Effects of nonionic surfactant on the rheological property of associative polymers in complex formulations

The rheological properties of hydrophobically modified ethoxylated urethane (HEUR) were investigated in the presence of a nonionic surfactant, polyoxyethylene stearyl ether (C₁₈(EO)₂₀). The presence of nonionic surfactants played an important role in tuning the rheological properties of HEUR aqueous solutions. Observing both plateau modulus and viscoelastic relaxation time of HEUR aqueous solutions with varying the concentration of C₁₈(EO)₂₀ allowed us to demonstrate that C₁₈(EO)₂₀ readily interacts with the hydrophobic segments of HEUR polymers, which eventually formed a strong micellar network. Moreover, the micellar network formed at a critical concentration of C₁₈(EO)₂₀, ∼0.6% w/v, was indeed stable against both ionic strength and pH in the aqueous medium and complex formulations, such as a colloid suspension and an oil-in-water emulsion, thus providing more practical applications as thickeners for a wide variety of complex formulations.     

Effect of mixing protocol on formation of fine emulsions

Emulsions are usually stabilised with a mixture of surfactants with different hydrophilicity. The initial partitioning of surfactants between the dispersed phase and continuous phase, and how these phases are brought into contact, can significantly affect the emulsification processes. Dynamic-phase behaviour maps were prepared to allow for a systematic investigation of the effects of emulsification routes on emulsion properties. Six semibatch modes of additions with constant surfactant concentration across the routes were selected. For a target cyclohexane-in-water emulsion using a pair of polyoxyethylene nonylphenyl ether surfactants with a specified HLB and water volume fraction, fine droplets could form only if water dissolving the water-soluble surfactant was added to the oil dissolving the oil-soluble surfactant. This route allowed the transitional inversion to occur and as a result fine droplets were formed due to an ultra-low interfacial tension. The addition of water dissolving the water-soluble surfactant to oil dissolving the oil-soluble surfactant, direct emulsification method, produced by far large droplets because of a rather high interfacial tension. In a series of experiment, the semibatch direct and phase-inversion emulsification method, were assimilated in situ. The impeller location was used as a variable that controls which phase is added as the dispersed phase. The location of impeller in relation to the interface did not affect the emulsion drop size at a high agitation rate, but it did at a low agitation rate. Under low agitation speed and when the impeller was placed in the oil phase, the oil layer progressively, but slowly, dragged the water phase and eventually inverted to an oil-in-water emulsion, indicating that transitional-phase inversion has locally occurred in the oil layer. At a high agitation speed the mechanical energy provided by the impeller homogenised the emulsion instantaneously and did not allow the optimum formulation and the associated ultra-low interfacial tension to be reached regardless of location of the impeller. A high impeller speed increased drop size by transforming the transition inversion mechanism to a catastrophic mechanism under which the size of drops is mainly determined by the mechanical energy provided. This paper aims to show how some of the complexities involved in emulsification processes can be explained by consulting with dynamic-phase maps.     

表面活性剂和四烷基溴化铵的复配 Ⅱ.四乙基溴化铵对离子型表面活性剂在气/液表面吸附行为的影响

用表面张力法研究了有机电解质四乙基溴化铵（（Ｅｔ）４ＮＢｒ）对离子型表面活性剂十二烷基硫酸钠（ＳＤＳ）和十二烷基三甲基溴化铵（ＤＴＡＢ）在气／液表面吸附行为的影响。表明（Ｅｔ）４ＮＢｒ提高了ＳＤＳ和ＤＴＡＢ降低水溶液表面张力的效率。但（Ｅｔ）４ＮＢｒ仅提高ＤＴＡＢ降低水溶液表面张力的能力,却反而削弱了ＳＤＳ降低水溶液表面张力的能力。通常电解质对离子表面活性剂表面吸附层的影响主要来自与表面活性离子电性相反的反离子,它们屏蔽了表面活性剂离子头基间的电荷,致使表面活性剂在气／液表面层排列紧密。有机电解质离子（Ｅｔ）４Ｎ＋作为反离子时,除了具有电解质离子的通常性能外,其乙基和表面活性剂碳氢链间还有一定程度的弱疏水相互作用,使部分（Ｅｔ）４Ｎ＋离子嵌入ＳＤＳ吸附层的离子头基区中,较大（Ｅｔ）４Ｎ＋离子的嵌入使周围的ＳＤＳ碳氢链排列疏松,改变了朝向空气面的表面碳氢链覆盖层结构,从而削弱了其降低表面张力的能力。     

