in CO2 along with the efficiency of miscibility pressure reduction for CO2–hydrocarbon systems were analyzed. The results showed that the polyoxypropylene alkyl ethers exhibited excellent potential for improving the miscibility of the CO2 and hydrocarbons, especially when low molecular weight surfactant molecules with high polyoxypropylene group content were used. The first-contact miscibility pressure (FCMP) of the mixed oil and CO2 could be reduced by as much as 22.51% with 3 wt% C4(PO)3 addition. Furthermore, a mechanistic understanding showed that the solubilization of the CO2 caused by polyether reverse micelles resulted in a reduction of miscibility pressures for CO2–hydrocarbon systems. The study results and the novel evaluation method provided guidance for designing and selecting appropriate additive structures to reduce miscibility pressures of CO2–oil systems and meet the CO2 miscible injection technology requirements.

CONDUCTOMETRIC STUDY OF LIGAND STRUCTURE INFLUENCE ON THE Pb(II) COMPLEXATION WITH CROWN ETHERS

The conductometric study of ligand structure influence on the Pb(II) complexation with crown ethers in different solvents has been investigated. In this paper, the complexation reaction of macrocyclic ligand, 18-crown-6 (18C6), dibenzo-18-crown-6 (DB18C6), and Pb(II) cation was studied in different solvents: dichloromethane (DCM) and 1,2- dichloroethane (1,2-DCE). The effects of surfactant structure (Triton X-100 and Triton X-45) on the conductivity of the Pb(II) complex with 18-crown-6 and dibenzo-18-crown-6 ether have been investigated. The conductance data showed that the stoichiometry of the complexes in most cases is 1:1(ML). It is also demonstrated that the influence of crown ethers is deeply affected by the organic solvent used. In the solvents studied, the stability of the resulting complexes showed higher stability in dichloromethane comparing with 1,2- dichloroethane. Macrocyclic ligand 18-crown-6 showed more suitable for complexation of Pb(II) ions compared to dibenzo-18-crown-6. Adding a surfactant affected the higher absolute values of the conductivity of systems, but not the change in the stoichiometric ratio between a metal ion and macrocyclic ligand.

Decrease in hydrophilicity and moisture readsorption of lignite: Effects of surfactant structure

The low moisture content of lignite is essential to its high utilization efficiency. There has been increasing attention given to the adsorption of surfactants to decrease the hydrophilicity and moisture readsorption of lignite. This has focused on findings surfactants that are effective, convenient, and inexpensive. To understand the effect of surfactant structure on decreased lignite hydrophilicity, eighteen surfactants including conventional types of surfactants were used for lignite treatment. Wetting heat results indicated that cationic and non-ionic surfactants were superior in their performance to decrease the hydrophilicity of lignite compared to anionic surfactants with the same hydrophobic alkyl chain. Ethanediyl-1,2-bis(dimethyl dodecyl ammonium bromide) (12-2-12) and lauryl polyoxyethylene ether (C12EO9) were found to be the most effective cationic and non-ionic surfactants in these samples, respectively. Linear shapes, long alkyl chains, and gemini structures were beneficial to decreasing the hydrophilicity of lignite. Structures to be avoided included anionic types, branches, aromatic rings, and glucoside. The adsorbed surfactant layer covered the oxygen containing functional groups on the surface of the lignite, and also blocked lignite pores to reduce the storage space of water, effectively reducing the hydrophilicity of the lignite. The contribution of the coverage of oxygen-containing functional groups was found to be more significant. In addition, we demonstrated the consistency between moisture readsorption and wetting heat in terms of presenting hydrophilicity of lignite and their differences were also discussed. Our results provide a reference for selecting an appropriate strategy and further developing the application of surfactants to decrease lignite hydrophilicity.

Interfacial ordering of tristearin induced by glycerol monooleate and PGPR: A coarse-grained molecular dynamics study.

