Polymer-surfactant Systems Research Articles

Study on Surfactant-Polymer Flooding after Polymer Flooding in High-Permeability Heterogeneous Offshore Oilfields: A Case Study of Bohai S Oilfield.

Polymer flooding is an effective development technology to enhance oil recovery, and it has been widely used all over the world. However, after long-term polymer flooding, a large number of oilfields have experienced a sharp decline in reservoir development efficiency. High water cut wells, serious dispersion of residual oil distribution and complex reservoir conditions all bring great challenges to enhance oil recovery. In this study, the method of enhancing oil recovery after polymer flooding was studied by taking the S Oilfield as an example. A surfactant-polymer system suitable for high-permeability heterogeneous oilfields was developed, comprising biogenic surfactants and polymers. Microscopic displacement experiments were conducted using cast thin sections from the S Oilfield, and nuclear magnetic resonance was employed for core displacement experiments. Numerical simulation experiments were also conducted on the S Oilfield. The results show that the enhanced oil recovery mechanism of the surfactant-polymer system is to adjust the flow direction, expand the swept volume, emulsify crude oil and reduce interfacial tension. Surfactant-polymer flooding proves to be effective in improving recovery efficiency, significantly reducing the time of flooding and further enhancing the strong swept area. The nuclear magnetic resonance results indicate a high amplitude of passive utilization of residual oil during the surfactant-polymer flooding stage, highlighting the enormous potential for an increased recovery ratio. Surfactant-polymer flooding emerges as a more suitable technique to enhance oil recovery in the post polymer-flooding stage in high-permeability heterogeneous oilfields.

A study on the emulsification ability and oil displacement efficiency of polymeric surfactant in porous media

In order to comprehensively comprehend the distinctions in solution properties, emulsification characteristics, and oil displacement efficiency between polymeric surfactant(DG-1) and traditional polymers or surfactants, a comparative analysis was initially conducted on the microstructure, main functional group types, and macroscopic properties. Subsequently, core displacement experiments were employed to elucidate the emulsification capability, emulsion stability, and oil displacement properties of polymeric surfactants. The microscopic displacement experiment was ultimately conducted to investigate the residual oil displacement process in the core following polymer displacement by DG-1, thereby elucidating the underlying mechanisms of microscopic oil displacement by DG-1. The results indicate DG-1 has a molecular structure with a regional network aggregation state as a whole, and a multi-layer aggregation and overlapping structure in space. DG-1exhibits higher viscosity and lower interfacial tension due to the larger molecular coil dimension compared to the equivalent concentration of polymers. The emulsification ability of DG-1 is robust, with emulsion stability positively correlated to oil-polymer ratio and concentration while negatively correlated to migration distance. Core displacement experiments results indicate the polymer-surfactant system (SP) and DG-1 exhibited comparable oil displacement effects, with oil recovery of 54.5 % and 52.4 %, respectively, both surpassing the recovery achieved by the polymer alone (46.9 %). In heterogeneous reservoirs, SP acts as the dominant displacer in regions with moderate and high permeability, whereas DG-1 assumes dominance in regions with moderate and low permeability. The microscopic displacement experiments revealed that DG-1 activated the clustered residual oil as the predominant type of residual oil in porous media, followed by columnar and block residual oil, with film residual oil exhibiting the least activation. Primary mechanisms for oil displacement include extended sweeping volume, shear and carrying effects on the residual oil, and eddy displacement of the residual oil by the emulsion.

