Surfactant Solubilization Research Articles

Impact of Surfactants on Solution Behavior and Membrane Transport of Amorphous Solid Dispersions.

The purpose of the study was to develop an amorphous solid dispersion (ASD) of a poorly soluble compound (AK100) and investigate the impact of different surfactants on its dissolution, supersaturation and membrane transport. The solubility of the AK100 was determined in crystalline and amorphous form in the absence and presence of three surfactants at different concentrations: sodium dodecyl sulphate (SDS), polysorbate 80 (PS80) and D-α-tocopherol polyethylene glycol succinate (TPGS). The relation between solubility and surfactant solubilization was evaluated using a computational model. The ASD powder was prepared by solvent evaporation for non-sink dissolution experiments with and without the pre-dissolved surfactants. A transport study with Caco-2 cells was conducted to evaluate the impact of surfactants-based formulation on membrane transport. Both the corresponding crystalline and amorphous solubility of AK100 increased linearly as a function of the surfactant concentrations. The supersaturation was maintained for at least three hours in absence of surfactant and in presence of TPGS, whereas supersaturation declined with SDS and PS80. As expected, the membrane flux of the AK100 was higher for the ASD than for the crystalline powder, and further increased with increased concentration of TPGS. The supersaturation ratio based on the activity-based calculation from Caco-2 cells study was always higher than that of the concentration-based one for the amorphous and crystalline forms of AK100. This study shows how additional solubilizing excipients during formulation development can improve the resulting dissolution and phase behavior of supersaturated drug solution.

Limitations and Innovative Application Methods of Surfactants for Solubilization of Poorly Water-Soluble Drugs.

Poor solubility of drugs leads to poor bioavailability and therapeutic efficiency. A large proportion of drugs that are not developed and marketed for use by patients are due to their extremely low solubility. Therefore, improving the solubility of poorly water-soluble drugs is one of the most important aspects of the field of drug research. With the continuous development of more and more formulation techniques and excipient applications, the solubility of poorly water-soluble drugs can be improved to a certain extent to obtain better pharmacokinetics and pharmacodynamics, including pH microenvironment regulation technology, inclusion complex, solid dispersion, nanotechnology, and application of surfactants. However, the most widely used among them is the application of surfactants. This technique can reduce the surface tension, improve wettability, and have a remarkable solubilizing ability after forming micelles. However, surfactants have also been found to possess certain limitations in solubilization. In this review, the factors affecting the solubilization of surfactants and limiting their application have been summarized from several aspects. These factors include drugs, additives, and media. Some ideas to solve these application limitations have also been put forward, which can lay a foundation for the wider application of surfactants in the future.

Formulating additives in thermoresponsive surfactant-based nematic liquid crystals

Abstract Bicelles can be formed by mixing in given mole fractions two ethoxylated alkyl ether carboxylic acid surfactants of very different HLB in water. We determine the effect of adding three of the most used additives in formulation in health- and home care: propylene glycol, glycerol, and ethanol. The effects of additives are determined and compared in a concentrated isotropic phase above the LCST, a pseudo-lamellar phase, and a discotic nematic phase. The two latter are birefringent, and the nematic phase is viscoelastic. Propylene glycol acts as a co-solvent, improving the temperature stability of the nematic phase up to 20 wt% propylene glycol. Further addition of propylene glycol reduces the phase transition temperatures, inducing microstructural changes due to headgroup dehydration and preferential solubilization of the hydrophilic short chain surfactant. Glycerol acts as an anti-solvent, progressively decreasing phase transition temperatures by dehydration of headgroups. Ethanol is a good co-solvent for the surfactant-mixture. Adding up to 5 wt% ethanol increases the temperature stability of the nematic phase. Higher concentrations of ethanol lead to a single isotropic phase with increasingly molecular dissolution of the surfactants. The effect of the considered additives on molecular packing is followed by high resolution X-ray scattering.

Identification of lipid-specific proteins with high-density lipid-immobilized beads.