We use coarse-grained molecular dynamics simulations to study the effect of surfactant structure on the ordering of bulk tristearin at an oil-water interface. In the absence of surfactant, tristearin acyl chains are marginally aligned normal to the interface. The surfactant glycerol monooleate (GMO), a common small-molecule monoacylglycerol (MW: 357 g/mol), preferentially adsorbs to the oil-water interface, displacing more of the tristearin as its concentration increases. The tristearin that remains at the interface is closely aligned normal to the interface. Adjacent to the interface, bulk tristearin increasingly aligns with its acyl chains entwined with the GMO acyl chain, which also preferentially aligns normal to the interface. In contrast, polyglycerol polyricinoleate (PGPR), a bulkier, polymeric surfactant (MW: 1398 g/mol for a molecule with five monomers), both displaces tristearin from the interface and reduces the alignment of the molecules that remain. We suggest that the similar fatty acid moieties of GMO (oleic acid) and tristearin (stearic acid) lead to liquid-state association and alignment, the latter of which can then serve as a template onto which tristearin crystals can nucleate. Conversely, by both displacing tristearin from the interface and reducing alignment below that of the surfactant-free system, PGPR eliminates the possibility of tristearin interfacial crystallisation.

Effect of triblock copolymer surfactant composition on flow-induced phase inversion emulsification in a tapered channel

HypothesisPhase inversion emulsification (PIE) is a process that inverts the dispersed and continuous phases of an emulsion and is useful for preparing emulsions that are challenging to produce using conventional techniques. A recent work has shown that PIE can be induced by flowing an emulsion through a tapered channel. Although prior studies have shown that flow-induced PIE (FIPIE) is influenced by the flow conditions and wetting properties of the channel surface, little is known about the effect of surfactant structure on FIPIE. We hypothesize that FIPIE is affected by the composition and structure of the surfactant used for emulsion stabilization. ExperimentsWe use Pluronics, a series of ABA triblock copolymers composed of hydrophilic poly(ethylene oxide) (PEO) and hydrophobic poly(propylene oxide) (PPO) with various lengths (A = PEO, B = PPO), as model surfactants to test this hypothesis. We observe that triblock copolymer surfactants with long PEO blocks suppress FIPIE. A scaling analysis based on a polymer brush model qualitatively agrees with the experimental observation. We also show that for small molecular weight Pluronics, FIPIE is significantly suppressed when Pluronics with large PPO blocks are used. FindingsOur results strongly indicate that the steric repulsion provided by the PEO blocks as well as the dilatational elasticity provided by the PPO blocks are key factors that control the FIPIE process.

Effect of surfactant structure on charge storage properties in Co3O4–based electrodes

Co3O4 powders are synthesized by a controllable microwave process in the presence of nonionic surfactants characterized by various structures. The influence of the surfactant structure on the charge storage performance of Co3O4 –based electrode is commented through the specific surface area and morphology of Co3O4 powder. In the absence of surfactants, Co3O4 layers are self-organized into microspheres. When linear PEG 2000 or Triton X100 polymers are used as surfactants, Co3O4 microspheres unfold into particles. However, a nanorods-like morphology is obtained with the multi-branched Tween 20 surfactant. Such a unique architecture exhibits remarkable electrochemical performance with high capacity and suitable cycle life after 2000 cycles in 3 M KOH aqueous solution. Increasing the specific surface area results in the improvement of the electrochemical performance. The specific capacity values deduced from cyclic voltammetry experiments are found to increase in the following order: Co3O4 -without surfactant (60 mAh g−1) < Co3O4-Triton X100 < Co3O4-PEG 2000 < Co3O4-Tween 20 (126 mAh g−1). The exceptional charge storage performance of Co3O4 elaborated with Tween 20 is also confirmed galvanostatically in term of high capacity retention. It shows that 70% of the capacity is maintained upon a gradual increase of the applied current density from 5 to 15 A g−1.