Towards natural care products: Structural and deposition studies of bio-based polymer and surfactant mixtures

Oppositely charged polymer-surfactant systems are expected to interact with formation of coacervate complexes near composition of charge-neutrality. Such behaviour is widely used in formulated products (e.g. household and personal care), where the co-deposition of coacervates and active ingredients on various surfaces is triggered by dilution. A transition towards the use of more sustainable ingredients is currently ongoing as a response to the need of more environmentally conscious choices in production, albeit slowed down by the often more complex and not fully understood bulk and interfacial behaviour of new ingredients. In this work, mixtures of a medium-chain fatty acid (sodium decanoate) and two grades of bio-based cationic modified inulin were studied. The phase behaviour was determined in a wide composition matrix. The formation of coacervate complexes was observed for the mixture with the higher charge density polymer at a surfactant concentration of 1–3 wt%, close to the surfactant critical micellar concentration in pure water. Such behaviour was confirmed by DLS and SAXS data, suggesting surfactant-polymer complexation in a concentrated phase of packed micelles with a micelle-to-micelle distance of ∼4.5 nm. In situ ellipsometry and neutron reflectometry experiments were conducted to study the effect on surface deposition when diluting. The ellipsometry showed an adsorbed mass of ∼1.3–1.9 mg/m2, consistent with the deposition of a coacervate layer, and considerably higher than the neat, adsorbed polymer layer of ∼0.3 mg/m2. In the case of the neutron reflectometry experiments, dilution was performed before contact with the surface (pre-mixing), and no adsorption of coacervates was observed, but rather the adsorption of a polymer layer (0.49–0.85 mg/m2). The different results obtained with the different techniques highlight the kinetic nature of bulk coacervate formation and deposition, and the competition between these two phenomena. Maximal deposition can be achieved if one can control this time window either by tuning the composition of the system or the experimental set-up, to mimic the conditions of a specific application.

Synergistic collaborations between surfactant and polymer for in-situ emulsification and mobility control to enhance heavy oil recovery

Surfactant-polymer (SP) combined systems is an effective nonthermal method to enhance the heavy oil recovery, through in-situ emulsification and mobility control mechanisms. In this study, a novel SP system was developed using 0.2 wt% anionic surfactant (alkyl naphthol polyoxyethylene ether sulfonate, ANES) and 0.1 wt% polymer (partially hydrolyzed polyacrylamide, HPAM). The SP system had viscosity reduction rate of ∼ 98 %, viscosity ratio of oil to displaced water (μo/μd) of ∼ 3.95 and IFT of ∼ 0.29 mN/m, beneficial for decreasing the mobility ratio of water to heavy oil. Then, the applied performances including emulsion morphologies and stability, wettability alteration ability were systematically characterized. The results showed that the freshly O/W emulsions formed by SP system displayed uniform droplet size distribution, as well as high stability with tight interfacial film. In addition, the SP system exhibited excellent wettability alteration property with low contact angle of 18.3°. The synergistic collaboration mechanisms of surfactant and polymer include heavy oil–water interfacial tension reduction, in-situ emulsification, oil-viscosity reduction and water-viscosity increase. Finally, the static oil washing and dynamic sand-pack flooding experiments showed that the SP system exhibited high oil washing efficiency (62.89 %) and enhanced oil recovery efficiency (56.9 %) with improving the mobility controllability after the primary water-flooding process. This study indicated that the synergistic collaborations between surfactant and polymer had great potential to enhance the heavy oil recovery.

Pressure Changes Across a Membrane Formed by Coacervation of Oppositely Charged Polymer-Surfactant Systems.

We investigate the mass transfer and membrane growth processes during capsule formation by the interaction of the biopolymer xanthan gum with CnTAB surfactants. When a drop of xanthan gum polymer solution is added to the surfactant solution, a membrane is formed by coacervation. It encapsulates the polymer drop in the surfactant solution. The underlying mechanisms and dynamic processes during capsule formation are not yet understood in detail. Therefore, we characterized the polymer-surfactant complex formation during coacervation by measuring the surface tension and surface elasticity at the solution-air interface for different surfactant chain lengths and concentrations. The adsorption behavior of the mixed polymer-surfactant system at the solution-air interface supports the understanding of observed trends during the capsule formation. We further measured the change in capsule pressure over time and simultaneously imaged the membrane growth via confocal microscopy. The cross-linking and shrinkage during the membrane formation by coacervation leads to an increasing tensile stress in the elastic membrane, resulting in a rapid pressure rise. Afterward, the pressure gradually decreases and the capsule shrinks as water diffuses out. This is not only due to the initial capsule overpressure but also due to osmosis caused by the higher ionic strength of the surfactant solution outside the capsule compared to the polymer solution inside the capsule. The influence of polymer concentration and surfactant type and concentration on the pressure changes and the membrane structure are studied in this work, providing detailed insights into the dynamic membrane formation process by coacervation. This knowledge can be used to produce capsules with tailored membrane properties and to develop a suitable encapsulation protocol in technological applications. The obtained insights into the mass transfer of water across the capsule membrane are important for future usage in separation techniques and the food industry and allow us to better predict the capsule time stability.