Molecular dynamics simulation study on π-π stacking of Gemini surfactants in oil/water systems

Whereas the π-π stacking interactions at oil/water interfaces can affect interfacial structures hence the interfacial properties,the underlying microscopic mechanism remains largely unknown.We reported an all-atom molecular dynamics(MD) simulation study to demonstrate how the Gemini surfactants with pyrenyl groups affect the interracial properties,structural conformations,and the motion of molecules in the water/n-octane/surfactant ternary systems.It is found that the pyrenyl groups tend to be v...     

Wettability of Polymeric Solids by Aqueous Solutions of Anionic and Nonionic Surfactant Mixtures

Measurements of the surface tension (γ _LV) and advancing contact angle () on poly(tetrafluoroethylene) (PTFE) and poly(methyl methacrylate) (PMMA) were carried out for aqueous solutions of sodium decyl sulfate (SDS) and p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycol) (TX100) and their mixtures. The results obtained indicate that the values of the surface tension and contact angles of solutions of surfactants on PTFE and PMMA surfaces depend on the concentration and composition of the surfactant mixtures. Calculations based on the Lucassen-Reynders equation indicate that for single surfactants and their mixtures at a given concentration in the bulk phase the values of surface excess concentration of surfactants at water–air and PTFE–water interfaces are nearly the same, so the adsorption of the surfactants at water–air and PTFE–water interfaces should also be the same. However, the adsorption of TX100 and its mixtures with SDS at water–air interface is higher than that at PMMA–water interface, which is confirmed by the ratio of absolute values of molecular interaction parameters at these interfaces calculated on the basis of Rosen approach. If we take into account the hydration of the poly(ethylene oxide) chains of TX100 and acid and base parameters of the surface tension of water it appears that the PMMA surface is covered by the 'pure' water molecules from the solution or molecules connected with the chain of nonionic surfactant. On the other hand, the lack of SDS molecules at the PMMA–water interface may result from the formations of its micelles which are connected with the TX100 chain.     

Surface activity of mixtures of narrow-range distributed alcohol oxyethylates and sodium dodecylbenzenesulfonate

Surface and interfacial tension, emulsion inversion temperature, and detergency were determined for mixtures of sodium dodecylbenzenesulfonate and narrow-range distributed alcohol C₁₂−C₁₄ oxyethylates of different hydrophilicity. The mixtures of ionic and nonionic surfactants behave similarly to nonionic and ionic surfactants at the air/water and hydrocarbon/water interfaces, respectively. The air/water interface is mainly occupied by nonionic surfactant molecules. However, the interfacial tensions for mixtures of nonionic and ionic surfactants are similar to those of sodium dodecylbenzenesulfonate. Mixtures of narrow-range distributed oxyethylates and sodium dodecylbenzenesulfonate have a higher detergency at 40°C than individual components.     

Synthesis,Micellization, and Surface Activity of Novel Linear-Dendritic Carboxylate Surfactants

Two generations of novel linear-dendritic carboxylate surfactants C₁₈-G₁-(COONa)₂ and C₁₈-G₂-(COONa)₄ have been synthesized by the divergent method and their structures are characterized by ¹H Nuclear Magnetic Resonance and Infrared analysis. The electrical conductivity measurement is used to measure the Krafft temperatures of C₁₈-G₁-(COONa)₂ and C₁₈-G₂-(COONa)₄, which are much smaller than those of the corresponding conventional surfactant sodium stearate. The markedly enhanced solubility of two linear-dendritic surfactants is ascribed to the high hydrophilicity of surfactant headgroups induced by the carboxylate and ester groups. The critical micelle concentration (CMC) values obtained from both the electrical conductivity and surface tension measurements indicate that the micellizations of linear-dendritic surfactants become favorable with the increase in the number of the surfactant headgroup. However, the surface activity parameters including the surface tension at the CMC, maximum surface excess, and minimum surface area reveal that C₁₈-G₁-(COONa)₂ exhibits greater efficiency in absorbing at the air/water interface compared to C₁₈-G₂-(COONa)₄, owing to their different steric repulsions of the surfactant headgroups. In addition, C₁₈-G₁-(COONa)₂ and C₁₈-G₂-(COONa)₄ have higher emulsifying ability than the conventional surfactants sodium stearate and sodium octadecyl sulfate.     

