Increasing Surfactant Concentration Research Articles

Diversity Variation of Silica-Scaled Chrysophytes Related to Differences in Physicochemical Variables in Estuaries of Rivers in an Arctic Watershed

The present study examined the taxonomic diversity of silica-scaled chrysophytes in the estuaries of the Arctic watershed of Yakutia in the context of global climate change, as these aquatic organisms are highly sensitive to environmental changes. Previously, 41 species of silica-scaled chrysophytes were recorded in the waters of Yakutia. In the present study, we supplemented this list with 55 species. We observed a high species richness (82 taxa) of silica-scaled chrysophytes in the study area. Of these, eight species were recorded in the waters of Russia for the first time. At present, the study area represents the northernmost habitat for most species observed during the study. The diversity of silica-scaled chrysophytes in Arctic rivers is comparable to or even greater than the diversity of chrysophycean flora at the middle latitudes. Most of these chrysophytes are represented by polyzonal and ubiquitous species. During 2008–2010, we noted increased relative numbers of boreal species in northern waters compared with data obtained during the previous 30 years. Overall, the species richness of silica-scaled chrysophytes in the studied rivers increased with increase in water transparency, temperature, and magnesium ion concentration, but decreased with increase in surfactant concentration. The origin of samples from a certain river; distance of the sampling site from the estuary; water temperature, transparency, and colour; and concentration of carbon dioxide, magnesium ions, total iron, surfactants, and oil products affect the species composition of silica-scaled chrysophytes in the study area. Our findings are fundamental to evaluate the current status of Arctic aquatic microflora and its further monitoring in the context of anthropogenic and climatic impacts.

Influence of interfacial, thermodynamic and hydrophobic parameters on Acid Red 57 removal by ionic micellar flocculation

ABSTRACT Most dyes are complex organic molecules that are highly resistant to degradation and may cause severe damage to live organisms and photosynthetic activities. In this respect, the aim of the present study was to assess the influence of interfacial, thermodynamic and hydrophobic parameters on Acid Red 57 removal from aqueous media by ionic micellar flocculation using surfactants sodium dodecanoate (C12), sodium tetradecanoate (C14) and sodium hexadecanoate (C16). The results demonstrate that an increase in the hydrophobic nature of the surfactant provokes different Krafft (Tkrafft) temperature and critical micelle concentration behaviors, and the greater the hydrophobicity the higher the solubilization temperature and lower the concentration needed for micelle formation. It was also found that long-chain surfactants cause an increase in the area of the polar part of the surfactant and change the micelle shape from lamellar (C12, C14) to cylindrical (C16), interfering in the solubilization capacity of the micelles. Micelle diameter determination aimed at demonstrating that the dye is solubilized inside the micelles via hydrophobic interactions. The dye removal tests showed that an increase in surfactant concentration improves process efficiency, surfactant C12 exhibiting the best dye removal indices (around 90%). Thermodynamic parameters showed that ionic micellar flocculation is exothermic and non-spontaneous.

Using niobium/BDD anode-based multi-cell flow reactor for the electrochemical oxidation of methyl paraben in the presence of surfactants

This study reports the electrochemical oxidation of methyl paraben (MeP) in synthetic wastes in the presence of surfactants using boron-doped diamond (BDD) anode and the interfering effect of the surfactants in MeP removal. The selected surfactants (cationic, anionic, and neutral) were used at critical micellar concentrations (CMC) and below with measurements performed to evaluate the removal rates of MeP and total organic carbon (TOC). The effects of current density (15, 30, and 45 mA cm−2), surfactant concentration, and initial pH on the efficiency of the electrochemical oxidation process were analyzed. At low concentrations, the interfering effect of the anionic surfactant (sodium dodecyl sulfate - SDS) was greater than that of the cationic surfactant (hexadecyltrimethylammonium bromide - CTAB). The complete mineralization of MeP + SDS was achieved at 45 mA cm−2 in 2 h; this was attributed to the generation of persulfate radicals at current densities higher than 15 mA cm−2. Genapol C-100 (Genapol) exerted less interference during the mineralization of MeP + Genapol compared to the systems containing other surfactants at CMC. MeP removal was favored by the use of a basic medium. The increase in surfactant concentration decreased the efficiency of MeP and TOC removal due to the formation of micelles and the intensity of MeP-surfactant interactions, apart from the increase in organic load in the system. CTAB interacted more with the ionic form of MeP in the basic medium compared to the other surfactants. All these factors influenced the mineralization of organic compounds in the systems.