Heavy oil removal using modified polyacrylamide and SDS

Composite systems of surfactants have been extensively applied in the recovery and removal of heavy oil. In this work, the characteristics and mechanisms of heavy oil removal in surfactant-polymer systems (SP) were investigated. The effects of the main factors, including the oil-to-water ratio, washing temperature, washing time, and shear rate, on the oil washing rate (OWR) were analyzed through the response surface methodology (RSM). The results demonstrated the ratio of oil to water had the most significant impact on the OWR compared to other factors. Based on the experimental data and the analysis of variances, a high-precision model was established, and the predicted OWR value was 42.0 % at the formation temperature (50 °C). In addition, the adsorption process of the SP molecules onto quartz silica was well represented by the pseudo-second-order kinetic model and the Freundlich isotherm. This indicates that the SP system has the characteristics of multilayer rebinding and heterogeneous adsorption. On the other hand, the adsorption thermodynamics identified that the adsorption was endothermic and unspontaneous. The dynamic experiments showed that the removal of heavy oil was clean and efficient without secondary adsorption and contamination on the solid surface. Furthermore, the oil removal of the SP system was determined by the mechanism of wettability alteration, utilizing the adsorption of SP molecules onto the solid surface to displace the adsorbed heavy oil molecules. The findings enhance the understanding of heavy oil removal by the surfactant-polymer composite system, which is frequently overlooked in conventional methodologies.

In-situ emulsification in low-tension surfactant/polymer systems: Impacts on enhanced oil recovery

The flow of two immiscible liquids in porous media can lead to fluid mixing, resulting in emulsions—where one phase is dispersed as droplets in the other. In reservoir rocks, natural surfactants and polar molecules, like asphaltenes, can promote oil–water emulsion formation. During chemically enhanced oil recovery processes (CEOR) such as surfactant, alkali, or surfactant-alkali flooding, in-situ emulsification is often seen as key to enhancing frontal stability and facilitating the piston-like displacement of oil by water. However, this work reports a minimal effect of in-situ emulsification on oil production during surfactant-polymer (SP) flooding. Experimental studies show this by injecting prepared emulsions into a multi pressure-tap core holder and examining emulsion formation in one reservoir core before moving it into a second core for oil displacement. This helps us understand the specific role of emulsions in oil mobilization. Factors like surfactant concentration, interfacial tension, and the timing of introducing the surfactant-polymer solution do influence the intensity of in-situ emulsification. Yet, the incremental oil recoveries show no significant differences. Through similar experiments, it is observed that ultra-low interfacial tension (IFT) in our surfactant-polymer system is the primary mechanism for oil mobilization. The slight increase in pressures suggests that in-situ emulsification has a limited role in increasing flow resistance during the ultra-low IFT SP flood process, potentially not improving the swept volume. This research can guide the development of systematic approaches to analyze the effects of in-situ emulsification on oil mobilization and evaluate chemical flooding processes.

