Interfacial dilational properties of tri-substituted alkyl benzene sulfonates at air/water and decane/water interfaces

The effect of aromatic side chains on the dilational rheological properties of N-acyltaurate amphiphiles at water-decane interfaces

To elucidate the effect of aromatic side chains on dilational rheological properties of N-acyltaurate amphiphiles at the decane-water interface, the interfacial rheological properties of sodium N-2-(2-naphthoxy)-tetradecanoyltaurinate (12+N-T) and sodium N-2-(p-butylphenoxy)-tetradecanoyltaurinate (12+4B-T) were investigated utilizing the drop shape analysis method. The effects of adsorption time, interfacial pressure, oscillating frequency, and bulk concentration on the interfacial dilational modulus and phase angle were explored. The results show that the 12+4B-T molecule with a longer hydrophobic chain shows a higher ability for reducing the interfacial tension (IFT). In addition, the interfacial films of both 12+N-T and 12+4B-T are dominated by diffusion exchange at high concentrations. The rigidity of molecules controls the diffusion exchange at low concentrations, while the molecular hydrodynamic radius determines the diffusion exchange at high concentrations. Thus, at low concentrations, the stronger intermolecular interaction between 12+4B-T molecules results in higher dilational modulus values than 12+N-T. When approaching the CMC (critical micelle concentration) value, the rapid diffusion exchange of 12+4B-T between the sublayer micelles and the interface causes a significant decrease in the dilational modulus, while the relatively rigid structure of 12+N-T enables a higher dilational modulus than 12+4B-T. What's more, the longer hydrophobic chain allows 12+4B-T molecules to escape from the interface more easily, resulting in a higher phase angle at low concentrations. However, the diffusion exchange of 12+4B-T is slower than that of 12+N-T, which results in lower phase angles for 12+4B-T than 12+N-T at high concentrations. In general, the introduction of a rigid naphthalene ring in the molecular structure gives the interfacial film greater strength at high concentration. The research results in this paper provide a new technique for the strength regulation of interfacial surfactant adsorption films.

Dilational Rheology of Extended Surfactants at the Air/Water and Oil/Water Interfaces: Effect of Propylene Oxide Group Numbers

In this paper, the interfacial properties of extended surfactants with different oxypropylene (PO) groups were comprehensively investigated by using interfacial dilational rheology. The differences in molecular orientation, spatial configuration, and relaxation process were compared at the gas-water interface and oil-water interface. The influences of the PO groups on the interface viscoelasticity were analyzed, providing important theoretical support for the wide application of extended surfactants. Experimental results show that the lower number of PO groups in extended surfactants does not cause differences in their presence states on the interface; however, once it increases, the longer PO segment will spiral up in the direction perpendicular to the interface, forming a spatial configuration like a thin cylinder. Compared with air, the PO group has better solubility in the oil phase. The chain segment can still maintain a helical extension from the beginning to the end as a result. However, the upper layer of the thin cylinder will collapse to a certain extent at the surface. Moreover, the orientation of the hydrophobic side has a dynamic process of "tilting to upright" with the increase of adsorption amount or in response to interfacial dilation and compression. The increase of PO number or the insertion of oil molecules has little effect on dilational modulus, and the interfacial film strength is generally relatively low. That is to say, the better emulsifying and solubilizing ability of PO-containing extended surfactants may be more attributed to the matching steric effect at interface or better packing action in bulk phase than to higher film strength.