Robustness of surfactant-laden latex films

Despite the growing popularity of latex inks in the inkjet printing industry, little is known about the influence of additives present in the ink mixtures on the robustness of the latex films. Here, we investigate the influence of a non-ionic surfactant, Dynol 607, on the abrasion robustness of a water-based latex film. For fixation temperature below the minimal film formation temperature (MFFT), we observe an improvement of robustness of the film with increasing surfactant concentration due to the improved film coalescence. However, for temperatures exceeding the MFFT, Dynol clearly has a negative impact on the abrasion robustness. Using AFM in the PeakForce tapping mode we have demonstrated that the surfactant forms ultra-thin surfactant layers at the top of the latex film. Force spectroscopy performed with the colloidal probes showed that these layers can increase the adhesion between the film and abrasive material leading to decreased abrasion robustness. However, other effects such as: macroscopic corrugation of the film or the surfactant layer between latex film and the substrate that may have influence on the mechanical performance of the film, were also identified. Our research showcases that mechanical robustness of latex films is affected by surfactant in various ways, which are poorly understood, even though surfactants are commonly used in latex ink formulations.

Two-dimensional colloidal particle assembly in ionic surfactant solutions under an oscillatory electric field

Assembling colloidal particles under oscillatory electric field (OEF) has become an emerging bottom-up technique to synthesize advanced materials and fabricate micro/nano devices. Surfactants have often been used in colloidal dispersions to improve their stability. However, the precise role of surfactants in particle assembly processes under OEF is unknown. Here, we systematically study the effects of ionic surfactants on the colloidal particle assembly process subject to a fixed OEF, by using an anionic surfactant (sodium dodecyl sulfate) and a cationic surfactant (cetyltrimethylammonium bromide). In the concentration range below the critical micelle concentration (CMC), the particles tend to form three different aggregate structures, including randomly close-packed, hexagonally close-packed crystals, and randomly non close-packed structures. In the concentration range at CMC and above, the particles cannot assemble into any aggregate structures under the given OEF. With increasing surfactant concentration, the average interparticle separation distance within the aggregate can be regulated in a wide range. We qualitatively interpret the observed variation of particle assembly behaviors in different surfactant solutions based on the particle/particle interaction energy, implying that the repulsive electric double-layer interaction is significantly enhanced with increasing ionic surfactant concentration and hinders the particles approaching close to the high-energy barrier. These results suggest that the particle aggregate structure and interparticle separation distance of the two-dimensional colloidal assembly can be manipulated by controlling the ionic surfactant concentration according to the requirements of practical applications.

Micellization of Rhamnolipid Biosurfactants and Their Applications in Oil Recovery: Insights from Mesoscale Simulations.

The dissipative particle dynamics (DPD) mesoscopic method is used to investigate the self-assembly of rhamnolipid congeners and their aggregation behaviors with paraffins including nonane and pentadecane. The coarse-grained force field is parameterized by combining molecular dynamics (MD) simulations, COSMOtherm calculations, and available experimental data. This model reproduces the vesicular formation of α-l-rhamnopyranosyl-β-hydroxydecanoyl-β-hydroxydecanoate (Rha-C10-C10) reported by all-atom MD simulations. The vesicle composed of Rha-C10-C10 is found to be most stable at a surfactant concentration of 100-146 mM based on asphericity analysis. The architecture of rhamnolipid congeners affects the morphology of their aggregates. Di-rhamno-di-lipidic dRha-C16-C16 forms vesicles with a thicker unilamellar layer of 3.2 nm. Rha-C16-C16 forms vesicles at a lower concentration of 70 mM, but the enclosed water space collapses when the surfactant concentration increases. dRha-C10-C10 forms wormlike micelles, which agglomerate into a torus and interconnected network at higher concentrations. In the presence of alkane molecules, dRha-C10-C10 maintains its wormlike micellar morphology with alkane molecules wrapped inside the aggregates. For Rha-C10-C10, Rha-C16-C16, and dRha-C16-C16, nonane molecules are distributed in the hydrophobic subdomain formed by rhamnolipid molecules. Spherical vesicles are formed at a surfactant concentration of 50 mM and then develop into ellipsoidal vesicles when the concentration increases to 125 mM. When mixed with pentadecane, the alkane molecules are aggregated and surrounded by surfactants forming a core-shell structure at a low surfactant concentration of 20 mM. At higher alkane and surfactant concentrations, the morphologies develop into disk micelles, wormlike micelles, and vesicles, with pentadecane molecules being distributed and packed with rhamnolipids. The obtained simulation results suggest that these biosurfactants have potential as environmental remediation agents.