Comparing polymer-surfactant complexes to polyelectrolytes

HypothesisUnderstanding the complex interactions between polymers and surfactants is required to optimise commercially relevant systems such as paint, toothpaste and detergent. Neutral polymers complex with surfactants, forming ‘pearl necklace’ structures that are often conceptualised as pseudo-polyelectrolytes. Here we pose two questions to test the limits of this analogy: Firstly, in the presence of salt, do these polymer-surfactant systems behave like polyelectrolytes? Secondly, do polymer-surfactant complexes resist geometric confinement like polyelectrolytes? ExperimentsWe test the limits of the pseudo-polyelectrolyte analogy through studying a poly(N-isopropylacrylamide) (PNIPAM) brush in the presence of sodium dodecylsulfate (SDS). Brushes are ideal for interrogating pseudo-polyelectrolytes, as neutral and polyelectrolyte brushes exhibit distinct and well understood behaviours. Spectroscopic ellipsometry, quartz crystal microbalance with dissipation monitoring (QCM-D), and neutron reflectometry (NR) were used to monitor the behaviour and structure of the PNIPAM-SDS system as a function of NaCl concentration. The ability of the PNIPAM-SDS complex to resist geometric confinement was probed with NR. FindingsAt a fixed SDS concentration below the zero-salt CMC, increasing NaCl concentration <100 mM promoted brush swelling due to an increase in osmotic pressure, not dissimilar to a weak polyelectrolyte. At these salt concentrations, the swelling of the brush could be described by a single parameter: the effective CMC. However, at high NaCl concentrations (e.g., 500 mM) no brush collapse was observed at all (non-zero) concentrations of SDS studied, contrary to what is seen for many polyelectrolytes. Study of the polymer-surfactant system under confinement revealed that the physical volume of surfactant dominates the structure of the strongly confined system, which further differentiates it from the polyelectrolyte case.

Designing effective enhanced oil recovery fluid: Combination of graphene oxide, D118 SuperPusher, and Chuback surfactant

Enhanced oil recovery (EOR) is one of the most essential branches of petroleum engineering and aims to maximize oil extraction from reservoirs. This research focuses on the utilization of graphene oxide (GO) in combination with a D118 SuperPusher compound and a natural surfactant (Chuback) to enhance oil recovery. The objective is to optimize the efficiency of the EOR process through a multi-component approach. The application of Chuback leads to a substantial decrease in interfacial tension (IFT), particularly in carbonate rock formations. This is attributed to the unique characteristics of carbonate rocks, which exhibit greater susceptibility to wettability alterations. Moreover, GO nanoparticles (NPs) were synthesized, then characterized and incorporated into the surfactant-polymer system, creating surfactant-polymer-nanoparticle (SPN) fluids. The selection of optimum fluid formulations for the EOR process is facilitated through the utilization of Design Expert, a statistical software tool. Factors such as surfactant concentration, polymer concentration, NPs concentration, and two types of salt concentrations are specifically chosen as variables that can influence the fluid's performance during the flooding step. Parameters including IFT, contact angle (CA) (which affects wetting behavior), and shear viscosity (which impacts fluid flow) are considered responses. The efficacy of the suggested fluid formulation for EOR is validated through core flooding investigations. Core flooding investigations validated the efficacy of the suggested fluid for EOR, with recovery factors of up to 30% and 56% in sandstone and carbonate core samples, respectively. These findings underscore the potential of the proposed approach to significantly enhance oil recovery from both sandstone and carbonate reservoirs.

Adaptability and enhanced oil recovery performance of surfactant–polymer flooding in inverted seven-spot well pattern

