Properties Of Microemulsions Research Articles

From nano to macro: Hierarchical platinum superstructures synthesized using bicontinuous microemulsion for hydrogen evolution reaction

The possibility to harness the intrinsic properties of bicontinuous microemulsions (BCME) has led to their application as nanocages in the synthesis of nanocoral-shaped Pt hierarchical superstructures (PtHSs). We employed two different platinum precursors (oil-soluble and water-soluble) and sodium borohydride (NaBH4) was used as reducing agent. PtHSs were observed to be pure and nanocrystalline, with small crystallite size (4.5–6.5 nm). XPS showed that the nanostructures are composed of Pt (0). The electrochemical surface areas obtained were 8.7 m2/g, 35.1 m2/g and 20.9 m2/g for PtH–O (synthesized using oil-soluble precursor), PtH-A2 and PtH-A4 (synthesized using 2 and 4% water-soluble Pt precursor), respectively. Linear sweep voltammetry (LSV), Tafel plots and electrochemical impedance spectroscopy (EIS) were used to study the hydrogen evolution reaction process. PtH-A2 showed an overpotential of 68 mV at 10 mA cm−2, a Tafel slope of 30 mV dec−1 and a low charge transfer resistance of 3.39 Ω. The stability of the PtHSs was tested before and after 1000 LSV cycles with minimal loss of current density. The improved electrochemical properties recorded, are due to the unique Pt hierarchical superstructure, which is key for the electrocatalytic performance. Through this research, the “template effect” of bicontinuous microemulsions towards the synthesis of metallic hierarchical superstructures is demonstrated for the first time.

Low-tension gas process in high-salinity and low-permeability reservoirs

Polymer-based EOR methods in low-permeability reservoirs face injectivity issues and increased fracturing due to near wellbore plugging, as well as high-pressure gradients in these reservoirs. Polymer may cause pore blockage and undergo shear degradation and even oxidative degradation at high temperatures in the presence of very hard brine. Low-tension gas (LTG) flooding has the potential to be applied successfully for low-permeability carbonate reservoirs even in the presence of high formation brine salinity. In LTG flooding, the interfacial tension between oil and water is reduced to ultra-low values (10−3 dyne/cm) by injecting an optimized surfactant formulation to maximize mobilization of residual oil post-waterflood. Gas (nitrogen, hydrocarbon gases or CO2) is co-injected along with the surfactant slug to generate in situ foam which reduces the mobility ratio between the displaced (oil) and displacing phases, thus improving the displacement efficiency of the oil. In this work, the mechanism governing LTG flooding in low-permeability, high-salinity reservoirs was studied at a microscopic level using microemulsion properties and on a macroscopic scale by laboratory-scale coreflooding experiments. The main injection parameters studied were injected slug salinity and the interrelation between surfactant concentration and injected foam quality, and how they influence oil mobilization and displacement efficiency. Qualitative assessment of the results was performed by studying oil recovery, oil fractional flow, oil bank breakthrough and effluent salinity and pressure drop characteristics.

Microemulsions in Sodium Dodecyl Sulfate–1-Butanol–Extractant–Kerosene–Water Systems for Extracting Nonferrous Metals from Oxide Raw Materials

Areas of existence and properties of extractant-containing microemulsions in sodium dodecyl sulfate–1-butanol–extractant–kerosene–water systems in the presence of such extractants as caproic acid, di(2-ethylhexyl) hydrogen phosphate, and tributyl phosphate–acetic acid mixture were studied. The possibility of using a sodium dodecyl sulfate microemulsion containing the chosen extractants for extracting nonferrous metals from oxide raw materials was demonstrated by the example of a model system with CuO. The highest degrees of the copper recovery are reached with the microemulsion containing 2.00 M caproic acid or 0.25 M di(2-ethylhexyl) hydrogen phosphate.