The Interfacial Dilational Rheology Properties of Betaine Solutions: Effect of Anionic Surfactant and Polymer

Interfacial dilational rheology is one of the important means to explore the interfacial properties of adsorption films. In this paper, the interfacial rheological properties of the mixed system of sulfobetaine ASB with a linear alkyl group and two anionic surfactants, petroleum sulfonate (PS) and alkyl polyoxyethylene carboxylate (AEC), were investigated by interfacial dilational rheology. The effect of the introduction of polymer hydrophobically modified polyacrylamide (HMPAM) on the interfacial properties of the mixed system was analyzed. In this experiment, the surfactant solution was used as the external phase and n-decane was used as the internal phase. A periodic sinusoidal disturbance of 0.1 Hz was applied to the n-decane droplets, and the changes of parameters such as droplet interfacial tension and interfacial area were monitored in real time with the help of a computer. The results show that the betaine ASB molecule responds to the dilation and compression of the interface through the change of ion head orientation, while the feedback behavior of petroleum sulfonate PS and AEC molecules embedded with oxygen vinyl groups in the molecule is diffusion and exchange between the interface and the bulk phase. Therefore, the interface film formed by ASB alone is higher, and the film formed by PS and AEC molecules alone is relatively lower. After adding two kinds of anionic surfactants to the betaine system, the ionic head of PS or AEC molecules will be attached to the positive center of the hydrophilic group of ASB molecules by electrostatic attraction and no longer adsorb and desorb with the interface deformation. The interfacial rheological properties of the compound system are still dominated by betaine, with higher dilational modulus and lower phase angle. When a small amount of HMPAM is added, or the content of hydrophobic monomer AMPS in the bulk phase is low, the intermolecular interaction at the interface is enhanced, the slow relaxation process is intensified, and the interfacial film strength is increased. As the content of AMPS further increases, hydrophobic blocks and surfactant molecules will form interfacial aggregates similar to mixed micelles at the oil-water interface, which will regulate the properties of the film by affecting the adsorption of surfactants at the interface. As long as the interfacial tension is the same, the properties of the interfacial film are the same. Based on the colloid interface science and the background of enhanced oil recovery, this study provides a reference for the field application of chemical flooding formulations.

The Study of Interfacial Adsorption Behavior for Hydroxyl-Substituted Alkylbenzene Sulfonates by Interfacial Tension Relaxation Method

In order to explore the interface adsorption mechanism of hydroxyl-substituted alkylbenzene sulfonates, the interfacial tension relaxation method was used to investigate the dilational rheology properties of sodium 2-hydroxy-3-octyl-5-octylbenzene sulfonate (C₈C₈OHphSO₃Na) and sodium 2-hydroxy-3-octyl-5-decylbenzene sulfonate (C₈C₁₀OHphSO₃Na) at the gas-liquid interface and oil-water interface. The effect of the length of the hydroxyl para-alkyl chain on the interfacial behavior of the surfactant molecules was investigated, and the main controlling factors of the interfacial film properties under different conditions were obtained. The experimental results show that for the gas-liquid interface, the long-chain alkyl groups adjacent to the hydroxyl group in the hydroxyl-substituted alkylbenzene sulfonate molecules tend to extend along the interface, showing strong intermolecular interaction, which is the main reason why the dilational viscoelasticity of the surface film is higher than that of ordinary alkylbenzene sulfonates. The length of the para-alkyl chain has little effect on the viscoelastic modulus. With the increase in surfactant concentration, the adjacent alkyl chain also began to extend into the air, and the factors controlling the properties of the interfacial film changed from interfacial rearrangement to diffusion exchange. For the oil-water interface, the presence of oil molecules will hinder the interface tiling of the hydroxyl-protic alkyl, and the dilational viscoelasticity of C₈C₈ and C₈C₁₀ will be greatly reduced relative to the surface. The main factor controlling the properties of the interfacial film is the diffusion exchange of surfactant molecules between the bulk phase and the interface from the beginning.