As one of the leading technologies for chemical enhanced oil recovery (cEOR), surfactant–polymer (SP) flooding technology has long attracted the interest of petroleum scientists and engineers. However, most of its application scenarios are based on the five-spot well pattern. The EOR potential in an inverted seven-spot well pattern is seldom ever recorded. The applicability of the SP system in the inverted seven-spot well pattern was examined based on the physical characteristics of Karamay Oilfield in China. The numerical simulation and the one-dimensional core flooding experiment were used to compare the sweep intensities and EOR abilities of the two well patterns. The migration law and the EOR ability of the SP system were assessed by a specially made one-third inverted seven-spot configuration. The main controlling factors and compatibility charts of SP flooding development in the inverted seven-spot well pattern were obtained. Results show that 61% of the region is represented by a weak swept state in the inverted seven-spot well pattern. The effective swept area is greatly increased by appropriately raising the viscosity and slug size of the SP system. Compared to constant viscosity injection, step-down viscosity injection further increases the sweep range and oil recovery. The inverted seven-spot well pattern has a greater swept area of the SP system than the five-spot one, but a weaker strength. Polymer concentration is the most effective factor of SP flooding in the inverted seven-spot well pattern, followed by oil viscosity and surfactant concentration. The study can broaden the application of the SP system in the inverted seven-spot well pattern.

Study on Oil Recovery Mechanism of Polymer-Surfactant Flooding Using X-ray Microtomography and Integral Geometry.

Understanding pore-scale morphology and distribution of remaining oil in pore space are of great importance to carry out in-depth tapping of oil potential. Taking two water-wet cores from a typical clastic reservoir in China as an example, X-ray CT imaging is conducted at different experimental stages of water flooding and polymer-surfactant (P-S) flooding by using a high-resolution X-ray microtomography. Based on X-ray micro-CT image processing, 3D visualization of rock microstructure and fluid distribution at the pore scale is achieved. The integral geometry newly developed is further introduced to characterize pore-scale morphology and distribution of remaining oil in pore space. The underlying mechanism of oil recovery by P-S flooding is further explored. The results show that the average diameter of oil droplets gradually decreases, and the topological connectivity becomes worse after water flooding and P-S flooding. Due to the synergistic effect of “1 + 1 > 2” between the strong sweep efficiency of surfactant and the enlarged swept volume of the polymer, oil droplets with a diameter larger than 124.58 μm can be gradually stripped out by the polymer-surfactant system, causing a more scattered distribution of oil droplets in pore spaces of the cores. The network-like oil clusters are still dominant when water flooding is continued to 98% of water cut, but the dominant pore-scale oil morphology has evolved from network-like to porous-type and isolated-type after P-S flooding, which can provide strong support for further oil recovery in the later stage of chemical flooding.

Fabrication of surfactant-biopolymer combined system with dual viscosity reduction and mobility controllability for heavy oil reservoirs

Surfactant-polymer (SP) combined systems have been proven to be efficient for enhancing heavy oil recovery through in-situ emulsification and water thickening mechanisms due to their dual viscosity reduction and mobility controllability. In this study, 0.1 wt% anionic surfactant (fatty alcohol polyoxyethylene ether sulfate, SC) and 0.05 wt% biopolymer (xanthan gum, XG) were combined to develop a novel SP system (SC-XG). The emulsification properties including stability, droplet morphology and size distribution, as well as oil–water interfacial tension (IFT), rheology were systematically investigated. The results showed that the addition of XG into SC systems could obviously decrease the viscosity ratio of oil to displaced water (μo/μd) to 1.42 and simultaneously maintain the high viscosity reduction rate at 94.03 %, which is beneficial for decreasing the mobility ratio of water to oil (M). Besides, the emulsion prepared by SC-XG displayed stronger stability and smaller droplet size compared to those of SC after aging 2 h. Although the addition of XG into SC system could slightly increase the oil–water IFT, the viscosity and viscoelasticity were significantly strengthened and displayed main contributions to the enhancement of emulsion stability. Finally, the sand-pack flooding experiments showed that the optimum SC-XG system could enhance the heavy oil recovery by 20.20 % after brine flooding process, which exhibited dual viscosity reduction and mobility controllability. This study demonstrates the facile design and potential applications of SP system for heavy oil reservoirs.