In biological membranes, lipids often interact with membrane proteins (MPs), regulating the localization and activity of MPs in cells. Although elucidating lipid-MP interactions is critical to comprehend the physiological roles of lipids, a systematic and comprehensive identification of lipid-binding proteins has not been adequately established. Therefore, we report the development of lipid-immobilized beads where lipid molecules were covalently immobilized. Owing to the detergent tolerance, these beads enable screening of water-soluble proteins and MPs, the latter of which typically necessitate surfactants for solubilization. Herein, two sphingolipid species-ceramide and sphingomyelin-which are major constituents of lipid rafts, were immobilized on the beads. We first showed that the density of immobilized lipid molecules on the beads was as high as that of biological lipid membranes. Subsequently, we confirmed that these beads enabled the selective pulldown of known sphingomyelin- or ceramide-binding proteins (lysenin, p24, and CERT) from protein mixtures, including cell lysates. In contrast, commercial sphingomyelin beads, on which lipid molecules are sparsely immobilized through biotin-streptavidin linkage, failed to capture lysenin, a well-known protein that recognizes clustered sphingomyelin molecules. This clearly demonstrates the applicability of our beads for obtaining proteins that recognize not only a single lipid molecule but also lipid clusters or lipid membranes. Finally, we demonstrated the screening of lipid-binding proteins from Neuro2a cell lysates using these beads. This method is expected to significantly contribute to the understanding of interactions between lipids and proteins and to unravel the complexities of lipid diversity.

Experimental upscaling analyses for a surfactant-enhanced in-situ chemical oxidation (S-ISCO) remediation design

Surfactant-enhanced in-situ chemical oxidation (S-ISCO) is an emerging innovative remediation technology for the treatment of dense non-aqueous phase liquids (DNAPLs). S-ISCO combines the solubilization of contaminants by means of surfactants with the chemical oxidation by an oxidizing agent, thus, potentially increasing the efficiency of the state-of-the-art ISCO technique. Scientific investigations are needed to enable the technology transfer for potential field applications based on the development of a remediation design under well-defined boundary conditions.For this purpose, experimental upscaling analyses were performed using the special infrastructure of the research facility for subsurface remediation (VEGAS). Batch tests showed that oxidation of the selected surfactant E-Mulse 3® (EM3) by activated persulfate (Na-PS) reduced the solubilization of the model contaminants 1,4-DCB, naphthalene, and PCE. As a consequence, the processes of contaminant solubilization and degradation were temporally and spatially separated in the developed remediation design.A proof of concept was provided by performing an S-ISCO medium-scale experiment (100 cm length, 70 cm height, 12.5 cm width), with 1,2-DCB as model DNAPL contaminant to be treated. A groundwater circulation well (GCW) was used to inject a 60 g/L Na-PS solution and to effectively mix the reagents. Sampling of the experiment's outflow and the soil material after treatment showed that neither rebound effects nor residual mass loadings on the soil material could be detected after termination of the S-ISCO treatment.To further evaluate the S-ISCO remediation design under field-like conditions, a large-scale S-ISCO experiment was conducted (6 m length, 3 m height, 1 m width), allowing for an extensive sampling campaign to monitor relevant processes. An efficient contaminant removal from the former source zone could be reached by surfactant solubilization, decreasing contaminant levels from initially over 2000 mg/L 1,2-DCB to final concentrations below 5 mg/L 1,2-DCB. The heterogeneously distributed contaminant degradation, implemented by a three-filter GCW, was attributed to density-induced migration processes that impeded an optimal reaction zone. A density-dependent numerical transport could qualitatively match the observations. By comparing different simulation scenarios, an adapted operation of the GCW was established that provides for a more efficient distribution of the density-influenced oxidant injection.

Comparative Interaction of Flavonoid Quercetin with Different Tween Surfactants

For solubilizing the flavonoid Quercetin (Qct), many mediums are adopted. Surfactant solubilization is important among them. In this work, the interaction of Qct with three nonionic tween surfactants, viz., Tween 20, Tween 40, and Tween 80 was investigated. The effect of the length of the carbon chain on the interaction was analyzed by conductometry, infrared spectroscopy, UV–visible spectroscopy, and antioxidant studies. The experimental results suggested that Tween 80 was most efficient out of the three tween surfactants taken for the study. From the conductivity studies the counterion binding constant β was used to calculate various thermodynamic parameters like Gibbs free energy, ΔG0m, enthalpy, ΔH0m, and entropy of micellization, ΔS0m. The order of stability is given as Qct-Tween 80 > Qct-Tween 20 > Qct-Tween 40. The theoretical values also corroborate the same order of interaction with the three surfactants.