Properties and Phase Behavior of Water-in-Diesel Microemulsion Fuels Stabilized by Nonionic Surfactants in Combination with Aliphatic Alcohol

We investigate the properties and phase behavior of the water–diesel fuel–Neonol AF 9-6/2-ethylhexanol system, which is regarded as a promising microemulsion fuel. A pseudoternary diagram of the system has been obtained. In the diesel fuel/water (DF/W) ratio ranging from 98:2 to 50:50 and the emulsifier concentration of 8–40 vol %, a region of microemulsions has been distinguished, generating particular interest as an alternative fuel. In the region under study, a reverse micellar phase L2 has existed predominantly. Fish-cut diagrams have been obtained for the DF/W ratios in the emulsifier concentration–temperature coordinates. An increase in the water fraction in microemulsions significantly has narrowed the range of their stability. The critical changes of microemulsion properties have been identified using the fish-cut diagrams. We have established the empirical relationship among the phase inversion temperature, the emulsifier concentration in the phase inversion point, and the water fraction in micro...

Molecular Dynamics Simulation Insight into Interfacial Stability and Fluidity Properties of Microemulsions.

Although the interfacial properties of microemulsions have been extensively studied in both experimental and simulation research studies, the molecular mechanisms of stability and fluidity about microemulsion are still poorly understood. Herein, we report a molecular dynamics simulation study to elaborate the motion of an emulsion droplet involving dichain surfactant Aerosol OT (AOT) and its dynamics evolution at the oil-water interface. By varying the concentrations of AOT, we show that the interfacial thickness and emulsification rate display a piecewise change as the interfacial coverage increases and the W/O emulsion is more stable than the O/W one while O/W emulsion presents better fluidity. In addition, the dispersed system combined with water/AOT/n-heptane tends to form a W/O microemulsion instead of an O/W microemulsion due to the structural collapse of the latter. This work provides a molecular understanding of microemulsion interfacial stability and fluidity.

Interfacial H-Bond Dynamics in Reverse Micelles: The Role of Surfactant Heterogeneity.

Characterizing the hydrogen bond structure and dynamics at surfactant interfaces is essential for understanding how microscopic interactions translate to bulk microemulsion properties. Heterogeneous blends containing tens or hundreds of surfactants are common in the industry, but the most fundamental studies have been carried out on micelles composed of a single surfactant species. Therefore, the effect of surfactant heterogeneity on the interfacial structure and dynamics remains poorly understood. Here, we use ultrafast two-dimensional infrared spectroscopy and molecular dynamics simulations to characterize sub-picosecond solvation dynamics as a function of the surfactant composition in ∼120 nm water-in-oil reverse micelles. We probe the ester carbonyl vibrations of nonionic sorbitan surfactants, which are located precisely at the interface between the polar and nonpolar regions, and as such, report on the interfacial water dynamics. We show a 7% increase in hydrogen bond populations together with a 37% slowdown of interfacial hydrogen bond dynamics in heterogeneous mixtures containing hundreds of species, compared to more uniform compositions. Simulations, which are in semiquantitative agreement with experiments, indicate that structural diversity leads to decreased packing efficiency, which in turn drives water further into the otherwise hydrophobic region. Interestingly, this increase in hydration is accompanied by a slowdown of dynamics, indicating that water molecules solvating surfactants are conformationally constrained. These studies demonstrate that the composition and heterogeneity are key factors in determining interfacial properties.

Microemulsions: The Renaissance of Ferrite Nanoparticle Synthesis

Ferrite nanoparticles (NPs) are of special interest for a wide range of applications. Microemulsions represent the Renaissance of ferrite NP preparation offering a series of advantages with respect to other methods due the possibility to confine reactions into nanosized reactors. They allow the preparation in mild synthesis conditions of a wide variety of nanostructured ferrites with controlled composition, particle size and shape. This review wants to give a comprehensive overview of the microemulsion performance in the ferrite NP synthesis. Firstly, a general section on microemulsion properties is presented. The basics of NP formation mechanism, with a first-rate emphasis in the influence of microemulsion properties and dynamics on the control of NP size and shape, are addressed. A summary of the synthesis procedure evolution by both direct and reverse microemulsions over a selection of ferrite NPs is also provided in the review. Finally, the perspectives on microemulsion systems for ferrite NP preparation are quickly revised.