Experimental studies of surfactant-polymer flooding: An application case investigation

A great deal of oil field is currently produced using water flooding and the water cut has reached a high level, which requires enhanced oil recovery (EOR) techniques to improve the recovery. Surfactant-polymer (SP) flooding is the combination of surfactant flooding and polymer flooding. The polymer is added to increase the viscosity and viscoelasticity of the fluid while the surfactant is included to decrease the oil–water interfacial tension and change the wettability. Although the mechanism of SP flooding has been deeply investigated, the application of SP flooding on a specific oil field requires the selection of optimal SP system. Therefore, for the first time, we performed a series of experiments to determine the optimal SP system for high water-cut oil field. In the injection capability experiment, we observe that the SP system is injected into the core with less resistance compared with single polymer solution. In the flooding experiment, regardless of the polymer types, the improvement of recovery becomes significant when the injected PVs increases. SP flooding shows the higher improvement of recovery compared with single polymer flooding or surfactant flooding. Based on the performance of recovery improvement, we recommend the optimal SP system for the studied case is the combination of DQ-TSRP01 polymer and surfactant. The optimal injection parameters of this SP system are 1500 mg/L polymer concentration, 0.3 injection PV and the injection timing of 96% water cut. The finding of this study can help for better understanding of the application of SP flooding in high water-cut oil field production.

Surfactant–polymer binary oil-displacement agents suitable for multiple oilfield blocks

In oil-displacement processes, a compound surfactant system is used to reduce the crude oil–water interfacial tension (IFT) via the synergistic effect of multiple surfactants. To the best of our knowledge, however, since there is no systematic quantitative comparison tool for the intermolecular effects of surfactants, the synergistic mechanisms of surfactant systems have not been analyzed in depth. This paper proposes the use of intermolecular scission energy as a quantitative tool to analyze the synergistic mechanism of surfactants, mitigating the aforementioned issues. As a case study, this paper focuses on the Y-1, K-1, and K-2 blocks of Shengli Oilfield, China. Based on the intermolecular scission energies of the crude oil IFT-reducing agents of each block, along with the fact that they have the same composition, the co-surfactant amide betaine was added to a conventional alkanolamide–hydroxysultaine system to form a common surfactant system suitable for use in all three blocks. This new system achieved ultra-low IFTs—that is, ∼10−3 mN/m—for all three oils at a concentration of only 0.05%. The surfactant system can effectively reduce the oil–water IFT for 125 days under 90 °C formation conditions, with good thermal stability. After flowing in the formation for 30 days, the concentration of the system is still maintained at about 95%, and it is not easily adsorbed. In the visualization of the oil displacement test, the total oil recovery of a surfactant–polymer system (SP system)—composed of a surfactant system and a polymer—was found to be over 62%, an increase of more than 20%.

Classification methods of conglomerate reservoirs based on the adsorption and retention law of surfactant-polymer binary systems