Dual Charge Transfer Generated from Stable Mixed-Valence Radical Crystals for Boosting Solar-to-Thermal Conversion.

Realizing dual charge transfer (CT) based on stable organic radicals in one system is a long-sought goal, however, remains challenging. In this work, a stable mixed-valence radical crystal is designed via a surfactant-assisted method, namely TTF-(TTF+• )2 -RC (where TTF = tetrathiafulvalene), containing dual CT interactions. The solubilization of surfactants enables successful co-crystallization of mixed-valence TTF molecules with different polarity in aqueous solutions. Short intermolecular distances between adjacent TTF moieties within TTF-(TTF+• )2 -RC facilitate both inter-valence CT (IVCT) between neutral TTF and TTF+• , and inter-radical CT (IRCT) between two TTF+• in radical π-dimer, which are confirmed by single-crystal X-ray diffraction, solid-state absorption, electron spin resonance measurements, and DFT calculations. Moreover, TTF-(TTF+• )2 -RC reveals an open-shell singlet diradical ground state with the antiferromagnetic coupling of 2J = -657 cm-1 and an unprecedented temperature-dependent magnetic property, manifesting the main monoradical characters of IVCT at 113-203 K while the spin-spin interactions in radical dimers of IRCT are predominant at 263-353 K. Notably, dual CT characters endow TTF-(TTF+• )2 -RC with strong light absorption over the full solar spectrum and outstanding stability. As a result, TTF-(TTF+• )2 -RC exhibits significantly enhanced photothermal property, an increase of 46.6°C within 180 s upon one-sun illumination.

Optical fiber optofluidic laser based on surfactant solubilization of rhodamine B gain in an aqueous solution.

We report a whispering gallery mode (WGM)-based fiber optofluidic laser (FOFL), in which rhodamine B (RhB) in an aqueous surfactant solution of sodium dodecylbenzene sulfonate (SDBS) is used as the laser gain medium. Here, the role of SDBS is to scatter the RhB dye molecules to effectively prevent its self-association in the aqueous solution. Therefore, the fluorescence quantum yield of the used RhB dye is improved due to the enhanced solubilization, which results in a low lasing threshold of ∼2.2 µJ/mm2 when the concentration of SDBS aqueous solution reaches up to 20 mM, on par with or even better than most of the optofluidic dye lasers using RhB as the gain medium in an organic solution. We then establish a model of solubilization capacity of SDBS micelles, which successfully addresses the mechanisms of dye-surfactant interactions in the proposed FOFL system. We further apply this FOFL platform to the case of concentration sensing of the used SDBS, which exhibits a 2-order-of-magnitude improvement in sensitivity compared to the fluorescence measurement due to the signal amplification inherent to the lasing process. The proposed FOFL platform in combination with surfactant solubilization gain medium in an aqueous solution promises to enable chip-scale coherent light sources for various environmental and bio-chemical sensing applications.

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.

Effect of surfactant on pore-scale mobilization characteristics in various pore structure conglomerate for enhanced oil recovery

Surfactant-enhanced mobilization features in various complicated pore structures were rarely investigated. In this work, from the perspective of pore heterogeneity, taking conglomerate with complicated pore-throat distribution as an example, micromodels with three pore structures were fabricated, and polymer and polymer-surfactant (SP) solutions were compared to evaluate the effect of surfactant on the pore-scale mobilization. Furthermore, quantification methods of pore-throat sweep efficiency and recovery were established for the first time through a special image processing workflow. The microfluidics experiment results demonstrated that the solubilization of surfactant could significantly improve the pore-throat displacement efficiency, which contributed to the recovery of SP flooding 6–13% higher than that of polymer flooding. The pore-throat sweep efficiency features at the presence of surfactant varied significantly with displacement pattern. In the displacement pattern of ramified, surfactant would reduce the sweep efficiency of small pore-throat by 7–15% in comparison with polymer flooding, but the favorable displacement efficiency compensated for the difference in pore-throat recovery. In the displacement pattern of compact, surfactant exerted a positive role in expanding sweep efficiency in synergy with polymer, which contributes to promoting the sweep efficiency and recovery in the full range of pore-throat by 7–25%. Last of all, critical driven pore-throat (CDP) was defined, below which pore-throat recovery decreased significantly. The cumulative permeability contribution (CPC) method was utilized to realize CDP generalization in various pore-throat distributions. The CDP of polymer flooding and surfactant flooding corresponded to CPC of 96.21% and 98.71%, respectively. The results play an essential role in understanding how the pore-throat distribution impacts the fluid movement and application of surfactant flooding in the reservoir with complicated pore structures.