Interfacial behaviors of betaine and binary betaine/carboxylic acid mixtures in molecular dynamics simulation

The interfacial properties of betaine surfactants and betaine/carboxylic acid mixtures at decane-water interface have been studied via molecular dynamics simulations. The effect of surfactant structure on the surfactant orientation is discussed firstly based on the pure betaine systems. Then Synergistic effect of mixed Betaine/carboxylic acid systems at the interface is explored using mass density profile, interfacial thickness and spatial distribution function. Based on the simulated results, one can find the hydrophilic tail of betaine has a strong tendency to flat on the interface, long alkyl main chain tends to stretch into oil body and dominates the orientation of hydrophobic chain while benzene ring can change and fix the order of alkyl chain to some extent. Carboxylic acid molecules locate in the crack of ASB18 hydrophobic chains and the addition of appropriate carboxylic acid molecules could induce an impressive decrease of interfacial tension. Our simulated results prove experimental conjecture and reveal the mechanism about the decrease of interfacial tension at molecule level, which is important for the enhanced oil recovery processes.

Characterizing the impact of surfactant structure on interfacial tension: a molecular dynamics study.

The effect of sodium branched-alkylbenzene sulfonates on the NaCl solution/oil interface was studied via classical molecular dynamics simulation. The interfacial properties were found to depend on the surfactant concentration and to change dramatically when the concentration exceeded a critical value, the simulated limit area (A c). When A c is not close to the theoretical saturated adsorption area (A min), the surfactant cannot produce ultralow interfacial tension (IFT). When A c is equal or almost equal to A min, the effect of the structure of the surfactant must be considered to determine if ultralow IFT is possible: if the sizes of the hydrophobic and hydrophilic groups in the surfactant are similar, the surfactant can produce ultralow interfacial tension (and vice versa). Based on the results of these studies, the effect of surfactant structure on the interfacial properties of the system was investigated, and a method of gauging the IFTs produced by different surfactants was proposed that should prove very useful when designing the optimal surfactant structure to achieve ultralow IFT. Graphical Abstract The interfacial properties of water/surfactant/oil system, such as interfacial thickness and IFT, depending on the surfactant concentration and changing dramatically when the concentration exceed a critical value.

Development of siloxane-based amphiphiles as cell stabilizers for porous shape memory polymer systems

HypothesisPolyurethane foaming surfactants are cell stabilized at the polymer-gas interface during foam blowing to prevent bubble coalescence. Siloxane-based surfactants are typically used to generate a surface tension gradient at the interface. The chemical structure of the hydrophobic and hydrophilic units affects surfactant properties, which can further influence foam morphology. ExperimentsSiloxane-polyethylene glycol (PEG) ether amphiphiles were synthesized in high yield via hydrosilylation to serve as surfactants for shape memory polymer (SMP) foams. Hydrophobic units consisted of trisiloxane and polydimethyl siloxane, and PEG allyl methyl ether (n=8 or 25) was the hydrophilic component. Upon confirming successful synthesis of the surfactants, their surface tension was measured to study their suitability for use in foaming. SMP foams were synthesized using the four surfactants, and the effects of surfactant structure and concentration on foam morphology were evaluated. FindingsSpectroscopic data confirmed successful siloxane-PEG coupling. All surfactants had a low surface tension of 20–21mN/m, indicating their ability to reduce interfacial tension. SMP foams were successfully fabricated with tunable cell size and morphology as a function of surfactant type and concentration.

Interfacial activity of alkyl hydroxyl sulfobetaine against crude oil

ABSTRACTTo study the interfacial activities of zwitterionic surfactant against crude oil, four alkyl hydroxyl sulfobetaines were synthesized. The effects of surfactant structure, concentration, salinity of formation water, and crude oil composition on interfacial activities were discussed. It shows that the octadecyl hydroxyl sulfobetaine can achieve ultralow interfacial tension at the concentrations no less than 0.001%, exhibiting a good interfacial activity and a very strong antidilution ability. The salinity of formation water has no obvious effect on lowering the interfacial tension and the polar component in crude oil is very crucial for the production of ultralow interfacial tension. This work is important for enhanced oil recovery.

