Phase Behavior Of Surfactants Research Articles

Sequence dependence of critical properties for two-letter chains.

Histogram-reweighting grand canonical Monte Carlo simulations are used to obtain the critical properties of lattice chains composed of solvophilic and solvophobic monomers. The model is a modification of one proposed by Larson et al. [J. Chem. Phys. 83, 2411 (1985)], lowering the "contrast" between beads of different types to prevent aggregation into finite-size micelles that would mask true phase separation between bulk high- and low-density phases. Oligomeric chains of lengths between 5 and 24 beads are studied. Mixed-field finite-size scaling methods are used to obtain the critical properties with typical relative accuracies of better than 10-4 for the critical temperature and 10-3 for the critical volume fraction. Diblock chains are found to have lower critical temperatures and volume fractions relative to the corresponding homopolymers. The addition of solvophilic blocks of increasing length to a fixed-length solvophobic segment results in a decrease of both the critical temperature and the critical volume fraction, with an eventual slow asymptotic approach to the long-chain limiting behavior. Moving a single solvophobic or solvophilic bead along a chain leads to a minimum or maximum in the critical temperature, with no change in the critical volume fraction. Chains of identical length and composition have a significant spread in their critical properties, depending on their precise sequence. The present study has implications for understanding biomolecular phase separation and for developing design rules for synthetic polymers with specific phase separation properties. It also provides data potentially useful for the further development of theoretical models for polymer and surfactant phase behavior.

Impact of surfactant polydispersity on the phase and flow behavior in water: the case of Sodium Lauryl Ether Sulfate

This study delves into the impact of molecular polydispersity on the phase behavior of Sodium Lauryl Ether Sulfate (SLES) surfactant, aiming to deepen understanding of its implications for fundamental science and industrial applications. SLE3S is utilized as a model compound: a comprehensive characterization of molecular polydispersity is conducted using Gas Chromatography–Mass Spectrometry and Nuclear Magnetic Resonance spectroscopy, juxtaposing the findings with those for SLE1S.Our comprehensive investigative approach entails: (i) employing Time-Lapse dissolution experiments in microchannel geometries to observe the dissolution and phase transitions; (ii) utilizing polarized light microscopy, confocal microscopy, and Small Angle X-ray Scattering for microstructure identification assessments; (iii) conducting rheological evaluations at various concentrations and temperatures to determine their effects on the surfactant properties.The findings reveal that SLE3S, being more polydisperse, demonstrates complex phase behavior not observed in the less polydisperse SLE1S. Notably, SLE3S exhibits a unique concentration domain, corresponding to a concentration of about 60 %wt, where hexagonal (H), cubic, and lamellar (Lα) phases coexist, resulting in highly viscoelastic heterogeneous mixtures. This behavior is attributed to the local segregation of surfactant components with varying polarity, underscoring the crucial role of molecular polydispersity in the phase behavior of SLES surfactants.

Phase behavior of lyotropic alkyl thioglycolipid surfactants: Effects of sugar headgroup and alkyl tail length

AbstractThe lyotropic properties of alkyl thioglycosides with varying sugar headgroup (lactose, cellobiose, maltose, galactose, or glucose) and alkyl chain length (octyl, decyl, or dodecyl chains) are investigated by surface tensiometry, visual observation, and fluorescence spectroscopy. The results substantiate that the glycosidic S‐linkage confers considerably different solution aggregation behavior on these surfactants relative to their O‐linked counterparts, where the properties of the latter are known. The materials properties of the aggregated structures from the alkyl thioglycosides vary considerably. Micelles are formed by octyl thiocellobioside and all alkyl thiomaltosides. Turbid aggregate solutions are formed by the alkyl thioglucosides and octyl thiogalactoside, whereas the longer chain alkyl thiogalactosides are minimally soluble. Fluorescence spectroscopy of these systems confirms their aggregation in lamellar‐like structures. The alkyl thiocellobiosides and alkyl thiolactosides form hydrogels from these low‐molecular weight materials at concentrations almost an order of magnitude lower than gels using other low‐molecular weight materials. Here, hydrogels form at concentrations <0.3 wt% with some forming hydrogels at concentrations as low as 0.03 wt% from alkyl thiocellobiosides and thiolactosides, with hydrogel properties differing significantly with this slight change in the sugar headgroup. Alkyl thiocellobiosides form a nanofiber network and alkyl thiolactosides form globular hydrogels. Overall, these results clearly document materials properties that can readily be controlled and designed depending on molecular structure.