Conjugated Cationic Pp-x Formed on g-C3N4 for Photocatalyzed Water Splitting.

Polycationic Pp-x@g-C3N4 composite was synthesized through an in situ polymerization process of N-alkylpyridinium acetylenic alcohol bromide (p-x) above the surface of g-C3N4. The structure of p-0 and the Pp-x@g-C3N4 properties were checked by modern technologies. Photocatalytic tests of Pp-x@g-C3N4 in water splitting unveiled much better Pp-x@g-C3N4 hydrogen evolution activities by comparison with both g-C3N4 and Pp-0. The hydrogen production by Pp-0@g-C3N4 was 1654.5 μmol h-1 g-1, which is ∼26- and 22-fold greater in relation to what g-C3N4 and Pp-0 produced (62.7 and 75.0 μmol h-1 g-1, respectively), suggesting strong bilateral and synergistic interactions of g-C3N4 with Pp-0. Although the lengthening methylene chain in the polymers weakened the hydrogen generation ability of Pp-x@g-C3N4, the conjugated double bonds, solubilization, and dispersion of Pp-x polycationic surfactants made Pp-x@g-C3N4 superior to g-C3N4 in water splitting. Due to the readily available raw materials, a simple way of preparation (starting chemicals to p-0 to Pp-0@g-C3N4), high photocatalysis efficiency, light irritation stability, recyclable ability, and low toxicity, Pp-0@g-C3N4 is a good candidate for water splitting.

Solubilization of surfactant stabilized gold nanoparticles in oil – in – water and water – in – oil microemulsions

W/O and O/W microemulsions were used for determining the solubilization capacity of surfactant stabilized Au nanoparticles (NPs) as metallic nano-pollutants. Tween 80 (emulsifier), hexane/dodecanethiol (oil), and isopropyl alcohol (cosurfactant) were used to prepare microemulsions along with aqueous Au NPs. Different kinds of surfactants were used to produce surfactant stabilized Au NPs. Solubilization studies were carried out by measuring the UV–visible spectra of Au NPs on the basis of their surface plasmon resonance (SPR), dynamic light scattering, and fluorescence measurements to determine the solubilization capacity of aqueous Au NPs. Results indicated that solubilization capacity showed little dependence on the nature of surfactant used for preparing surfactant stabilized Au NPs rather it depended more on the amount of Tween 80 in the preparation of microemulsion. Higher amount of Tween 80 provided greater solubilization capacity of microemulsion to solubilize Au NPs. Stability of the microemulsion was determined from the fluorescence measurements by using fluorescence active surfactant and found that the micromeulsion was stable up to 55 °C for solubilization study. The findings are expected to design microemulsion systems suitable for solubilizing metal industrial effluents.

Enhanced trichloroethylene degradation in the presence of surfactant: Pivotal role of Fe(II)/nZVI catalytic synergy in persulfate system