Selected physicochemical properties of water-fuel microemulsion as an alternative fuel for diesel engine

The paper focuses on the assessment of selected physicochemical properties of microemulsion containing 5% by mass (m/m) of surface active compounds (SAC), i.e. Span20 and Crilet4 as well as 10 % (m/m) of distilled water dispersed in diesel fuel (DF). In particular temperature dependent properties such as: flash point (FP) and cold filter plugging point (CFPP) as well as lubricity, friction coefficient, corrosiveness and kinematic viscosity of tested fuels were examined. It was found that the tested surfactants and water added to DF increase microemulsion FP by 13 ºC. For this reason, it can be stated that tested microemulsion is safer than typical DF. On the other hand it was found that the CFPP of the tested microemulsion is also adequately higher. It means less usefulness of such fuel during winter periods. Based on the research results it can be stated that addition of tested surfactants slightly worsens the lubricity of DF. However, the same surfactants in the presence of dispersed water reduce the friction in the tribological node and improve the lubricity of the tested microemulsion. Research showed that tested microemulsion system is not corrosive as well as its kinematic viscosity meet requirements of EN590 standard. Based on all these findings, microemulsion is considered as safe and such fuel can be recommended for engine tests without the risk of its damage.

Nanoparticle Formation in Stable Microemulsions for Enhanced Oil Recovery Application

Magnetic iron oxide and titanium dioxide nanoparticles (NPs) have been synthesized inside stable oil-in-water microemulsions in harsh environment of high temperature-high salinity (HT-HS). Screening of anionic−nonionic mixture of commercial surfactants was carried out to identify the appropriate compositions for the production of stable microemulsions in harsh environment. The effects of salinity and NPs formation on interfacial tension and rheological properties of microemulsions were evaluated and compared with other studies. It was found that oil-inwater microemulsions exhibit a non-Newtonian behavior in the absence of NPs, while the surfactant solutions show Newtonian behavior. The shear-thinning characteristic of microemulsions was improved and the interfacial tension between microemulsions and oil phase was increased after generation of NPs. A set of flooding experiments were accomplished using a microfluidic device to assess the efficiency of enhanced oil recovery on the pore scale in the absence and presence of NPs. The flooding tests confirmed the improvement of oil recovery efficiency after the formation of NPs inside the microemulsions. The oil displacement of API flooding was equal to 69.8% and the maximum oil displacement of 76.9% was observed after the injection of microemulsion containing iron oxide NPs.

DoE-based development, physicochemical characterization, and pharmacological evaluation of a topical hydrogel containing betamethasone dipropionate microemulsion

This study was performed to achieve two primary goals: First, a microemulsion containing betamethasone dipropionate was optimized using the quality by design approach. Second, a hydrogel-containing microemulsion was developed using cellulose derivatives, and its anti-inflammatory and skin irritation effects were evaluated. Face-centered central composite design was used to investigate the impacts of two independent variables (oleic acid and ratio of surfactant to cosolvent, S/CoS) on three dependent variables (skin deposition, flux of BMD, and microemulsion droplet size). The microemulsion including oleic acid at a low level (coded with -1) and S/CoS at a high level (coded with +1) was considered optimal since it was the most effective in terms of skin deposition and flux of BMD. Different cellulose derivatives (HPMC E6, HEC, NaCMC, and CMC) were screened to prepare a hydrogel-containing microemulsion based on four properties: flux and skin deposition of BMD, hydration of stratum corneum, and rheological properties of hydrogel-containing microemulsion (ME-hydrogel). The anti-inflammatory effect and flux of BMD from optimal ME-hydrogel with carboxymethyl cellulose as the hydrogel-forming agent were then compared to those of the hydrogel-containing solid lipid nanoparticles (SLN-hydrogel) and nanostructure lipid carriers (NLC-hydrogel). The percentage of edema inhibition declined proportionally with flux of BMD in the following order: ME-hydrogel (44.56 ± 8.08%) > NLC-hydrogel (35.93 ± 7.22%) > SLN-hydrogel (25.68 ± 9.05%).