Molecular dynamics study on emulsified oil droplets with nonionic surfactants

The stability of heavy crude oil is closely related to the netlike structure formed by the aggregation of asphaltene and resin molecules inside the oil droplets, and the aggregation is too complex to accurately obtain the microstructure of these molecules experimentally. In this paper, molecular dynamics (MD) simulation was performed to investigate the structure of emulsified oil droplets on the molecular level. The simulation results showed: (i) The stacking structure of asphaltene and resin molecules form the netlike structure of the oil droplet, and it is also considered as the main reason of high stability and viscosity of heavy crude oil. (ii) When nonionic surfactants were introduced, some of them can adsorb to the surface of oil droplet and change its hydrophilicity; others can enter the interior of the oil droplets and destroy the stacking structure of asphaltene or resins inside the oil droplet. The decreased viscosity of emulsified heavy oil in the present of surfactants attributed to the increase of hydrophilicity on the oil drop surface and the damage of stacking structure inside the oil drops. (iii) the steered molecular dynamics (SMD) simulation proved that the mechanical properties of emulsified heavy oil droplet become easier to be destroyed with the increase of surfactant concentration, and it indicates that nonionic surfactant is beneficial to promote demulsification and viscosity reduction of crude oil.

Nonionic surfactant stabilized polytetrafluoroethylene dispersion: Effect of molecular structure and topology

Polytetrafluoroethylene (PTFE) is a kind of fluoropolymer with many critical applications. Nonionic surfactant stabilized concentrated PTFE aqueous dispersions are widely used to prepare corresponding products via dipping, spraying, spinning, or film casting, as these surfactants exert a negligible effect on the properties of the products. Although many nonionic surfactants have been used to stabilize PTFE dispersions in industry, the effects of molecular structure and topology are not well-documented; thus, currently, there is no basis for selecting or designing suitable novel surfactants to enhance dispersion stability. In this work, five nonionic surfactants with different topological structures including Tween 20, Tween 60, Tween 80, Brij L23, and Brij O20, were used to prepare concentrated PTFE dispersions. The variation of particle morphology before and after concentration was examined by scanning electron microscopy, and the static stability of the dispersions was quantitatively and objectively characterized using a Turbiscan analyzer based on multiple light scattering. Then the effect of surfactant molecular structure and topology on dispersion stability was discussed. We found that, after the enrichment process, the PTFE microspheres were tightly packed, and some were deformed. Brij surfactants which bears a linear hydrophilic oxyethylene (EO) chain can form a thicker hydration layer on the surface of PTFE particles than those of Tween surfactants which contains a branched hydrophilic EO chain. Accordingly, PTFE dispersions with Brij surfactants show better static stability. Moreover, in comparison with the saturated hydrophobic tail, the unsaturated hydrophobic chain is more flexible, so it can adhere to the surface of PTFE particles better, improving the stability. In addition, the increase of surfactant concentration contributes to the increase of micelles density and viscosity of the bulk dispersion, which can also enhance the stability. These findings are beneficial to design or choose suitable surfactants for high stability and high-quality concentrated PTFE dispersions.