Surfactant (in situ)–Surfactant (Synthetic) Interaction in Na2CO3/Surfactant/Acidic Oil Systems for Enhanced Oil Recovery: Its Contribution to Dynamic Interfacial Tension Behavior

The effect of synthetic surfactant molecular structure on the dynamic interfacial tension (DIFT) behavior in Na₂CO₃/surfactant/crude oil was investigated. Three surfactants, a nonionic (iC₁₇(EO)₁₃), an alcohol propoxy sulfate (C_14–15(PO)₈SO₄), and sodium dodecyl sulfate (SDS) were considered in this study. Sodium tripolyphosphate (STPP) was added to ensure complete compatibility between brine and Na₂CO₃. In Na₂CO₃/iC₁₇(EO)₁₃/oil and Na₂CO₃/C_14–15(PO)₈SO₄/oil systems, a strong synergistic effect for lowering the dynamic interfacial tension was observed, in which the dynamic IFT are initially reduced to ultralow transient minima in the range 1.1 × 10^?3–6.6 × 10^?3 mNm^?1 followed by an increment to a practically similar equilibrium value of 0.22 mNm^?1 independent of Na₂CO₃ concentration (for iC₁₇(EO)₁₃) and to decreasing equilibrium values with increasing alkali concentrations (for C_14–15(PO)₈SO₄). The observed difference in the equilibrium IFT for the two systems suggest that in both systems, the mixed interfacial film is efficient in reducing the dynamic interfacial tension to ultralow transient minima (～10^?3 mNm^?1) but the mixed film soap‐iC₁₇(EO)₁₃ is much less efficient than the mixed film soap‐C_14–15(PO)₈SO₄ in resisting soap diffusion from the interface to the bulk phases. In both systems, the synergism was attributed, in part, to the intermolecular and intramolecular ion–dipole interactions between the soap molecules and the synthetic surfactant as well as to some shielding effect of the electrostatic repulsion between the carboxylate groups by the nearby ethylene oxide (13 EO) and propylene oxide (8 PO) groups in the mixed interfacial monolayer. SDS surfactant showed a much lower synergism relative to iC₁₇(EO)₁₃ and C_14–15(PO)₈SO₄, probably due to the absence of ion–dipole interactions and shielding effect in the mixed interfacial layer at the oil–water interface.     

Functions of Demulsifiers in the Petroleum Industry

There are an increasing number of crude oil fields that are now producing both crude oil and water emulsions; such fields are both onshore and offshore. These emulsions are formed during oil exploitation due to the presence of natural surfactants, such as asphaltenes and resins. These molecules strongly stabilize the water/oil interface and prevent coalescence of water droplets. As water/oil phase separation is necessary before oil transportation and refining, demulsifiers are used to break water-in-oil emulsions. This review presents the crude oil emulsion formation, factors affecting demulsification of crude oil emulsion such as demulsifier chemical structure, water content, partition coefficient (K_P), and demulsifier concentration. This review also covers the kinetics and mechanism of the demulsification process.     

复配表面活性剂对油水界面行为和性质影响的模拟研究

含复配表面活性剂的油田废水是一种多组分复杂体系,研究其中的分子作用关系有助于后续废水处理方案的确定。采用分子动力学(MD)模拟方法建立界面模型,通过定义表面活性剂的关键扭转点及相应的分子夹角、定义协同作用能,结合界面处的密度分布函数等性能模拟和界面张力测试结果,多角度分析两类阴阳离子表面活性剂复配对油水界面特性的影响。结果表明,与含单组分表面活性剂的油水体系相比,复配表面活性剂的相反电荷极性头基间静电吸引作用提高了油水界面稳定性;相较于十二烷基磺酸钠/十六烷基三甲基溴化铵(SLS/CTAB)复配体系,十二烷基硫酸钠/十六烷基三甲基溴化铵(SDS/CTAB)中分子间的协同作用可更好地提高体系的稳定性;当复配表面活性剂的配比为8/10~12/6时的油/水界面稳定效果较优、12/6时稳定性最好。研究结果可为石油开采及油水分离方案的确定提供依据。     