RSM optimization of oil-in-water microemulsion stabilized by synthesized zwitterionic surfactant and its properties evaluation for application in enhanced oil recovery

Recent advances in formulation and designing of microemulsion with improved viscosity and an ability to reduce interfacial tension, miscibility with oil, have led to their application in enhanced oil recovery (EOR). The physicochemical properties of microemulsion varies widely depending on its composition, stability and temperature. In present study, an investigation has been made to formulate microemulsion using zwitterionic surfactant as amphiphile and mineral oil as oleic phase. The optimization of formulation of microemulsion with desired properties was obtained by response surface methodology (RSM). The accuracy and significance of model developed by RSM was tested by analysis of variance (ANOVA) and the model generated was used to analyse the effect of individual components on microemulsion formulation. The optimized microemulsion obtained using RSM was characterized by particle size and zeta potential analysis. The stability and miscibility tests of microemulsion showed excellent results for applicability in chemical EOR. The viscosity of the microemulsion was found to be around 300mPaS at 10s−1 shear rate, which is highly encouraging for its application in EOR to improve the mobility ratio. The interfacial reduction and wettability alteration properties of microemulsion was also found to be superior to that of surfactant solution. The core flooding experiment showed that the optimized microemulsion was able to recover 26.83% of additional oil as compared to 20.01% of oil recovery by surfactant flooding, over the conventional water flooding.

Molecular dynamics simulation of supercritical CO2 microemulsion with ionic liquid domains: Structures and properties

Abstract Supercritical carbon dioxide microemulsions are great medium to combine two immiscible substances through forming nanoscale polar cores in nonpolar continuous phase with the help of proper surfactants. The properties of microemulsions could be significantly affected by their constituents and structures. In this work, molecular dynamics simulation was implemented to study supercritical carbon dioxide microemulsions containing ionic liquid [bmim][PF6] and water by adding surfactant Ls-36. Results showed that the above components could form spherical aggregates in CO2 bulk phase with [bmim][PF6] and some water as the inner core, surfactant headgroups and water as the intermediate shell, and surfactant tails as the outer shell. The microstructure information about the outer shell was further investigated by defining an angle between the surfactant tail and the normal direction of the aggregate outer surface, which ranged from 78° to 125°. The influence of the ionic liquid content on the size and structure of microemulsions was explored and the best molar ratio between the ionic liquid and surfactant was around 1.25 for getting maximum water solubility.

Preparation, investigation and characterization of microemulsion used in cleaning waste liquid and drilling cuttings

ABSTRACTIn order to cleaning the drilling cutting and treating the waste liquid which were produced in oil and gas field, several kinds of microemulsion with potential applications in the cleaning system for waste liquid were prepared by using diesel oil, water, n-hexyl alcohol, and mixture surfactant. The stability and formation mechanism of optimal microemulsion were characterized by using dynamic light scattering and fluorescence probe technique. Furthermore, the effects of salinity, temperature and pH on the properties of microemulsion were investigated by setting different gradients. The cleaning efficiency was evaluated by contact angle experiment. It can be proposed that the microemulsion is suitable for cleaning the waste liquid.

Effect of tocopherol on the properties of Pluronic F127 microemulsions: Physico-chemical characterization and in vivo toxicity