The Synergistic Effects between Sulfobetaine and Hydrophobically Modified Polyacrylamide on Properties Related to Enhanced Oil Recovery

In order to explore the mechanism responsible for the interactions in the surfactant-polymer composite flooding and broaden the application range of the binary system in heterogeneous oil reservoirs, in this paper, the influences of different surfactants on the viscosity of two polymers with similar molecular weights, partially hydrolyzed polyacrylamide (HPAM) and hydrophobically modified polyacrylamide (HMPAM), were studied at different reservoir environments. In addition, the relationship between the surfactant-polymer synergistic effects and oil displacement efficiency was also investigated. The experimental results show that for HPAM, surfactants mainly act as an electrolyte to reduce its viscosity. For HMPAM, SDBS and TX-100 will form aggregates with the hydrophobic blocks of polymer molecules, reducing the bulk viscosity. However, zwitterionic surfactant aralkyl substituted alkyl sulfobetaine BSB molecules can build "bridges" between different polymer molecules through hydrogen bonding and electrostatic interaction. After forming aggregates with HMPAM molecules, the viscosity will increase. The presence of two polymers all weakened the surfactant oil-water interfacial membrane strength to a certain extent, but had little effect on the interfacial tension. The synergistic effect of the "bridge" between HMPAM and BSB under macroscopic conditions also occurs in the microscopic pores of the core, which has a beneficial effect on improving oil recovery.

How to Regulate the Migration Ability of Emulsions in Micro-Scale Pores: Droplet Size or Membrane Strength?

Micro visualization has become an important means of solving colloid and interface scientific problems in enhanced oil recovery. It can establish a relationship between a series of performance evaluations of an oil-water interface under macroscopic dimensions and the actual application effect in confined space, and more truly and reliably reflect the starting and migration behavior of crude oil or emulsion in rock pores. In this article, zwitterionic surfactant alkyl sulfobetaine (ASB) and anionic extended surfactant alkyl polyoxypropylene sulfate (A145) were employed as flooding surfactants. The macroscopic properties of the surfactant solutions, such as the oil-water interfacial tension (IFT), the interfacial dilational rheology and the viscosity of crude oil emulsions, have been measured. At the same time, we link these parameters with the oil displacement effect in several visual glass models and confirm the main factors affecting the migration ability of emulsions in micro-scale pores. The experimental results show that ASB reduces the IFT through mixed adsorption with crude oil fractions. The flat arrangement of the large hydrophilic group of ASB molecules enhances the interactions between the surfactant molecules on the oil-water interface. Compared with sulfate, betaine has higher interfacial membrane strength and emulsion viscosity. A145 has a strong ability to reduce the IFT against crude oil because of the larger size effect of the PO chains at the oil side of the interface. However, the membrane strength of A145 is moderate and the emulsion does not show a viscosity-increasing effect. During the displacement process, the deformation ability of the front emulsions or oil banks is the main controlling factor of the displacement efficiency, which is determined by the membrane strength and emulsion viscosity. The strong interfacial membrane strength and the high emulsion viscosity are not conducive to the migration of droplets in pore throats and may result in low displacement efficiency.

Effect of Added Tetraalkylammonium Counterions on the Dilational Rheological Behaviors of N-Cocoyl Glycinate

Ion specific effect, which is also known as Hofmeister effect, has been reported in numerous systems including ionic surfactant aggregates. Acyl amino acid surfactants have attracted growing attentions in the field of novel surfactants research due to their environmentally benign characteristics. The objective of this study was to investigate the effect of different salts containing NH₄⁺ and tetraalkylammonium (TAA⁺), where alkyl = methyl (TMA⁺), ethyl (TEA⁺), and propyl (TPA⁺), cations on the dilational rheological properties of interfacial film are stabilized by potassium N-cocoyl glycinate (KCGl). The interfacial behaviors were studied using oscillating drop shape analysis method. The interfacial tensions (IFTs) and dilational rheological parameters results illustrate that KCGl in the presence of salts has better interfacial activity and stronger intermolecular interaction, indicating that added cations contribute to denser molecular packing at oil-water interface. Ion specific effects were observed in the system. Among the cations, KCGl shows highest dilational modulus in the presence of NH₄⁺. The overall interaction between cations and headgroups of KCGl decreases in the sequence NH₄⁺ >TMA⁺ >TEA⁺ ≈TPA⁺, which follows Hofmeister series. The increasing hydrophobicity of TAA⁺ prevents the interaction between cations and KCGl's headgroup, and therefore prevent amphiphiles from packing closely at interface. The results present a theoretical origin for useful application of KCGl in cosmetics, petroleum and daily chemical industries.