复配表面活性剂对油水界面行为和性质影响的模拟研究

含复配表面活性剂的油田废水是一种多组分复杂体系,研究其中的分子作用关系有助于后续废水处理方案的确定。采用分子动力学(MD)模拟方法建立界面模型,通过定义表面活性剂的关键扭转点及相应的分子夹角、定义协同作用能,结合界面处的密度分布函数等性能模拟和界面张力测试结果,多角度分析两类阴阳离子表面活性剂复配对油水界面特性的影响。结果表明,与含单组分表面活性剂的油水体系相比,复配表面活性剂的相反电荷极性头基间静电吸引作用提高了油水界面稳定性;相较于十二烷基磺酸钠/十六烷基三甲基溴化铵(SLS/CTAB)复配体系,十二烷基硫酸钠/十六烷基三甲基溴化铵(SDS/CTAB)中分子间的协同作用可更好地提高体系的稳定性;当复配表面活性剂的配比为8/10~12/6时的油/水界面稳定效果较优、12/6时稳定性最好。研究结果可为石油开采及油水分离方案的确定提供依据。     

Surface properties of surfactants derived from natural products. Part 1: Syntheses and structure/property relationships—Solubility and emulsification

Several novel and some previously known, mostly sugar-based, surfactants have been synthesized and some of their surface properties have been characterized and compared with those of commercial nonylphenol ethoxylates. The surfactant solubility in water, ethanol, and dodecane was studied. The properties of these compounds as emulsification agents in systems composed of the surfactant with water/isopropyl myristate, water/rapeseed oil, and water/dodecane are presented. The aqueous solubility of the surfactants follows the general trend expected from their hydrophilic-lipophilic balance according to Griffin (HLBG), but it is also clear that the nature of the headgroup and the structure of the nonpolar part affect the solubility in a manner not aptured in the standard HLBG concept. An ester or amine group as the connecting unit between the hydrophile and the hydrophobe produces a more water-soluble surfactant than the corresponding amide derivative. Some effective emulsifiers were found. For instance, the surfactants with a dehydroabietic nonpolar group appear to be promosing emulsifiers. Most sugar-based surfactants were able to form macroemulsions of up to around 2 wt/vol% of oil. The stability of many of these amulsions was very high, extending for months.     

Experimental characterization of emulsion formation and coalescence by nuclear magnetic resonance restricted diffusion techniques

Nuclear magnetic resonance (NMR) is explored as a technique for noninvasively monitoring emulsion droplet formation and destabilization. The method makes use of the fact that the diffusion of oil molecules within oil-in-water emulsion droplets results in attenuation of a coherent magnetic signal that emanates from those molecules. If oil diffusion is limited by the size of the droplet, the shape of a plot of attenuation over time is directly affected by the droplet radius. We use this approach to determine noninvasively the effect of surfactant type, surfactant concentration, pH, and ionic strength on droplet sizes within a 40 wt% octane and water emulsion, stabilized by Tween 20 or β-lactoglobulin (β-Lg). We find that addition of the low-molecular-weight Tween 20 forms finer emulsion droplets than does addition of the protein, and that the Tween 20 emulsion is sensitive to surfactant concentration below a threshold “saturation” concentration. The droplet sizes in β-Lg-containing emulsions increase as pH increases above the isoelectric point and as ionic strength increases. The fact that the NMR technique does not mistake clusters of droplets for single large droplets makes the analysis of these effects unambiguous. We further extend the use of NMR diffusion techniques to monitor the effect of surfactant type, surfactant concentration, and convection on the rate of droplet coalescence. The ability of NMR methods to distinguish between large single droplets and droplet clusters makes it well-suited to monitor coalescence processes independently from flocculation.     

Water solubilization in microemulsions containing amines as cosurfactant

Water-in-oil microemulsions were produced by mixing different combinations of the cationic surfactants cetyltrimethylammonium bromide and cetylpyridinium chloride,n-alkanes (C₅–C₇) and benzene as oils,n-alkylamines (C₆ and C₈) and cyclohexylamine as cosurfactants with water. The influence of chainlength of the alkanes and amines on water solubilization behavior of these systems has been investigated. The solubilization of water in a particular microemulsion is governed by the partitioning of amines among oil, water and interfacial phases, depending on the chainlength and nature of oil and amine, and their interaction with the surfactant. The molar ratio of amine to surfactant at the droplet interface increased with the length of the oil chain. The free energy changes accompanying cosurfactant adsorption at the interface have also been computed.     