The development of biodegradable and biocompatible microemulsions to transport and deliver hydrophobic bioactive molecules is a fundamental challenge in pharmacological sciences. In the current work, oil-in-water Pluronic F127-based microemulsions using different fatty acids (sodium decanoate, SD, and sodium caprylate, SC) as co-surfactants were characterized as potential nanocarriers to solubilize and transport tocopherol (TOC) at Ow = [ethyl butyrate] / [Pluronic] = 1 and oil nanodroplet mass fraction (MFD) between 0.01 and 0.08 using dynamic light scattering (DLS) and dynamic surface tension (DST) techniques. DLS data showed that as the fatty acid chain length increased from sodium decanoate (SD) to sodium caprylate (SC), the nanodroplet size also did whereas the opposite behaviour was found as the MFD increased. DST data revealed that surface tension reached much faster the thermodynamic equilibrium for SD-stabilized compared to SC-stabilized Pluronic F127-based microemulsions. These were able to load important amounts of TOC with a high encapsulation efficiency. The release profile of the cargo compound from the microemulsions was sustained along time. In addition,2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity of TOC was examined, and results reported as the half maximal inhibitory concentration (IC50) values. Finally, to evaluate the potential cytotoxicity of the obtained TOC-loaded microemulsions preliminary in vivo experiments were performed. Microemulsions were parenterally administered in healthy rats and blood was collected to analyze serum levels of alanine aminotransferase (ALT), serum aspartate aminotransferase (AST), serum creatinine, serum blood urea nitrogen (BUN) and lactate dehydrogenase (LDH). Experimental data indicated a significant decrease in serum BUN and creatinine levels while other parameters remained unchanged. Also, the drug-loaded microemulsions-treated group showed symptoms of lethargy, nausea, and reduced food intake following injection, but no mortality was reported.

Effects of Continuous Phase and Crosslinking Agent on the Rheological Behaviors and Properties of Cationic Poly(urethane-acrylate) Emulsifier-Free Microemulsions.

Cationic poly(urethane-acrylate) emulsifier-free microemulsions are prepared by seeded emulsion polymerization (SPUA) or in-situ emulsion polymerization (IPUA) with (a) or without (b) crosslinking agent hydroxyethyl acrylate (HEA). Furthermore, no surfactant is introduced into the reaction system. The effect of continuous phase and HEA on the rheological behavior and properties of microemulsions are studied. The results show that IPUA using vinylmonomers as the continuous phase and with HEA (IPUAMB-b) has the highest ζ value, lowest coagulation ratio, smallest particle size of 48 nm and apparent core-shell structures. Rheological research has concluded that the zero-shear viscosity of IPUAB-b and IPUAM-b emulsion is 6.03×102 and 7.89 Pa·s, respectively, and presents pseudoplastic behavior. However, IPUAMB-b and SPUA-b display Newtonian behavior with η0 of 0.136 Pa·s and 0.0823 Pa·s, respectively. PUA emulsions display similar rheological behavior when NMP is replaced by the mixture of MMA and BA.

New Surfactants and Cosolvents Increase Oil Recovery and Reduce Cost

Summary Scientific understanding of how the molecular structures of surfactants and cosolvents affect microemulsion properties greatly speeds up the process of arriving at optimal chemical formulations for enhanced recovery of a specific crude oil. With the main emphasis on reducing the chemical cost of the formulations, novel surfactants and cosolvents have been developed and shown to have superior performance. We have synthesized and tested surfactants with different hydrophobe sizes and structures varying from ultrashort to large to satisfy a variety of crude-oil requirements over a wide range of reservoir conditions. The cosolvents and surfactants with ultrashort hydrophobes offer advantages such as short equilibration time for the microemulsion formation and lower microemulsion viscosity. Chemical formulations developed using these chemicals have shown excellent performance with very low cosolvent and surfactant retention in cores. Low retention means less chemicals can be used to recover each barrel of oil from the reservoir. These chemicals can be made commercially at low cost. Through use of these new developments, the chemical cost per barrel of oil is low enough to be economically viable, even at low crude-oil prices.