Dynamic diffusive interfacial transport (D-DIT): A novel quantitative swelling technique for developing binary phase diagrams of aqueous surfactant systems.

Current methods to develop surfactant phase diagrams are time-intensive and fail to capture the kinetics of phase evolution. Here, the design and performance of a quantitative swelling technique to study the dynamic phase behavior of surfactants are described. The instrument combines cross-polarized optical and short-wave infrared imaging to enable high-resolution, high-throughput, and in situ identification of phases and water compositions. Data across the entire composition spectrum for the dynamics and phase evolution of a binary aqueous non-ionic surfactant solution at two isotherms are presented. This instrument provides pathways to develop non-equilibrium phase diagrams of surfactant systems-critical to predicting the outcomes of formulation and processing. It can be applied to study time-dependent material relationships across a diverse range of materials and processes, including the dissolution of surfactant droplets and the drying of aqueous polymer films.

Phase behavior, micellization and rheology of erucic acid-based ionic liquid surfactant in deep eutectic solvents

Fatty acid-based ionic liquid surfactants have attracted significant attention due to their environmental friendliness, showing significant potential in some specific applications (e.g., personal & house care products). Deep eutectic solvents (DES) are a kind of new green and promising solvent. However, the self-assembly of ultra-long-chain fatty acid-based ionic liquid surfactants in DES has rarely been reported to date. In this paper, erucic choline (ErCho), as a representative of ultra-long-chain ionic liquid surfactants, was synthesized and characterized, and then its micellization behavior in three different DES (ChGly, ChEG, and ChPh, which were obtained by mixing glycerol, ethylene glycol, phenol, and choline chloride in a 2:1 M ratio) was investigated. ErCho can self-assemble into micelles in DES, as well as in water, but a relatively larger critical micelle concentration (cmc) was obtained in DES due to a small hydrophobic association. The hydrophobic association of ErCho in ChGly was the smallest, and the standard free energy of micellization per mole of monomer unit was the largest (-37.67 kJ·mol−1). However, at high shear rates, typical shear-thinning was observed in the ChGly solution of ErCho, showing pseudoplastic fluids behavior, which was not found in ChEG, ChPh, and H2O. This reflects the presence of large aggregates, and cryo-TEM observation confirmed the formation of wormlike micelles in the ChGly solution of ErCho with a small flow activation energy (∼43 kJ·mol−1). In addition, ErCho in ChGly solution can further evolve into a hexagonal phase, and then to lamellar crystalline phases upon increasing concentration.

Can Machine Learning Predict the Phase Behavior of Surfactants?

We explore the prediction of surfactant phase behavior using state-of-the-art machine learning methods, using a data set for twenty-three nonionic surfactants. Most machine learning classifiers we tested are capable of filling in missing data in a partially complete data set. However, strong data bias and a lack of chemical space information generally lead to poorer results for entire de novo phase diagram prediction. Although some machine learning classifiers perform better than others, these observations are largely robust to the particular choice of algorithm. Finally, we explore how de novo phase diagram prediction can be improved by the inclusion of observations from state points sampled by an analogy to commonly used experimental protocols. Our results indicate what factors should be considered when preparing for machine learning prediction of surfactant phase behavior in future studies.