Trichloroethylene (TCE) removal performance in non-ionic surfactant Tween-80 (TW-80) and anionic surfactant sodium dodecyl sulfate (SDS) involved solution by Fe(II) activated persulfate (PS) was investigated through the strengthening of nanoscale zero valent iron (nZVI). 99.5% removal of TCE could be obtained at the PS/Fe(II)/nZVI/TCE molar ratio of 8/4/4/1 with 1.0 critical micelle concentration (CMC) of TW-80 presence (13 mg L−1), while this value was slightly decreased to 88.3% at the molar ratio of 40/20/20/1 with 1.0 CMC of SDS presence (2.3 g L−1) in 180 min. The addition of nZVI significantly promoted TCE degradation, while TW-80 or SDS definitely inhibited TCE removal. Further, TCE removal declined with TW-80 or SDS concentration increasing from 0 to 10 CMC, and continuously decreased at 20 CMC of TW-80 but elevated TCE removal at 20 CMC of SDS. Tests of radical scavengers revealed that HO and SO4− contributed a major part while O2− had less contribution to TCE degradation in PS/Fe(II)/nZVI system. The dichlorination of TCE in PS/Fe(II)/nZVI system was 94.5% with TW-80 and 97.2% with SDS. In addition, TCE (with TW-80) removal was decreased with the initial pH increase from 3.0 to 11.0, while TCE (with SDS) degradation was always beyond 83% in the initial pH change from 3.0 to 11.0. Moreover, the effects of inorganic anions (Cl−, HCO3−) in the solution were evaluated. Experimental results using the actual groundwater revealed the excellent availability of PS/Fe(II)/nZVI system in remediating TCE contaminated field involved with TW-80 or SDS surfactants. In summary, these findings provide a new direction in remediating groundwater from contaminated sites polluted by chlorinated organic solvents after pretreatment by surfactant solubilization.

Effect of commonly used EOR polymers on low concentration surfactant phase behaviors

High molecular weight polymers are required for the purpose of mobility and conformance control during surfactant chemical flooding. However, they are usually not incorporated in the process of phase behavior tests to screen surfactant formulations. Literature review shows some particular polymers have a boosting effect on surfactant solubilization efficiency. To gain more insight into this subject, we performed phase behavior tests in the presence of four commonly used EOR polymers for low concentration surfactant systems (0.3%). They were two partially hydrolyzed polyacrylamides (HPAM) with different molecular weights, one xanthan gum, and one hydrophobically associating polymer (HAP). Their influence on the optimal salinity, solubilization ratio, quickness of phase equilibration, and middle phase rheological behavior was assessed. The results showed: (1) a decrease of surfactant solubilization efficiency and the optimal salinity was observed with HPAM polymers. This trend became more pronounced as increase of polymer concentration and molecular weight; (2) xanthan seemed to slightly increase the optimal salinity without significantly affecting middle phase volume; (3) both HPAM and xanthan did not delay or quicken the equilibration of various phases compared to the zero polymer case. The analysis of the oil/water solubilization ratios showed HPAM tended to drag water out of the middle phase, while the presence of xanthan increased the water solubilization in the middle phase; (4) the viscosity and rheology of the middle phase microemulsions were very similar for systems containing HPAM, xanthan, and zero polymer. This confirmed the partitioning of polymer molecules in the middle phase was negligible; (5) the association of HAP with surfactants thickened the surfactant-rich phase, which made the phase separation dramatically slow. These phenomena could be explained well by the nature of their molecular structures. For both water-soluble HPAM and xanthan gum, unlike the reported diblock copolymers, they lack the amphiphilic features, which prevents them from adsorbing in the surfactant film. Conversely, the introduction of hydrophobic group into the backbone renders associating polymers some surfactant-like attributes, enabling them to associate with surfactant molecules and affect the surfactant-rich phase behaviors.

Degradation of trichloroethylene in aqueous solution by sodium percarbonate activated with Fe(II)-citric acid complex in the presence of surfactant Tween-80