Effect of Inorganic Salts on the Aggregation Behavior of AOT at the Air/Water Interface

The aggregation behavior of sodium bis-(2-ethylhexyl)-sulfosuccinate (AOT) at the air/water interface in the absence and presence of inorganic salts was investigated by molecular dynamics simulation. Both monovalent and divalent ions were studied, such as LiCl, NaCl, KCl, MgCl₂ and CaCl₂. It has been proved that these inorganic ions have great influence on the structure of the AOT monolayer and water molecules around its headgroup. In the presence of inorganic salts, AOT molecules are relatively ordered at the interface and water around the headgroups of AOT shows a lower diffusion coefficient compared with the situation without inorganic salts. All the counterions are prone to move toward the headgroups and locate at the interface. Divalent ions have a strong interaction with AOT, thus they affect the aggregation behavior of AOT remarkably.     

Synergistic Effects between Anionic and Sulfobetaine Surfactants for Stabilization of Foams Tolerant to Crude Oil in Foam Flooding

In foam flooding, foams stabilized by conventional surfactants are usually unstable in contacting with crude oil, which behaves as a strong defoaming agent. In this article, synergistic effects between different surfactants were utilized to improve foam stability against crude oil. Targeted to reservoir conditions of Daqing crude oil field, China (45 °C, salinity of 6778 mg L⁻¹, pH = 8–9), foams stabilized by typical anionic surfactants fatty alcohol polyoxyethylene ether sulfate (AES) and sodium dodecyl sulfate (SDS) show low composite foam index (200–500 L s) and low oil tolerance index (0.1–0.2). However, the foam stability can be significantly improved by mixing the anionic surfactant with a sulfobetaine surfactant, which behaves as a foam stabilizer increasing the half-life of foams, and those with longer alkyl chain behave better. As an example, by mixing AES and SDS with hexadecyl dimethyl hydroxypropyl sulfobetaine (C₁₆HSB) at a molar fraction of 0.2 (referring to total surfactant, not including water), the maximum composite foaming index and oil tolerance index can be increased to 3000/5000 L s and 1.0/4.0, respectively, at a total concentration between 3 and 5 mM. The attractive interaction between the different surfactants in a mixed monolayer as reflected by the negative β^s parameter is responsible for the enhancement of the foam stabilization, which resulted in lower interfacial tensions and therefore negative enter (E), spreading (S), and bridging (B) coefficients of the oil. The oil is then emulsified as tiny droplets dispersed in lamellae, giving very stable pseudoemulsion films inhibiting rupture of the bubble films. This made it possible to utilize typical conventional anionic surfactants as foaming agents in foam flooding.     

Solubilisation of water in alkanes using nonionic surfactants

Nonionic surfactants are frequently used as emulsifiers in nonpolar oil + water systems and as solubilisation agents for oil in water, or vice versa. In the latter application the amount of, say, water that can be solubilised in nonpolar oil (to give microemulsion droplets) depends on: (a) the capacity of the micelles to incorporate water; and (b) the fraction of surfactant originally present as micelles. This paper is concerned with the single-phase water-in-oil (W/O) microemulsion regions enclosed by the haze and solubilisation boundaries at the oil-rich end of Shinoda-type phase diagrams. The systems studied contain the nonionic surfactant C₁₂H₂₅(OCH₂CH₂)₅OH (C₁₂E₅), normal alkane (heptane, decane or tetradecane) and water. Critical microemulsion concentrations (cμc) and droplet compositions for w/o microemulsions formed from C₁₂E₅ in alkane have been determined at phase boundaries over a range of temperatures. The results show how the maximum extent of water solubilisation is determined jointly by the cμc and the maximum droplet size for a given temperature. It appears that for larger (microemulsion) droplets, the cμc is determined by temperature rather than by droplet size. However, along part of the haze curves, aggregates form with only small amounts of water (less than four molecules per ethyleneoxy group on the surfactant head groups). For a given temperature, in the small range where either micelles or microemulsion droplets can exist, reverse hydrated micelles have much higher critical micelle concentrations (cmc) than the cμc of the larger microemulsion droplets.     