Phase transitions of the pulmonary surfactant film at the perfluorocarbon-water interface

Pulmonary surfactant is a lipid-protein complex that forms a thin film at the air-water surface of the lungs. This surfactant film defines the elastic recoil and respiratory mechanics of the lungs. One generally accepted rationale of using oxygenated perfluorocarbon (PFC) as a respiratory medium in liquid ventilation is to take advantage of its low surface tensions (14–18 mN/m), which was believed to make PFC an ideal replacement of the exogenous surfactant. Compared with the extensive studies of the phospholipid phase behavior of the pulmonary surfactant film at the air-water surface, its phase behavior at the PFC-water interface is essentially unknown. Here, we reported the first detailed biophysical study of phospholipid phase transitions in two animal-derived natural pulmonary surfactant films, Infasurf and Survanta, at the PFC-water interface using constrained drop surfactometry. Constrained drop surfactometry allows in situ Langmuir-Blodgett transfer from the PFC-water interface, thus permitting direct visualization of lipid polymorphism in pulmonary surfactant films using atomic force microscopy. Our data suggested that regardless of its low surface tension, the PFC cannot be used as a replacement of pulmonary surfactant in liquid ventilation where the air-water surface of the lungs is replaced with the PFC-water interface that features an intrinsically high interfacial tension. The pulmonary surfactant film at the PFC-water interface undergoes continuous phase transitions at surface pressures less than the equilibrium spreading pressure of 50 mN/m and a monolayer-to-multilayer transition above this critical pressure. These results provided not only novel biophysical insight into the phase behavior of natural pulmonary surfactant at the oil-water interface but also translational implications into the further development of liquid ventilation and liquid breathing techniques.

Investigating the Phase Behavior of Viscoelastic Surfactant with Squalene and Crude Oil Systems at High Temperature

Investigating the Phase Behavior of Viscoelastic Surfactant with Squalene and Crude Oil Systems at High Temperature

Phase Behavior of Alkyl Ethoxylate Surfactants in a Dissipative Particle Dynamics Model.

We present a dissipative particle dynamics (DPD) model capable of capturing the liquid state phase behavior of nonionic surfactants from the alkyl ethoxylate (CnEm) family. The model is based upon our recent work [Anderson et al. J. Chem. Phys. 2017, 147, 094503] but adopts tighter control of the molecular structure by setting the bond angles with guidance from molecular dynamics simulations. Changes to the geometry of the surfactants were shown to have little effect on the predicted micelle properties of sampled surfactants, or the water-octanol partition coefficients of small molecules, when compared to the original work. With these modifications the model is capable of reproducing the binary water-surfactant phase behavior of nine surfactants (C8E4, C8E5, C8E6, C10E4, C10E6, C10E8, C12E6, C12E8, and C12E12) with a good degree of accuracy.

Rheology and Phase Behavior of Surfactant–Oil–Water Systems and Their Relationship with O/W Nano-Emulsion’s Characteristics Obtained by Dilution

In order to study the relationship between the rheology of a surfactant’s concentrated dispersions and the oil and water liquid crystals from which O/W nanoemulsions (NEs) can be produced by water dilution, the phase diagram of a model SOW (surfactant–oil–water) system was constructed. The dispersion’s compositions to be characterized by rheology were chosen in the diagram’s regions that contain liquid crystal phases. For this, the dilution lines S/O = 25/75, 55/45, and 70/30 with a water content of 20 and 40 wt% (corresponding to surfactant concentrations between 15 and 55 wt%) were chosen. By adding these dispersions to a water pool, NEs were obtained, and it was shown that droplet size distribution depends on the amount of the liquid crystal phase in the initial dispersion and its rheology. The study of the oscillatory amplitude of the dispersion showed a linear viscoelastic plateau (G’ > G”) and a softening deformation region (G” > G’), indicating a viscoelastic behavior of the dispersions. The study was carried out at a constant temperature of 30 °C, and the results show that rheological characterization by itself is not enough to predict that monomodal droplet distributions are obtained. However, the presence and quantity of lamellar liquid crystal phase are important to obtain monodisperse and kinetically stable NEs.