The degradation performance of trichloroethylene (TCE) by sodium percarbonate (SPC) activated with citric acid (CA) chelated Fe(II) in the presence of nonionic surfactant Tween-80 was investigated. The addition of CA successfully prevented the precipitation of iron and facilitated TCE degradation. However, Tween-80 had an inhibitory effect on TCE degradation mainly due to the competition of ∗OH between Tween-80 and TCE. The effect of SPC and Fe(II) dosage on TCE degradation was also explored and the results displayed that 87.2% of TCE could be degraded in 15 min at the SPC/Fe(II)/CA/TCE molar ratio of 3/4/2/1. Free radical probe tests confirmed that both O2−∗ and ∗OH were generated in the SPC/Fe(II)/CA system. Free radical scavenging tests implied that the degradation of TCE in the SPC/Fe(II)/CA system was mainly attributed to ∗OH, while O2−∗ was only partially involved in the degradation of TCE. In addition, TCE removal was suppressed with the raising of the initial solution pH from 3.0 to 9.0. The actual groundwater (containing Tween-80) tests confirmed that 93.2% of TCE degradation could be achieved at the SPC/Fe(II)/CA/TCE molar ratio of 30/40/10/1 and strongly demonstrated that the SPC/Fe(II)/CA process has potential for the in situ treatment of TCE contaminated groundwater in the presence of surfactant Tween-80. In conclusion, TCE degradation by Fe(II) activated SPC system in the presence of Tween-80 can be significantly enhanced with the addition of CA, and this finding offers an innovative direction for removing chlorinated organic contaminants from groundwater in contaminated site after surfactant solubilization treatment.

Cyclodextrins as Surfactants for Solubilization and Purification of Carbon Nanohorn Aggregates.

Nano- to micrometer-scale surface roughness contributes to the hydrophobicity of materials as discussed often in terms of superhydrophobicity. We report here that as little as 1 wt% of α, β, and γ-cyclodextrins (CDs) can disperse carbon nanohorn aggregates (CNHa) as surfactants in water by binding on their pointed tips. The binding mode was visually demonstrated using single-molecule atomic resolution real-time electron microscopy (SMART-EM). The SMART-EM data provided an estimation of the equilibrium constant of the CD binding to be close to that of adamantane ammonium chloride to β-CD. A qualitative study on the rate of decomplexation of α, β, and γ-CDs from CNHa suggests a substantial mechanistic difference in their binding mode to the CNH tips. A sequence of α-CD complexation and decomplexation allows us to purify CNHa by selectively removing graphitic ball-shaped impurity (GB). Upon treatment with NaNH2 , the purified CNHa produce GB-free amino-CNHa where the tips are functionalized with NH2 groups.

Evaluation of ethoxylated nonionic surfactants for solubilization of chlorinated organic phases: Effects of partitioning loss and macroemulsion formation

Selection of proper surfactants is critical for applying surfactant-enhanced remediation (SER) to sites contaminated with nonaqueous phase liquids (NAPLs). Here, ethoxylated nonionic surfactants (Tween 20, Tween 40, Tween 80, and Triton X-100) were evaluated for their applicability to remedy chlorinated organic phases, chloroform (CF), trichloroethylene (TCE), and tetrachloroethylene (PCE), on the basis of solubilization capacity, partitioning behavior, and macroemulsion formation. The most hydrophilic CF was not relevant for SER applications since excessive surfactant partitioning into CF rendered only few of them available for its solubilization. In contrast, the more hydrophobic TCE and PCE, having moderate surfactant partitioning, were effectively solubilized. Among Tween surfactants, a more hydrophobic surfactant showed a larger solubilization potential for both chloroethylenes, but it suffered from a greater partitioning loss. Depending on the type and extent of NAPL contaminations, thus, a prior consideration should be given to either solubilization capacity or partitioning loss when selecting the optimal Tween surfactant. Compared to Tween surfactants, the more hydrophobic Triton X-100 showed greater partitioning losses into all three NAPLs. Of particular, its partitioning into CF and TCE was nearly complete, making impractical its application to the remediation of both organic liquids. The formation of macroemulsions, characterized by a high turbidity, may significantly deteriorate SER applicability by producing undesirable flows in aquifers. Their formation became more problematic with the increasing surfactant hydrophilicity and the increasing NAPL hydrophobicity. When these combinations are applied, it is critical to keep such surfactant concentrations as to exploit the solubilization potential but not to cause the macroemulsion formation.