Factors such as clay minerals and micropore structure can lead to the adsorption and retention of chemical agents when the components of surfactant-polymer systems enter porous media. This study aims to clarify the influence of adsorption and retention of surfactant-polymer components on reservoir permeability and oil displacement efficiency and then classify the reservoirs into types. The natural cores of conglomerate reservoirs from the Badaowan Formation in the 7th block are selected as research objects to reveal the adsorption law of surfactant-polymer components on different minerals and different micro pores through the dynamic oil displacement method based on physical model and the N element calibration method. Experimental results show that the adsorption capacity of clay minerals for surfactant-polymer components is significantly higher than that of carbonate and skeleton minerals, and different clay minerals differ in adsorption capacity for surfactant-polymer components depending on their cation exchange capacity and end surface adsorption activity. In addition, the adsorption and retention capacities of reservoirs for surfactant-polymer components are closely related to the type and content of clay minerals. The combination type of clay minerals controls the adsorption activity of surfactant-polymer components, and the values of polymer and the surfactant are quantitatively calculated to be 11.3 and 21.4 mg/g, respectively. The adsorption strength of surfactant-polymer components is controlled by the content of clay minerals. With increasing clay content, the adsorption strength of the polymer ranges from 0.5 to 2.5 mg/cm 3 , and that of the surfactant ranges from 1.0 to 4.5 mg/cm 3 . On this basis, the “N element calibration method” is used to determine the occurrence state and content of chemical agents in micropores for different permeability samples after surfactant-polymer binary flooding. Research results show that the polymer and surfactant components mainly have two types of occurrence form in micropores, including the complex pores accumulated by clay minerals and the intersections of small pores and throats. With decreasing reservoir permeability, the number and content of detected N element gradually increase, indicating an increase in the adsorption and retention of polymer and surfactant, and the influence on the reservoir seepage capacity also increases. Finally, the conglomerate reservoirs in the Badaowan Formation from the 7th block are divided into four types after considering the influence of clay minerals and micropore structure on the adsorption and retention of surfactant-polymer components, and the reasonable classification of reservoir types can effectively enhance the oil recovery of surfactant-polymer binary flooding. • The adsorption law of SP binary components on different minerals in conglomerate reservoir was clarified. • The adsorption capacity of polymer and surfactant can be accurately calculated according to the petrophysical volume model. • The N element calibration method was used to determine the occurrence state and content of chemical agent in micro pore after SP binary flooding. • A method of reservoir classification considering the influence of clay minerals and micro-pore structure on the adsorption of SP binary components is established to further EOR.

Structural transformations of charged spherical surfactant micelles upon solubilization of water-insoluble polymer chains in salt-free aqueous solutions

The structural transformations of charged spherical surfactant micelles of potassium oleate upon solubilization of water-insoluble polymer poly(4-vinylpyridine) were studied in salt-free aqueous solutions by several complementary techniques including SANS with contrast variation, NMR (1H and 2D 1H NOESY) spectroscopy, dynamic light scattering, cryo-TEM, and fluorescence spectroscopy. By SANS it was shown that solubilization of polymer in the micelles results in the formation of complexes with necklace structure, where the mean distance between the micelles bound to polymer (beads) is governed by electrostatic repulsion between them. The polymer penetrates deep into the hydrophobic core of the beads and occupies ca. 60% of their volume. As a result, the average number of surfactant ions in the micelles decreases from 60 till 20. The bound charged micelles impart water solubility to the polymer-surfactant system, and it behaves like a polymer coil in a thermodynamically good solvent.

Synergistic Behavior of Anionic Surfactants and Hydrolyzed Polyacrylamide under an Extensional Field: Effect of Hydrophobicity.

Surfactant-polymer interaction has been studied by many academic and industrial researchers. Associative polymers have attracted attention, especially in enhanced oil recovery due to their ability to generate higher resistance than parental polyacrylamide (HPAM) at a lower concentration. The effect of hydrophobicity on the associative polymer-surfactant interaction has been studied through many means including rheology. Previous rheological studies were restricted to shear-based behavior, and no efforts were undertaken to study the effect of hydrophobicity on the extensional rheological behavior of the surfactant-HPAM system. In this work, the extensional behavior of anionic surfactant-polyacrylamide systems was studied for varying levels of hydrophobicity. The concentration of the surfactant used in the surfactant-polymer formulation ranged from 0 to 0.3%, and the polymer concentration was fixed at 1000 ppm. Extensional rheology was performed using a capillary breakup extensional rheometer. Surface tension studies were also conducted. The results revealed that the parental HPAM-surfactant system shows the maximum extensional viscosity for the concentration range studied here. This is contrary to shear behavior reported in the literature, and it appears that electrostatic repulsive interaction associated with HPAM-surfactant systems becomes dominant in the extensional field. Associative polymer-surfactant systems characterized by higher hydrophobicity showed the least maximum extensional viscosity, as opposed to the literature-reported behavior in the shear field. Hydrophobic interaction associated with associative polymer-surfactant systems appears to become weaker in the extensional field.