Temporally persistent networks of long-lived mixed wormlike micelles of zwitterionic and anionic surfactants

Rheometry, small-angle neutron scattering, and cryo-transmission electron microscopy were combined to investigate the structure and properties of mixed wormlike micelles (WLMs) of zwitterionic (oleylamidopropyl dimethyl betaine) and anionic (sodium dodecylsulfate) surfactants. This system demonstrates the formation of giant linear long-lived WLMs, which even at extremely low surfactant concentration reach a sufficient length to entangle with each other and form a three-dimensional temporally persistent network. Stability of these micelles can be due to electrostatic attraction between the headgroups of the anionic and zwitterionic surfactants and favorable volume/length hydrophobic ratio in the surfactant mixture. Heating of these systems leads to the transition of temporally persistent network with predominantly elastic properties into transient network exhibiting viscoelasticity, which is due to the shortening of long-lived WLMs. At increasing surfactant concentration, the long-lived linear micelles transform into fast-breaking branched micelles, which is due to the screening of electrostatic interactions by salt released from the dissociated surfactant molecules. The transition results in the drop of viscosity and approaches the system to the behavior of Maxwell fluid with a single relaxation time. The observed structural transitions strongly affecting the rheological properties can be exploited in various applications of zwitterionic surfactants.

A portable digital optical kanamycin sensor developed by surface-anchored liquid crystal droplets

There is an increase in demand to develop simple, convenient, and low-cost approaches for rapid and label-free detection of antibiotics. Herein, we propose a new principle for the detection of kanamycin using the surface-anchored liquid crystal (LC) droplets. The optical images of the LC droplets uniformly change from four-clover, uniformly dark, and dark cross appearance gradually with the increase of surfactant concentration. The detection of kanamycin is fulfilled with the aid of a cationic surfactant cetyltrimethylammonium bromide (CTAB) and a kanamycin aptamer. The LC droplets show uniformly dark appearance and four-clover appearance in the presence of the aqueous solutions of CTAB and CTAB/aptamer complex, respectively. However, the specific binding of kanamycin to its aptamer can release the CTAB, which induces the uniformly dark appearance of the LC droplets. A portable device is built to measure the optical luminance of the LC droplets. This system can detect kanamycin with a concentration below 0.1 ng/mL (~0.17 nM) and also allows the detection of kanamycin in real samples such as milk and honey. Therefore, it is very promising in the development of new types of LC-based sensors by the surface-anchored LC droplets assisted with a portable optical device.

Interactions of Surfactants with Biomimetic Membranes. 1. Ionic Surfactants

AbstractWhen impregnated with esters of fatty acids, nitrocellulose filters can be used as a biomimetic membrane. They are easy to make, cheap, and may be used not only as an imitation of biological membranes but also as a sensor to characterize surfactant interactions with dirty fabric. These impregnated filters when fixed in a thermostatically controlled chamber separated into two compartments that contain stirred aqueous solutions by the filter, may be considered as a simple model of a laundry machine. The results revealed that the addition of ionic surfactants into one of the solutions led to the formation of transmembrane electrical potential that is proportional to the logarithm of surfactant concentration. Thus, our biomimetic membranes can be used as electrochemical sensors to detect and measure surfactant concentration. When concentration is near the critical micelle concentration (CMC), a new phenomenon was observed, i.e., spontaneous oscillations of both transmembrane potential and transmembrane current, which mimics the opening and closing of aqueous channels in biological membranes. A further increase of surfactant concentration les to a sharp 100‐fold decrease of transmembrane electrical resistance and the disappearance of any transmembrane voltage. This effect, explained by the washing out of fatty acids from the pores, may be used for screening and development of new detergents.

Strong Modulation of Short Wind Waves and Ka-Band Radar Return Due to Internal Waves in the Presence of Surface Films. Theory and Experiment

Strong variability of Ka-band radar backscattering from short wind waves on the surface of water covered with surfactant films in the presence of internal waves (IW) was studied in wave tank experiments. It has been demonstrated that modulation of Ka-band radar return due to IW strongly depends on the relationship between the phase velocity of IW and the velocity of drifting surfactant films. An effect of the strong increase in surfactant concentration was revealed in convergent zones, associated with IW orbital velocities in the presence of a “resonance” surface steady current, the velocity of which was close to the IW phase velocity. A phenomenological model of suppression and modulations in the spectrum of small-scale wind waves due to films and IW was elaborated. It has been shown that backscatter modulation could not be explained by the modulation of free (linear) millimeter-scale Bragg waves, but was associated with the modulation of bound (parasitic) capillary ripples generated by longer, cm–dm-scale waves—a “cascade” modulation mechanism. Theoretical analysis based on the developed model was found to be consistent with experiments. Field observations which qualitatively illustrated the effect of strong modulation of Ka-band radar backscatter due to IW in the presence of resonance drift of surfactant films are presented.