Predicting surfactant phase behavior with a molecularly informed field theory

HypothesisThe computational study of surfactants and self-assembly is challenging because 1) models need to reflect chemistry-specific interactions, and 2) self-assembled structures are difficult to equilibrate with conventional molecular dynamics. We propose to overcome these challenges with a multiscale simulation approach where relative entropy minimization transfers chemically-detailed information from all-atom (AA) simulations to coarse-grained (CG) models that can be simulated using field-theoretic methods. Field-theoretic simulations are not limited by intrinsic physical time scales like diffusion and allow for rigorous equilibration via free energy minimization. This approach should enable the study of properties that are difficult to obtain by particle-based simulations. Simulation WorkWe apply this workflow to sodium dodecylsulfate. To ensure chemical fidelity we present an AA force field calibrated against interfacial tension experiments. We generate CG models from AA simulation trajectories and show that particle-based and field-theoretic simulations of the CG model reproduce AA simulations and experimental measurements. FindingsThe workflow captures the complex balance of interactions in a multicomponent system ultimately described by an atomistic model. The resulting CG models can study complex 3D phases like double or alternating gyroids, and reproduce salt effects on properties like aggregation number and shape transitions.

Surfactant evaluation for enhanced oil recovery: Phase behavior and interfacial tension

Abstract Surfactant flooding is one of the successful techniques employed in enhanced oil recovery (EOR) to extract the remaining original oil in place after primary and secondary recoveries are performed. Selection of the right EOR surfactant is an important but demanding task due to a series of screening procedures that need to be executed to have a comprehensive evaluation. This article presents the experimental work done on the initial screening of ten surfactants from three different classes, namely nonionic, anionic, and amphoteric. The screening was completed with three consecutive series of testing, which are surfactant compatibility, phase behavior, and interfacial tension (IFT). Results showed that an anionic surfactant, sodium decylglucoside hydroxypropyl phosphate, passed all tests with the lowest IFT value of 8 × 10−3 mN/m at 0.1 wt% of surfactant concentration.

Study of the efficiency of technical grade nonionic surfactants

AbstractParameters concerning the microemulsion phase behavior of nonionic surfactants of the alkyl polyglycol ether type have extensively been investigated in the last years. By studying these, essential parameters for future applications can be determined. Especially in the field of enhanced oil recovery, lubricants, and cosmetic applications these parameters are of special interest. In this work, the influence of technical grade nonionic surfactants on the phase behavior and the resulting surfactant efficiency has been studied. For this, the alkyl chain length, the degree, type, and order of alkoxylation of the surfactant have been varied. The investigation of these parameters has been conducted by measuring the phase behavior via the Kahlweit fish diagram. It has been found that varying the C‐chain length has a great impact on the efficiency, whereas the influence of the ethoxylation degree is minor. By the introduction of propylene oxide, the efficiency has been improved significantly. Additionally, it is important to have the right order of alkoxylation. If the fatty alcohol is first ethoxylated and afterwards propoxylated the efficiency is significantly decreased.

Synthesis and performance evaluation of polymeric surfactant from rice husk and polyethylene glycol for the enhanced oil recovery process

A tertiary recovery technique is needed to recover the remained oil in the oil field after primary and secondary recoveries, which can only recover approximately 30–50% of the total oil. This study investigated the synthesized polymeric surfactants from rice husk and polyethylene glycol (PEG) for the enhanced oil recovery (EOR) process as a tertiary recovery technique. The rice husk was used as sodium lignosulfonate (SLS) surfactant production feedstock. SLS-PEG polymer surfactant from rice husk has not been widely studied, especially for the EOR process. This study has comprehensively investigated the effect of PEG concentration on the polymeric surfactant properties. The surfactants were characterized using Fourier transform-Infrared (FT-IR) analysis. Several other tests were also conducted, including surfactant compatibility, viscosity, thermal stability, interfacial tension (IFT), and phase behavior. It was found that the PEG introduction to the SLS surfactant could increase the hydrophilic property of the polymeric surfactant due to the presence of the C−O−C group. In addition, the IFT value decreased with the increase in the PEG concentration due to the increase in the hydrophilic property. However, the IFT value decreased when the PEG concentration was too high. The lowest IFT value was obtained at the SLS to PEG ratio of 1:0.8. It produced the highest increase in the additional recovered oil after brine flooding. The results showed that the rice husk, which is agricultural waste, could be utilized as a feedstock for the surfactant production.