Effect of methanol on surfactants and surfactant–PEO mixtures

AbstractMethanol–water system possesses unusual interactions, which may affect surfactant self‐assembly. The main objective of this study was to investigate the interactions and aggregation behavior of ionic surfactants sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) and their equimolar catanionic binary mixtures (CAM) and their ternary mixtures with poly(ethylene oxide) (PEO) in aqueous solutions containing different volume percentages of methanol. Conductometry, surface tensiometry, and dynamic light scattering were employed for this purpose. The aggregation in all the systems showed methanol‐dependent patterns. The maximum shifts observed in the critical aggregation concentrations were 5.5, 2.7, 6.3, 4.1, and 4.4 mM, respectively, for SDS, CTAB, CAM, SDS/PEO, and CTAB/PEO systems for variation in MeOH from 5% to 30% v/v. The change in dielectric of the media and chaotropic nature of methanol was responsible for alteration in self‐assembly. The nature of surfactant especially and head group hydrophobicity also played a significant role in the process. The maximum change in area per molecule (i.e., ~4 nm2) occurred for CTAB/PEO system. The aggregation was delayed in surfactant solutions; however, the presence of polymer induced aggregation due to favorable polymer–surfactant interactions involving the surfactant adsorption onto polymer chains and formation of mixed aggregates. The hydrodynamic radii for CTAB/PEO systems, which were nearly 10 times greater than those recorded for SDS/PEO, showed the transition of system to nonspherical aggregated states. In short, the presence of methanol retarded the aggregation in surfactant and surfactant–polymer systems.

Mixtures of cationic guar gum and anionic surfactants as stabilizers of zirconia suspensions

Mixtures of cationic guar gum (CGG) with some anionic surfactants from different chemical groups (hydrocarbon, fluorinated and silicone surfactants) were used as stabilizers of zirconia suspensions. Stabilization processes were analysed using spectrophotometric method, whereas the mechanism of stability was estimated using adsorption process (spectrophotometry, FTIR). The obtained results show that CGG is able to adsorb on the surface of zirconia and also can form complexes with each of the studied anionic surfactants. However, the affinity of these complexes towards the zirconia surface is different, what causes significant differences in stability of the zirconia/CGG/surfactant suspensions. In order to get some information of the structure and charge of the formed complexes the surface tension and the zeta potential measurements were used as supporting techniques. Among the studied polymer-surfactant systems, the complexes between CGG and sodium dodecyl sulphate (SDS) adsorbed on the zirconia surface the most effectively, and the consequence of this phenomenon was the increase of stability in this system.

Surfactant head group and concentration influence on structure and dynamics of gellan gum hydrogels: Crossover from stretched to compressed exponential

AbstractIn the present study, we have investigated the effects of surfactant addition on the structure and dynamics of gellan gum hydrogels. A strong interaction is seen between gellan gum and oppositely charged cationic surfactant, hexadecyltrimethylammonium bromide (CTAB) whereas rather weak or minimal interactions are observed when either anionic surfactant, sodium dodecylsulfate (SDS), or nonionic surfactant, Triton X‐100 is added to the system. The dynamics of the hydrogels was studied, using dynamic light scattering measurements and the heterodyne method was used for data evaluation. The correlation function of parent hydrogel was fitted with a stretched exponential function, while a single plus stretched exponential function was employed to study the dynamics of hydrogel with surfactants and the corresponding relaxation times were appropriately analyzed. An interesting crossover from stretched to compressed exponential was seen when CTAB was added beyond critical micellar concentration to the system, which was not evidenced for the other two surfactants. Ensemble averaged intensity was also analyzed and the general picture that emerges is that the oppositely charged surfactant has the strongest ability to form large associations as oppose to nonionic and like‐charged surfactants. The rheological measurements were carried out to determine the elastic response of the gels over a wide range of frequencies. It was seen that the elastic modulus was dependent on both the surfactant concentration and type. Cationic surfactant increased the elastic modulus markedly as opposed to the nonionic and anionic surfactants. These results may have implications for the use of polymer surfactant systems as potential products.