Abstract P-38: Tunable Soft Networks of Wormlike Micelles and Clay Particles

Background: Over the past few decades, there has been a great deal of interest in the aqueous self-assembly of surfactant molecules into giant wormlike micelles (WLMs). These cylindrical aggregates undergo reversible breakdown processes and in favorable cases can grow up to few tens of micrometers that is comparable with the length of high molecular weight polymer. The viscoelastic properties of WLMs can be easily modified by different additives like salts or polymers. A new emerging research area consists of tuning the WLM solution properties by inorganic nanoparticles. It suggests, in particular, the use of networks of entangled WLMs as a matrix for producing soft nanocomposites with different kinds of embedded nanoparticles that are promising for controlled release, template synthesis, and oilfield applications. These materials can combine adaptive rheological properties of the WLM matrix and the functionality of nanofiller. Methods: Rheometry and cryo-transmission electron microscopy were combined to investigate the structure and properties of mixed WLMs of zwitterionic oleylamidopropyl dimethyl betaine and anionic sodium dodecyl sulfate surfactants and platelike particles of bentonite clay. Results: This system demonstrates the formation of giant linear long-lived WLMs, which even at extremely low surfactant concentrations reach a sufficient length to entangle with each other and form a temporally persistent network. The stability of these micelles can be due to electrostatic attraction between the headgroups of the anionic and zwitterionic surfactants and favorable volume/length hydrophobic ratio in the surfactant mixture. At increasing surfactant concentration, the long-lived linear micelles transform into fast-breaking branched micelles. Stable viscoelastic suspensions of clay particles in semi-dilute solutions of WLM were elaborated. They represent a novel type of soft nanocomposite with the tunable matrix. Structural studies revealed that the clay is dispersed in a dense network of entangled WLM in the form of 100-nm tactoids. Rheological investigations demonstrated that clay particles can induce an increase of viscosity and relaxation time by up to one order of magnitude. The effect of the clay becomes more pronounced with increasing content of anionic surfactant, when the micelles become branched. This behavior was explained by the stabilization of micelle-nanoclay junction points due to the screening of the repulsion between positively charged fragments of zwitterionic head groups by added anionic surfactant. Conclusion: The pronounced effect of nanoparticles on the viscoelasticity of the network formed by branched WLMs was observed for the first time. The nanoparticles-WLM junctions were confirmed by cryo-TEM data. The elaborated systems are of interest for many industrial applications.

Investigation on Hydrate Growth at the Oil-Water Interface: In the Presence of Wax and Surfactant.

Natural gas hydrates can readily form in deep-water-oil production processes and pose a great threat to subsea pipeline flow assurance. The usage of surfactants and hydrate antiagglomerants is a common strategy to prevent hydrate hazards. In water/wax-containing oil systems, hydrate coexisting with wax could lead to more complex and risky transportation conditions. Moreover, the effectiveness of surfactants and hydrate antiagglomerants in the presence of wax should be further evaluated. In this work, for the purpose of investigating how wax and surfactants could affect hydrate growth at the oil-water interface, a series of microexperiments was conducted in an atmospheric visual cell where the nucleation and growth of hydrates took place on a water droplet surrounded by wax-containing oils. On the basis of the experimental phenomena observed using a microscope, the formation of a hydrate shell by lateral growth, the collapse of a water droplet after hydrate initial formation, and the formation of hollow-conical hydrate crystals were identified. These experimental phenomena were closely related to the concentration of wax and surfactant used in each case. In addition, it was shown that the effectiveness of the surfactant could be weakened by wax molecules. Moreover, there existed a critical wax content above which the effectiveness of the surfactant was greatly reduced and the critical wax content gradually increased with increasing surfactant concentration. This work could provide guidance for hydrate management in wax-containing systems.