A comparative study on the interface tension and interface dilational rheological properties of three sodiumN-acyl aromatic amino acid surfactants

Interface dilational rheology is useful for understanding and exploring the role of interface phenomena. However, relatively few studies have been conducted on the interface dilational rheological properties of N-acyl aromatic amino acid surfactants. Herein, surface tension and the dynamic interface tension and dilational rheological properties of three surfactants, namely, sodium N-lauroyl phenylalaninate (SLP), sodium N-lauroyl tyrosinate (SLTy), and sodium N-lauroyl citrate (SLTr) were investigated. The results show that the order of critical micelle concentration, which includes the surface tension at the critical micelle concentration, minimum area per surfactant molecule, and interfacial tension, was SLTr < SLTy < SLP. At a low surfactant concentration, the three surfactants exhibited a low-viscosity interfacial elastic film at the n-decane/water interface. The dilational modulus increased and the phase angle decreased with increase in frequency. However, the order of the dilational modulus was SLP < SLTy < SLTr, while the order of the phase angle change was SLTr < SLTy < SLP at the same frequency. With increase in surfactant concentration, the dilational modulus of SLP and SLTy increased and then decreased after a maximum value; however, the dilational modulus plot of SLTr demonstrated two maxima.

Interface dilational rheology is useful for understanding and exploring the role of interface phenomena.

Interfacial rheological behaviors of amphiphilic sodium cholesteryl glycylglycine

The present study was conducted to investigate the effects of the strong van der Waals interaction and sterol skeleton of surfactants on their interfacial rheological behaviors by comparing the interfacial properties of sodium cholesteryl glycylglycine (Chol-GG-Na) and sodium lauryl glycylglycine (C12-GG-Na) at the oil-aqueous interface. The interfacial dilational rheological experiment results indicate a significant increase in the interfacial activity and intermolecular interaction with the introduction of the cholesteryl group. Therefore, a compact interfacial layer with a remarkably high dilational modulus was obtained with the adsorption of Chol-GG-Na. The cholesteryl group also has a significant impact on the dynamic processes such as it slows down the motion of the molecules due to which the diffusion exchange between the bulk and the interface decreases. Besides, the rigid skeleton makes rearrangement and conformation adjustment difficult. These impacts become more pronounced when the adsorption layer approaches a close and ordered arrangement, which has been confirmed by the relaxation measurements. The reported results provide a theoretical foundation for the potential applications of cholesteryl-based surfactants in the food, pharmaceutical, cosmetic and petroleum industries.

Pilot Performance of Chemical Demulsifier on the Demulsification of Produced Water from Polymer/Surfactant Flooding in the Xinjiang Oilfield

Purification of produced water (PW) from polymer/surfactant flooding is a challenge for the petroleum industry due to the high emulsion stability. Demulsification using chemical demulsifiers has been expected to be an effective way to treat PW. In this paper, five cationic (branched quaternary ammonium chloride) and four nonionic (copolymer of propylene oxide and ethylene oxide) demulsifiers with different molecular weights were employed to test their respective demulsification performance in the treatment of PW from polymer/surfactant flooding. The cationic demulsifiers, in general, exhibited better performance than the nonionic ones and one cationic demulsifier (CP-1) exhibiting the best demulsification efficiency was further employed for a pilot experiment in the Xinjiang Oilfield. The oil content of PW could be successfully reduced from 128~7364 to less than 10 mg/L with a dosage of CP-1 for 350 mg/L and polyaluminum chloride (PAC, 30% w/w Al2O3) for 500 mg/L under ambient temperature (14~22 °C). At the same time, partially hydrolyzed polyacrylamide (HPAM) was removed from 176.9~177.1 to 2.8~3.9 mg/L while petroleum sulfonate was not removed too much (from 35.5~43.8 to 25.5~26.5 mg/L). The interfacial rheology analysis on simulated PW from HPAM/petroleum sulfonate flooding revealed that the addition of CP-1 led to a significant increase of the oil-water interfacial tension (from 7 to 15~20 mN/m) and zeta potential (from −32.5 to −19.7 mV). It was, thus, assumed that the decreased net charge on the dispersed oil droplets surface and weakened oil/water film due to the formation of complex between the cationic demulsifier and HPAM may have facilitated the destabilization of the emulsion. The result of this study is useful in better understanding the demulsification processes as well as selecting suitable demulsifiers in the treatment of PW from polymer/surfactant flooding.