Hydrocarbon Recovery From Oil Sands by Cyclic Surfactant Solubilization in Single-Phase Microemulsions

Extra heavy crude oil (bitumen) reserves represent a significant part of the energy resources found all over the world. In Canada, the “oil sands” deposits are typically unconsolidated, water-wet media where current methods of recovery, such as open pit mining, steam-assisted gravity drainage (SAGD), vapor extraction, cold heavy oil production with sand, etc., are controversial due to adverse effect on environment. Chemical enhanced oil recovery (cEOR) techniques have been applied as alternatives but have limited success and contradictory results. An alternative method is described in this paper, which relies on the application of single-phase microemulsion to achieve extremely high solubilization. The produced microemulsion will be less viscous than oil, eliminating the need for solvent addition. Produced microemulsion can be separated to recover surfactant for re-injection. The work in this paper discusses phase behavior experiments and a flow experiment to prove the concept that single-phase microemulsions could be used to recover extra-heavy oils. Phase behavior experiments showed that the mixture of alcohol propoxysulfate, sodium dioctyl sulfosuccinate, sodium carbonate, and tri-ethylene glycol monobutyl ether results in single-phase microemulsion with extra-heavy crude. A flow experiment conducted with the same composition produced only single-phase microemulsion leading to 74% recovery of the original oil in place from a synthetic oil sand. Future experiments will be focused on optimizing the formulation and testing with actual oil sands samples.

Emulsification, solubilization, and detergency behaviors of homogeneous polyoxypropylene-polyoxyethylene alkyl ether type nonionic surfactants

The emulsification and solubilization properties and detergency behaviors were investigated using homogeneous polyoxypropylene-polyoxyethylene (PO-EO) alkyl ether type nonionic surfactants (C12EOxPO3, where x represents EO chain lengths of 6 and 8, and C12 and PO3 indicate the dodecyl chain and single trioxypropylene chain, respectively) and polyoxyethylene (EO) alkyl ether type nonionic surfactants (C12EOx, x = 6 and 8). These nonionic surfactants possess single EO and PO chain lengths without a distribution. An oil-in-water (O/W) type emulsion prepared using mixtures of nonionic surfactant C12EOxPO3 or C12EOx solutions and squalane was shown to be stable in the order of C12EO6PO3 << C12EO6 < C12EO8PO3 < C12EO8. The introduction of a PO chain to the terminal hydroxy group of the EO chain lowers the emulsion stability owing to the difficult orientation of a complex structure such as the hydrophobic alkyl chain–hydrophilic EO chain-hydrophobic PO chain at the water/oil interface. The solubilization of these nonionic surfactants was shown to be higher for stearic acid than for naphthalene as a solubilizate. The molar solubilization ratio (MSR) for naphthalene and stearic acid was the highest for C12EO6PO3 and C12EO8PO3, respectively. The removal of stearic acid from a gold substrate evaluated using a quartz crystal microbalance (detergency) was the highest for C12EO6PO3 among the four surfactants applied. Thus, no significant correlation was found among the emulsification, solubilization, and detergency behaviors ; however, a high performance for each objective was obtained by controlling both the EO chain length and the introduction of a PO chain.

Reversible Solubilization of Pyrene by a Gas Switchable Surfactant Investigated by Molecular Dynamics Simulation.

The reversible solubilization behavior of pyrene by a CO2/N2 switchable surfactant (named N'-dodecyl- N, N-dimethylacetamidinium bicarbonate (DDAB)) was investigated with molecular dynamics (MD) simulations. We first individually simulated the aggregation of the inactive surfactant N'-dodecyl- N, N-dimethylacetamidines (DDA) and effective surfactant DDAB in water. Detailed structural properties analysis showed that DDAB molecules aggregated into a micelle, while the aggregation of DDA molecules was considered to be an oil droplet that was separated from the water phase. MD simulations revealed that pyrene molecule was solubilized in the interior hydrophobic region of the micelle as expected. Pyrene was adsorbed on the surface of the oil droplet which is due to the dense packing of DDA molecules inside the oil droplet. The simulated release process showed that the solubilized pyrene in the interior was squeezed out when the micelle was changed to an oil droplet. Reduced density gradient (RDG) function was used to study the weak interactions and explore the molecular driving force behind the reversible solubilization. The results demonstrated that repulsion effects of water molecules on the DDA headgroups play an important role on the pyrene release. Because of the persistent molecular motion of DDA molecules into the droplet center, pyrene was finally repelled out of the oil droplet. Our study provided a molecular mechanism into the reversible solubilization of a gas-controlled switchable surfactant. This is expected to be useful for surfactant-enhanced remediation (SER) experiments.