Microemulsion interface model for chemical enhanced oil recovery design

The surfactant phase behavior laboratory test for chemical enhanced oil recovery (EOR) formulation design is time consuming. However, it is possible to use computational chemistry simulation to minimize the duration. The only known non-empirical approach to predict surfactant phase behavior is by surface tension analysis, but the optimum phase behavior boundary is unclear and its applicability in actual complex crude oil is unproven. This research overcomes these issues by developing a microemulsion interface model using digital oil model with accurate representation of atomistic components of actual crude oil as inputs to the simulation. The microemulsion interface model is developed based on physical chemistry of surface tension and torque concepts coupled with solution of interface bending rigidity in relation to surfactant solubilization and interface energy. The model is implemented in coarse-grained molecular dynamics simulation technique. The microemulsion interface model is verified with surfactant phase behavior laboratory data using actual crude oil. Good agreement for 12 out of 14 chemical EOR formulations between simulations and phase behavior laboratory results is achieved. This indicates that the main characteristics and physics of the formation of optimal microemulsion were captured correctly in the microemulsion interface model. The duration for surfactant phase behavior determination can be reduced from 14 days in laboratory down to 1.5 day by using the microemulsion interface model, resulting in 90%-time reduction. This faster and more informed formulation development process can minimize time and costly resources as chemical EOR formulations proceed into field implementation.

Phase Behaviour, Functionality, and Physicochemical Characteristics of Glycolipid Surfactants of Microbial Origin.

Growing demand for biosurfactants as environmentally friendly counterparts of chemically derived surfactants enhances the extensive search for surface-active compounds of biological (microbial) origin. The understanding of the physicochemical properties of biosurfactants such as surface tension reduction, dispersion, emulsifying, foaming or micelle formation is essential for the successful application of biosurfactants in many branches of industry. Glycolipids, which belong to the class of low molecular weight surfactants are currently gaining a lot of interest for industrial applications. For this reason, we focus mainly on this class of biosurfactants with particular emphasis on rhamnolipids and sophorolipids, the most studied of the glycolipids.

Study of sodium electrolytes on phase behavior of the anionic surfactant/alcohol/model oil system and its application for alkaline-surfactant flooding formulation design

In this study, the phase behavior of several anionic surfactants, i.e., one internal olefin sulfonate, the sodium dodecyl sulfate and the dodecyl benzene sulfonate, were conducted to investigate the influence of different sodium electrolytes on the optimal salinity of the anionic surfactant/alcohol/model oil system. The sodium activity at the optimal salinity was calculated by the PHREEQC software, which was found to be equal between different sodium electrolytes. Noticeably, the solubilization parameter of water or oil at the optimal salinity was not influenced by the anions, but largely dependent on the alcohol type, the oil type and the temperature. Furthermore, oleic acid was added into model oil to simulate the acid components in crude oil. The phase behavior results indicated that a larger fraction of oleic acid was active at higher pH with sodium hydroxide (NaOH), however, its solubilization parameter at optimal salinity was lower compared to that using sodium carbonate (Na2CO3). The phase behavior of alkali/crude oil was also performed by mixing different alkalis with a crude oil sample that consisted of high contents of water-soluble active soaps. It is found that the soap generated by NaOH is more lipophilic than that generated by Na2CO3. When sodium activity is used, the optimal salinity of alkali/surfactant/crude oil system can be accurately predicted by the improved mixing rule correlation. The findings of this study would be helpful for us to rapidly select the optimum formulation for alkaline/surfactant flooding process.

Geometric features in lyotropic liquid crystalline phase transitions observed in aqueous surfactant systems

Lyotropic liquid crystalline phases are widely known to be formed in aqueous surfactant mixtures. Although the phase behavior of several surfactants has been elucidated in the past years, a striking absence of detailed discussion on how molecular geometric parameters vary as different liquid crystals are formed is consistently seen in literature. The current work aimed to partially fill this gap, by determining how several structural parameters changed in a variety of phase transitions previously observed in aqueous surfactant binary and ternary mixtures. The main findings reveal that the cell parameter dimensions are strongly correlated with the packing fraction of small aggregates in each phase; the folding and interpenetration of surfactant hydrocarbon chains are most likely to happen in phases with lower curvature, and can greatly affect other structural parameters; added components can alter the aqueous surfactant phase behavior at different extents; and highly ordered phases are favored by a substantial decrease in the cross-sectional areas per surfactant; among others. The obtained results enable important knowledge on lyotropic liquid crystal formation, in addition to providing detailed information on how to control and obtain such phases, thus prospecting new insights in areas where they are highly desired.