Achieving foaming control smartly: pre-solubilized flavor oil serves as an in situ homogeneous defoamer

In the wide application of aqueous foam, creating abundant foam and processing appropriate foaming control are both essential, depending upon the actual situation; the latter process is not only harder to achieve, but also more complicated to comprehensively understand on the molecular level. In this paper, a type of natural flavor oil, carvone, was solubilized in a micelle solution of sodium dodecyl sulfate (SDS) to study the effect on the foaming properties. The foamability and foam stability of the swollen micelle solutions were experimentally characterized, and the molecular behavior of the surfactant and oil molecules before, during and after the foaming process were investigated. It was found that the solubilized carvone co-adsorbed with SDS at the gas/water interface and caused a prominent effect on the foam film stability in several approaches, thereby making the flavor oil a possible foam controller that would not inhibit foam formation, but could eliminate foam efficiently once foam was undesired. Interestingly, it was found that the release of flavor in the foaming process was promoted. Detailed discussion of the interfacial behavior of carvone and the effect on the foaming properties of surfactants in different stages of foam may provide a theoretical foundation for exploring green and smart approaches in achieving foaming control.

Interfacial rheological behaviors of inclusion complexes of cyclodextrin and alkanes

The transformation of cyclodextrins (CDs) and alkanes from separated monomers to inclusion complexes at the interface is illustrated by analyzing the evolution of interfacial tension along with the variation of interfacial area for an oscillating drop. Amphiphilic intermediates are formed by threading one CD molecule on one alkane molecule at the oil/aqueous interface. After that, the amphiphilic intermediates transform into non-amphiphilic supramolecules which further assemble through hydrogen bonding at the oil/aqueous interface to generate a rigid network. With the accumulation of supramolecules at the interface, microcrystals are formed at the interface. The supramolecules of dodecane@2α-CD grow into microrods which form an unconsolidated shell and gradually cover the drop. However, the microcrystals of dodecane@2β-CD are significantly smaller which fabricate into skin-like films at the interface. The amphiphilic intermediates during the transformation increase the feasibility of self-emulsification and the skin-like films enhance the stability of the emulsion. With these unique properties, CDs can be promising for application in hydrophobic drug delivery, food industry and enhanced oil recovery.

Interfacial Properties and Monolayer Collapse of Alkyl Benzenesulfonate Surfactant Monolayers at the Decane-Water Interface from Molecular Dynamics Simulations

The molecular structure of a surfactant molecule is known to have a great effect on the interfacial properties and the type of nanostructures formed. In this work, we have performed molecular dynamics simulations on six isomers of an alkyl benzenesulfonate surfactant to investigate the effect of the degree and position of aromatic substitution on the interfacial properties and on the collapse of the surfactant monolayer at a decane-water interface. The surface pressure of the monolayers was shown to increase with increasing surface coverage, until some of the monolayers become mechanically unstable and form large undulations. Shifting the primary alkyl chain of the surfactant from the para to the meta position was found to significantly affect the orientation of the surfactant head groups, while the attachment position of the benzene ring along the primary alkyl chain plays a greater role in the orientation of the surfactant tails. In general, to the extent considered in this work, our results suggest that additional alkyl substitution and meta substitution of the primary alkyl chains increase both the effectiveness and efficiency of the surfactants, and accelerate the onset of monolayer collapse. The interface was found to consist of an inner Helmholtz layer of partially dehydrated counterions in contact with the surfactant head groups, an outer Helmholtz layer of hydrated counterions, and a diffuse layer. The di- and trisubstituted surfactants formed nearly spherical swollen micelles encapsulating pure decane, which effectively solubilizes decane in water as a microemulsion. The monosubstituted surfactants formed elongated buds that protrude from the interface, but did not detach from the monolayer. To our knowledge, the role of aromatic substitution on interfacial properties has not been investigated by molecular simulations previously. The results from this work could provide insights to design improved surfactants by exploiting aromatic substitution to encapsulate material for drug delivery and other applications.