Interaction of Bis-Guanidinium Acetates Surfactants with Bovine Serum Albumin Evaluated by Spectroscopy

Abstract The interactions between cocopropane bis-guanidinium acetates, tallowpropane bis-guanidinium acetates with bovine serum albumin (BSA) in an aqueous solution were studied by fluorescence and circular dichroic spectroscopy measurements. The aim of the study was to elucidate the influence of the hydrophilic group and the length of the hydrophobic chain of these surfactants on the mechanism of binding to BSA. The results revealed that for both surfactants, at low concentrations, the Stern–Volmer plots had an upward curvature and at high concentrations, the quenching efficiency was decreased with increase in surfactant concentration. Different thermodynamics parameters demonstrated the existence of hydrogen bond and van der Waals force which acting as binding forces. Static quenching was observed among the protein and surfactant. The conformation of BSA was changed at higher surfactant concentrations as shown by synchronous fluorescence and CD spectroscopy. This work reveals the mechanism and binding characteristics between guanidine surfactants and protein, and provided the basis for further applications of surfactants.

Cobalt removal from an industrial effluent by foam fractionation

In this study, the removal of cobalt from an effluent was investigated probably for the first time by foam fractionation. Foam fractionation is considered as a green method because of its friendly nature, high removal efficiency, costs effectiveness and non-hazardous nature. Sodium dodecyl sulfate (SDS) was used as an anionic surface-active agent and the effect of gas flow rate, the initial concentrations of surfactant and cobalt and pH on the cobalt removal efficiency was investigated. The results showed that by increasing surfactant concentration and gas flow rate, the cobalt removal efficiency would be improved however, the cobalt concentration in foamate would decrease at high gas flow rates. High gas flow rates generally produce dilute foamate. Drainage of the interstitial bulk fluid that is entrapped between the foam bubbles has a key importance in the normal performance of the foam fractionation operation. Experiments showed that the well-drained foams are low in volume and high in Co2+ leading to an easier separation of their ingredients that usually follows. The efficiency reached the highest when cobalt feed concentration was about 1 mg/L, but dropped gradually in higher concentrations. By increasing pH to around 5, high removal efficiency was achieved and then decreased again. The optimum conditions for high cobalt removal efficiency were obtained when SDS concentration was about 100 mg/L and the initial cobalt concentration was below and close to 1 mg/L. The results of experiments revealed that the amount of cobalt removed per unit weight of SDS was higher for low [SDS]/[Co2+] ratios. They also showed that the air–liquid interface coverage by surface excess solute ions would not be more that 5% of the total area. Under optimum conditions for cobalt removal pH value and gas flow rate were found to be around 5 and 9 L/h, respectively. Under these conditions the removal efficiency was shown to be 99.4%.

Novel epigallocatechin gallate-based polyether surfactants: Synthesis, characterization and demulsification properties

Natural polyphenols such as tannins, procyanidins, and cardanol are widely used in the field of surface chemistry. To further explore the application of the other natural polyphenols, epigallocatechin gallate (EGCG) derived from green tea was employed. EGCG is an ideal choice to achieve a hyperbranched surfactant. A precursor (EGA) was first obtained by the reaction among the EGCG, formaldehyde, and tetraethylenepentamine (TEPA). EGA surfactants were synthesized in the high-pressure kettle by anionic polymerization with EGA, propylene oxide (PO) and ethylene oxide (EO). The good consistency between the designed PO/EO ratios of EGA surfactants and the theoretical values were proved by 1H NMR spectra. The increase of micelle size with the increase of surfactant concentration and NaCl concentration was observed both by dynamic light scattering and TEM. Result shows EGA surfactants with higher absolute value of ∆G°ads and high interfacial activity have potential demulsification applications. As a result, toward aging oil emulsions of the South China Sea Oilfield, the surfactants exhibited excellent demulsification performance. The dehydration ratio reached 94.3% at a low concentration of 100 mgL−1 for 100 min at 70°C, while the commercial demulsifier SP169 only reached 86.9%. This emulsion could be dehydrated completely at even higher temperature at 80°C as well as higher dosage in 150 mgL−1. Meanwhile, the demulsification ratios of crude oil emulsions and aging oil emulsions produced from Bohai Oilfield reached 94.0% and 95.0%, respectively. Coming from the waste oil after demulsification, aging oil emulsions have more additives than crude oil emulsions, therefore the former is more stable. In addition to the above high interfacial activity, this excellent demulsification performance may result from the assistance of polyphenol structure and multiple branches of EGA surfactants. The demulsification of three above emulsions demonstrated that although there exist great differences in properties of emulsions, EGA surfactants exhibit the universality of efficient demulsification.