The Influence of Di-(2-Ethylhexyl)Phosphoric Acid on the Properties of Microemulsion in the Sodium Di-(2-Ethylhexyl)Phosphate–Di-(2-ethylhexyl)Phosphoric Acid–Decane–Water System

It has been shown that the presence of small amounts of di-(2-ethylhexyl)phosphoric acid (below 6 mol % in the mixture of surfactants) in a sodium di-(2-ethylhexyl)phosphate–di-(2-ethylhexyl)phosphoric acid–decane–water system widens the region of microemulsion existence with respect water and decreases the slope of the dependence of hydrodynamic droplet diameter of on water-to-sodium di-(2-ethylhexyl) phosphate molar ratio. At di-(2-ethylhexyl)phosphoric acid concentrations in its mixture with sodium di-(2-ethylhexyl)phosphate higher than 6 mol %, the fraction of water bound with ions in microemulsion droplets decreases, the region of microemulsion existence narrows, specific conductance decreases, and the slope of the dependence of the hydrodynamic droplet diameter of on the water-to-sodium di-(2-ethylhexyl) phosphate molar ration increases.

Structure of micelles and micro-emulsions probed through the molecular reorientation of water

We study the structural properties of dodecyltrimethylammonium bromide (DTAB) micelles and micro-emulsions by probing the molecular reorientation of water with polarization-resolved infrared pump-probe spectroscopy. For all systems studied, we observe that a fraction of water reorients on a much slower timescale than bulk water. This slow water fraction increases sublinear with increasing DTAB concentration, indicating an increase of the micelle size and enhanced micelle aggregation with concentration. We observe that the addition of oil to the micelle solutions, leading to the formation of a micro-emulsion, does not lead to a significant change of the fraction of slow water, showing that the added oil molecules are well solvated within the core of the micelles, and thus completely shielded from water.

Effect of Increasing Concentrations of Tween 80 and Sorbitol as Surfactants and Cosurfactans Against the Physical Stability Properties of Palm Oil Microemulsion

Faculty of Pharmacy and Science, University of Muhammadiyah Prof. Dr. Hamka, Jakarta, Indonesia Palm oil is one of the fatty oil can used as the oil phase in the microemulsion system. The purpose of this research was to identify the effect of increasing concentration of combination of surfactant and cosurfactant on the physical stability of palm oil microemulsion. This oil was formulated into microemulsion system by increas ing concentration of combination of tween 80 and sorbitol (1:1) in various concentrations, which were 54%, 56%, 58% and 60% as surfactant and cosurfactant component. The evaluation included organoleptic, viscosity test, pH, density, surface tension and particle size and zeta potential test. The pH showed in the range 5.8 to 6.4. Viscosity value obtained between 637.47 to 808.20 Cps. Density measurement were between 1.1123 to 1.1235 g/ml. The results of surface tension obtained between 39.76 to 43.07 dynes/cm. The results of particle size measurement results obtained from 21.27 to 23.97 nm and the zeta potential between −10.28 to −18.03. It can be concluded that the increasing of concentration of surfactant and cosurfactant can improve physical stability of the microemulsion.

Controlling the composition, phase volume, and viscosity of microemulsions with cosolvent

Optimizing macroscopic properties of microemulsions (volume, composition, and viscosity) is tedious and often involves the use of an alcohol. We show that this optimization is possible when the alcohol acts as cosolvent (rather than a cosurfactant) to partition between the interface and bulk phases(s). Herein presented a phase behavior study of water, crude oil, tridecyl alcohol propoxy sulfate (C13-13PO-SO4), internal olefin sulfonate (C20-24IOS), and ethoxylated phenol (phenol-2EO) mixtures, rationalized by pseudophase theory and pseudoternary phase diagram. The detailed phase behavior study involved varying the surfactant concentration, cosolvent concentration, brine salinity, and oil content. High-performance liquid chromatography (HPLC) was used to determine the interfacial composition and steady and dynamic rheology to characterize the bicontinuous middle-phase samples. Measurements confirmed that phenol-2EO acted as cosolvent. A systematic shift of phase type is observed by increasing the cosolvent-to-surfactant content in the initial water/surfactant solution. Furthermore, it was observed that the interfacial ratio of cosolvent to surfactant controls the microemulsion composition, viscosity, and volume. This ratio is highly tunable, but when too high, a distortion of the middle phase is observed. The experimental results provide a methodology to tailor the composition of amphiphile mixture for optimizing microemulsion properties.