Surface dilational rheological properties in the nonlinear domain

The interfacial tension response to dilational deformation of interfacial area exhibits a (more or less) nonlinear behavior, depending on the amplitude of the deformation. Studies of such observable interfacial properties in the nonlinear domain suggest valuable information about the two-dimensional microstructure of the interfacial layer, as well as about the structure time-evolution. In this article, the emphasis is centered on the available mathematical methods for quantitatively analyzing and describing the magnitude and the characteristics of the nonlinear interfacial viscoelastic properties. Specifically, in periodic oscillation experiments the nonlinear behavior can be represented by the combination of a linear part (the surface dilational modulus), with an additional complementary Fourier analysis parameterizing the nonlinearity. Also asymmetric Lissajous plots, of interfacial tension versus deformation, are useful tools for expanding the response nonlinearity into four distinct components relevant to significant points of the cyclic loop. In connection with the mathematical methods, nonequilibrium thermodynamic formulations provide a powerful theoretical framework for investigating the interfacial dynamic properties of multiphase systems. Experimental results for adsorption layers of complex components, available in the literature, show notable nonlinear interfacial viscoelastic behavior. In particular in this review, data are illustrated for solutions of polymers and of polyelectrolyte/surfactant complexes. The observed nonlinear findings reveal formation of complexes, patches, and other different interfacial structures.

Surface Dilational Properties of Sodium 4-(1-methyl)-Alkyl Benzene Sulfonates: Effect of Alkyl Chain Length

The dilational properties of absorbed film of three sodium 4-(1-methyl)-alkyl benzene sulfonates at the air-water interface have been investigated by drop shape analysis method. The influences of time, dilational frequency and surfactant bulk concentration on surface dilational modulus and phase angle have been expounded. The nature of interfacial film depends on the molecular structure of surfactants. For 2Φ-14 and 2Φ-16, the diffusion-exchange process controls the dilational properties and the film shows viscoelastic character. As an increase of the hydrophobic chain, the dilational modulus of 2Φ-18 is independent on applied frequency in the studied bulk concentration except for 1 × 105 mol/L, which indicates the adsorbed layer behaves nearly purely elastic. Furthermore, the phase angle of 2Φ-14 and 2Φ-16 are remarkably higher than those of 2Φ-18, confirming that the presence of strong interactions between hydrophobic chains of 2Φ-18. Best agreements with the experimental data have been obtained from the curves of dilational modulus vs. surface pressure.

Interfacial Dilational Properties of Novel Crosslinking Phenol-Amine Resin Block Polyether Demulsifiers at Decane-Water Interfaces

Nine novel crosslinking phenol-amine resin block polyether (PARPEmn) as demulsifier were synthesized for Shengli Oil Field. And the dilational rheological properties of absorbed film of nine different structural demulsifiers were investigated by longitudinal wavesmethod (the Langmuir trough-Wilhelmy plate technique) at the decane-water interfaces. The results show that demulsifier concentration is an important factor in controlling the dilational properties of adsorption layer. The dilational elasticity for all demulsifiers appeared a maximum value with the increasing concentration. Most important of all, the relations between interface dilational properties and demulsifier structures have been studied. It demonstrates that the interfacial dilational modulus increase with the increase the HLB value of demulsifiers.