Mixed micellization of cationic/anionic amino acid surfactants: Synergistic effect of sodium lauroyl glutamate and alkyl tri-methyl ammonium chloride

In the cleaning field of the cosmetics industry, amino acid surfactants with low irritation and degradability have attracted more and more attention. However, in the actual application system, the amino acid type surfactant has the application difficulty that is not easy to thicken. In this study, the surface activities and application of the surfactant mixtures containing the cationic surfactant dodecyl tri-methyl ammonium chloride (DTAC) and anionic amino acid surfactant sodium lauroyl glutamate (SLG) (cationic/anionic amino acid surfactant system) were systematically studied, which will provide theoretical guidance for practical applications. First, the surface tension of the cationic/anionic amino acid surfactant system was measured, and the CMC value, interaction parameters, Gibbs free energy and other data were obtained. From this, the behavior characteristics of the adsorption and aggregation of SLG and DTAC in the solution can be judged. Then through dynamic light scattering instrument, rheometer, polarizing microscope, etc., we analyze the phase behavior of the cationic/anionic amino acid surfactant system under different compound ratios and different concentrations, and draw a pseudo-ternary phase diagram. Finally, the influence of the length of the hydrophobic chain of cationic surfactants on the phase behavior of amino acid surfactants was investigated. Experiments have found that the addition of cationic surfactant DTAC can significantly reduce the CMC value of the SLG system, and the CMC changes with the increase of the SLG ratio as follows: first decrease and then increase. The interaction parameters show that DTAC and SLG have a strong interaction. Contrary to the phenomenon of precipitation after the compounding of conventional cationic/anionic surfactants, the compounding of DTAC and SLG increases the solubility, reduces the Krafft point of SLG, and increases the application performance. At the same time, the problem of difficult control of the viscosity of the amino acid surfactant system has also been better solved. DTAC and SLG form a worm-like mixed micelle, which has a higher and controllable viscosity. Finally, it was found that changing the hydrophobic chain length of cationic surfactants has a direct effect on the viscosity of the system.

Enhanced recovery of a viscous oil with a novel surfactant

Steam-based recovery methods are usually employed to recover heavy and viscous oils, but they are not efficient in deep and thin oil reservoirs. Chemical flooding is studied here to improve recovery of a viscous oil (about 300 cp at the reservoir temperature of 70 °C) from a thin, high permeability, unconsolidated reservoir. A large number of novel short-hydrophobe based surfactants were designed and synthesized. As these surfactants do not require expensive aliphatic alcohols for their synthesis, they are likely to be less costly than conventional anionic surfactants. Only phenol hydrophobe-based non-ionic surfactants with varying number of propylene oxide (PO) and ethylene oxide (EO) groups are discussed in this paper. These surfactant molecules were investigated for their aqueous stability, interfacial tensions (IFT) with a viscous crude oil, and oil recovery from sandpack or sandstone cores. Surfactant phase behavior experiments with viscous crude oil showed low IFT (not ultralow) for single surfactant systems. A chemical formulation using only a single surfactant (Phenol-7PO-15EO) was chosen for corefloods in sandpacks and sandstone cores. Water flood recovered about half of the original oil and reduced the oil saturation to about 48% in the high permeability sandpacks. The tertiary surfactant polymer flood with Phenol-7PO-15EO increased the cumulative recovery to 99% for sandpacks. The oil recovery was insensitive to injection brine salinity in the range studied. As the permeability decreased, the tertiary oil recovery decreased. Surfactant-polymer formulations with this surfactant can be recommended for high permeability sandstone reservoirs with viscous oils, but not for sub-Darcy sandstones.