An Advanced Material with Synergistic Viscoelasticity Enhancement of Hydrophobically Associated Water‐Soluble Polymer and Surfactant

In order to prepare materials with controllable properties, changeable microstructure, and high viscoelasticity solution with low polymer and surfactant concentration, a composite is constituted by adding surfactant (sodium dodecyl sulfate, SDS) to hydrophobically associated water-soluble polymer (abbreviated as PAAC) solution. The viscoelasticity, aggregate microstructure, and interaction mechanism of the composite are investigated by rheometery, Cryo-transmission electron microscopy (Cryo-TEM), and fluorescence spectrum. The results show that when the mass ratio of polymer to surfactant is 15:1, the viscosity of the composite reaches the maximum. The viscosity of the composite system increases hundredfold. The viscosity plateau under dynamic shear is generated. The composite has the properties of high viscoelasticity, strong shear thinning behavior, and good salt tolerance, and temperature resistance. The maximum viscosity of the composite is shown at the salinity of 20000mg L-1 . In addition, there is no phase separation in the composite with the increase of polymer and surfactant concentration, which indicates the good stability of the system. It is proposed a method to obtain a high viscoelasticity solution by adding surfactants without wormlike micelles to a hydrophobically associated water-soluble polymer solution.

Synergistic Effect of Binary Surfactant Mixtures in Two-Phase and Three-Phase Systems.

Cationic alkyltrimethylammonium bromides (CnTAB, with n = 8, 12, 16, 18) and their mixtures with n-octanol as a nonionic surfactant were chosen as a model system to study the synergistic effect on foamability (two-phase system) and floatability (three-phase system) of quartz in the presence of binary mixtures of ionic/nonionic surfactants. The foam height of one-component solutions and binary mixtures and floatability of quartz particles were characterized as a function of the surfactant concentration and the number of carbons (n) in the alkyl chain of CnTAB. The experimental results of foamability and floatability measurements in one-component and mixed solutions revealed the synergistic effect, causing a significant enhancement in the foam height and recovery of quartz. In the presence of n-octanol, the height of foam increased remarkably for all CnTAB solutions studied, and this effect, whose magnitude depended on the CnTAB hydrophobic tail length, could not be justified by a simple increase in total surfactant concentration. A similar picture was obtained in the case of flotation response. The mechanism of synergistic effect observed in mixed CnTAB/n-octanol solutions was proposed. The discussion was supported by molecular dynamics simulations, and the probable mechanism responsible for synergism was discussed. In addition, an analysis allowing accurate determination of the concentration regimes, where the synergistic effect can be expected, was given. It was shown that for the two-phase system, the n-octanol molecule preadsorption at the liquid/gas interface causes an increase in CnTAB adsorption coverage over the level expected from its equilibrium value in the one-component solution. In the case of the three-phase system, the synergistic effect was related to the ionic surfactants serving as an anchor layer for n-octanol, which, in water/n-octanol solution (one-component system), do not adsorb on the surface of quartz.

Effect of anionic and non-anionic surfactants on the adsorption density

Surfactant adsorption is one of the crucial issues in surfactant flooding to enhance the oil recovery factor. In this paper, we investigated the profound impact of two different surfactants on the carbonate rocks adsorption density in different temperatures. According to the results of this experiment, carbonate rocks adsorption density increased with the increase of surfactant concentrations. Higher surfactants’ concentration, adsorption density had reached a plateau after 7 hours. Furthermore, temperature increase has caused to reduce the adsorption density for all surfactant concentration. The maximum adsorption density is about 50 mg/g at 20 Besides, polyacrylamide addition would decrease the adsorption density.