Edible oil-in-water emulsions stabilized by hydrophile–lipophile balanced sucrose ester

Conventional emulsions are mostly stabilized by surfactants and for stabilization of oil-in-water emulsions the surfactants should be hydrophilic or with HLB numbers larger than seven. In this work, we report that edible oil-in-water emulsions can also be stabilized by surfactants with an HLB value close to seven. With edible sucrose ester C-1807 (HLB no. = 7) as emulsifier and three edible oils (canola oil, olive oil, soybean oil), edible oil-in-water emulsions can be stabilized by C-1807 at concentrations beyond its critical aggregation concentration (CAC). Although monomeric C-1807 behaves as an inferior emulsifier, they assemble to form multilamellar vesicles in water at concentrations higher than the CAC giving a viscoelastic/gel-like aqueous phase which is partly responsible for emulsion stabilization. Specifically, at 2 wt%, high internal phase emulsions (HIPEs) with ϕ_o = 0.75 can be obtained, which are stable against cooling–heating cycles between 5 and 30°C during storage. The vesicles disperse in the aqueous lamellae surrounding the oil droplets, which together with the viscoelastic/gel-like continuous phase prevents them from flocculation and coalescence.     

Influence of clay addition on the properties of olive oil in water emulsions

The behaviour of olive oil-in-water emulsions (O/W) was studied in the presence of smectite particles. The distribution of these particles in the emulsions and the effect of their interaction with the surfactant on the stability of the emulsions were investigated. Whereas the variation of surfactant and/or clay content did not seem to affect the nature of the emulsion, it had a significant influence on emulsion stability. This observation led to two main assumptions on the distribution of clay particles within the emulsion, either exclusively in the continuous phase, or also at the oil-water interface.In the absence of clay, the variation of surfactant concentration (from 0 to 17% (w/w)) allowed to distinguish 3 domains. In the first concentration domain (0–4.2%) emulsions stability increased with the content of surfactant. Within the second domain (4.2–8.5% (w/w)), a slight decrease in stability was observed due to flocculation by depletion. For surfactant concentrations equal or higher than 8.5% (3rd domain), emulsion stability increased sharply, probably due to the development of interactions between surfactant molecules as they came closer to their gelling concentration. The effect of clay addition to the aqueous phase (up to 10% (w/w)) on the physicochemical properties of the studied emulsions was assessed from stability, drop size, interfacial tension, rheological and acido-basic analyses. A model based on the location of clay particles either in the bulk or at the interface could be proposed, in which clay particles would interact with surfactant molecules in the bulk phase, and form a mechanical barrier around the oil droplets, thus increasing emulsion stability.     

One-Step Synthesis of W/O and O/W Emulsifiers in the Presence of Surface Active Agents

The main goal of this study was to describe the method of the synthesis of the dodecyl-, tetradecyl-, hexadecyl- and octadecyl-propylene glycol emulsifiers in the presence of selected anionic and nonionic surfactants. Acyl propylene glycol emulsifiers were produced by esterification of propane–1,2-diol (propylene glycol, PG) with C_12:0–C_18:0 fatty acids in the presence of anionic sodium dodecyl sulfate (SDS) and nonionic-poly(ethylene glycol) monolaurate (PEGML). The presence of SDS and PEGML in the reaction system caused microemulsion formation. Depending on the structure and amount of the surfactant in the system reactions proceeded at different rates and with different efficiency levels. The esterification of propylene glycol carried out under applied conditions causes products with the desired contents of propylene glycol monoesters (MAPG) to be obtained in a one-step reaction. Knowledge of the reaction kinetics creates the possibility to program the composition and properties of the synthesized emulsifiers. The interaction of nonionic, lipophilic MAPG with anionic, hydrophilic SDS or nonionic, hydrophilic PEGML influences the hydrophile–lipophile balance (HLB) values of the products which may be used to stabilize water-in-oil (W/O) and oil-in-water (O/W) emulsions. Use of the synthesized compounds allows stable emulsions to be prepared which include the following vegetable fats in the oil phase: mango oil, palm oil, shorea butter and hydrogenated soybean oil.