Mixed micellization of dimeric surfactant–amphiphilic drug systems: effect of surfactant structure

For their applications as drug delivery vehicles, the mixed interfacial/micellar behaviour of zwitterionic, cocogem and anionic dimeric surfactants with an amphiphilic drug imipramine hydrochloride in aqueous solutions has been investigated.

Reverse micellar extraction of bromelain from pineapple peel – Effect of surfactant structure

Pineapple peel is generally disposed or used as compost. This study was focused on extracting bromelain from pineapple peel by using reverse micelles. It was found that gemini surfactant C12-8-C12·2Br (octamethylene-α,ω-bis(dimethyldodecylammonium bromide)) showed distinctive advantage over its monomeric counterpart DTAB (dodecyl trimethyl ammonium bromide); under optimized condition, the bromelain extracted with C12-8-C12·2Br reverse micelle had an activity recovery of 163% and a purification fold of 3.3, while when using DTAB reverse micelle, the activity recovery was 95% and the purification fold was 1.7. Therefore, the spacer of gemini surfactant should play a positive role in bromelain extraction and may suggest the potential of gemini surfactant in protein separation since it has been so far rarely used in relative experiments or technologies.

Varying photoluminescence emission of CdS nanoparticles in aqueous medium: A comparative study on effect of surfactant structure

The photoluminescent (PL) properties of colloidal semiconductor nanoparticles (NPs) can be strongly affected by coupling of the organic moieties on their surfaces. A deeper understanding of various factors governing the actual PL emission of Cadmium sulfide (CdS) NPs is important to utilize the same in functional devices. In present work, a comparative investigation on surfactant-structure dependent PL emission of CdS NPs prepared by a convenient chemical precipitation method has been described. By varying the surfactant (stabilizer) species on NP’s surface, the PL emission of CdS NPs varies significantly under similar conditions. Additionally, the effect of photoactivation using normal daylight and UV-light has also been studied on PL of CdS NPs. Photo-dissolution of CdS NPs under both normal as well as UV-light has produced smaller NPs. The PL emission performance of the NPs has also been improved manifold after photoactivation which has been explained in the terms of changing surface states.

Effect of surfactant structure on the mixed micelle formation of cationic gemini–zwitterionic phospholipid systems

The micellization behavior of mixed zwitterionic/cationic solutions, that is, of zwitterionic phospholipid, 1, 2-dioctanoyl-sn-glycero-3-[phospho-L-serine] (sodium salt) (PL) and cationic gemini surfactants, alkanediyl-α,ω-bis(dimethylalkylammonium bromide (alkyl: 14 or 16 and alkane: butane, pentane or hexane) (m-s-m), have been studied by surface tension measurements. Various physicochemical properties, viz., critical micelle concentration (cmc), surface excess concentration (Γmax), minimum area per molecule (Amin), interaction parameters (βm, βσ), and thermodynamic parameters such as standard Gibbs energy of micellization (ΔGmic°), standard Gibbs energy of adsorption (ΔGads°), and excess free energy of mixing (ΔGexm,ΔGex°), have been evaluated. The obtained results indicate that the mole fraction of PL in the mixed micelles, calculated on the basis of Rubingh's model, is different from stoichiometric mole fraction of PL (α1). The negative values of ΔGmic° and ΔGads° show that the micelle formation and adsorption of surfactants at the air/solution interface is energetically favorable with the magnitude of ΔGads° greater than that of ΔGmic°. The negative values of ΔGexm and ΔGexσ indicate better stability of the mixed systems. The insights presented herein on the gemini-phospholipid mixed micelle properties may find use towards their applications in the relevant areas of solubilization/drug delivery/etc.