Water In Microemulsions Research Articles

Lipid–water partition coefficients and correlations with uptakes by algae of organic compounds

In view of the scarcity of the lipid–water partition coefficients (Ktw) for organic compounds, the logKtw values for many environmental contaminants were measured using ultra-pure triolein as the model lipid. Classes of compounds studied include alkyl benzenes, halogenated benzenes, short-chain chlorinated hydrocarbons, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and organochlorine pesticides. In addition to logKtw determination, the uptakes of these compounds from water by a dry algal species were measured to evaluate the lipid effect on the algal uptake. The measured logKtw are closely related to their respective logKow (octanol–water), with logKow=1.9 to 6.5. A significant difference is observed between the present and early measured logKtw for compounds with logKow>∼5, which is attributed to the presence and absence of a triolein microemulsion in water affecting the solute partitioning. The observed lipid-normalized algae–water distribution coefficients (logKaw/lipid) are virtually identical to the respective logKtw values, which manifests the dominant lipid-partition effect of the compounds with algae.

Tween-80–n-Butanol–Diesel–Water Microemulsion System—A Class of Alternative Diesel Fuel

Tween-80–n–butanol–diesel–water microemulsion systems with various surfactant:cosurfactant (S:C) ratio have been reported as a class of alternative diesel fuel from their phase behavior, clouding phenomena, conductivity, turbidity, and inflammation studies. Temperature induced clouding of microemulsion containing 2% brine at an S:C ratio of 1:1 from a suitable turbid zone has been examined to see the stability of the diesel–water microemulsion systems. Regression models have been proposed to understand the impact of various components of the microemulsion on their cloud point (CP) values. Conductivity of the microemulsions at various S:C ratio increases with the volume of brine having two cut points depicting the presence of three microheterogenous phases within the system, whereas turbidity shows a linear increase. Dye-probed investigation of water-rich and oil-rich zones of the microemulsions indicates the involvement of a dynamic mass transfer process within the various zones. The intensities of flames produced during burning of the microemulsions with various O:E:W weight percentages selected from the isotropic regions of the phase diagrams have been estimated using MATLAB image processing method and the impacts of various components on the fuel use of the microemulsions have been analyzed.

Emulsification Based Liquid Microextraction Prior to Flame Atomic Absorption Spectrometry for Sensitive Determination of Copper in Water Samples

In this study emulsification based liquid microextraction (EBLME) was developed for preconcentration of Cu(II) using a redesigned dispersive liquid - liquid microextraction (DLLME). The procedure is based on an organic extraction solvent and aqueous solution of surfactant system where a mixture contains appropriate amounts of the extraction solvent (25.6 µg mL-1 dithizone chloroformic solution) and aqueous solution of sodium dodecyl sulfate (SDS) as a disperser. Immediately after the injection, a cloudy media is formed containing oil in water microemulsions; into which the analyte ions could be extracted. After centrifugation, the copper is determined in the enriched phase by flame atomic absorption spectrometer. Some factors influencing the extraction efficiency of copper ion determination were studied and optimized. Under the optimized conditions, the relative standard deviation (RSD) for seven repeated determinations, at a concentration of 0.2 µg mL-1 was obtained to be 3.9 %. The limit of detection and enrichment factor were 0.32 ng mL-1 (S/N = 3) and 147, respectively. A comparison between the employed method and dispersive liquid–liquid microextraction indicates that emulsification based liquid microextraction (EBLME) has simplicity, rapidity, reproducibility, and possesses lower limit of detection and higher enrichment factor for determination of copper ion in natural waters. Keywords: Emulsification based liquid microextraction, Copper, Water analysis, flame atomic absorption spectrometry, Surfactant, Preconcentration.

Diffusion properties of liquid crystal-based microemulsions

Microscopic diffusion processes in thermotropic 5CB liquid crystals (LC) with imbedded surfactant-stabilized water microemulsions are studied using pulsed field gradient nuclear magnetic resonance (PFG NMR). The experiments are performed in a temperature range around the isotropic-nematic transition temperature of the LC. The temperature dependence of the diffusivities of the liquid crystal and surfactant molecules remains almost unchanged in the whole temperature range studied. With varying water content, the diffusivities of the surfactant molecules are found to be almost invariable, indicating that the surfactant diffusivities remain essentially unaffected by whether a microemulsion is formed or the surfactant molecules diffuse as individual species. At the same time, the formation of the microemulsion is found to be crucial for the macroscopic separation of the mixture into LC- and surfactant-rich phases.

Antimicrobial Mechanism Analysis of an Oil in Water Microemulsion by DNA Microarray-Mediated Transcriptional Profiling ofEscherichia Coli

The DNA microarray was employed in this study to investigate the gene expression profiles of Escherichia coli treated by oil in water (o/w) microemulsion in order to better understand the antimicrobial mechanism of the microemulsion as a promising food-grade antimicrobial system. Among 5,440 open reading frames of E. coli, a total of 634 and 501 were highly induced and repressed, respectively. According to the annotation and analysis in the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, it was found that the differently expressed genes were mainly involved in the biosynthesis of cell wall components and membranes, phosphate-related metabolism and some other biosynthetic pathways, suggesting that the main antibacterial mechanisms of the o/w microemulsion were the attacks to the cell surface structure, especially the cell wall, and its influences on the metabolism of phosphate of the E. coli cells through phosphate absorption inhibition. Practical Applications In the panorama of the increasing need to search for novel strategies in order to prevent foodborne outbreaks, microemulsion systems have been of great interest to researchers for their broad antimicrobial properties. In our group, a series of food-grade or pharmaceutical microemulsion systems based on glycerol monolaurate have been established for antimicrobial applications. It was found that the prepared microemulsions possessed excellent broad-spectrum antimicrobial activities due to the disruption and dysfunction of biological membranes and cell walls, as suggested by the transmission electron microscopy observations and membrane permeability experiments. The antimicrobial mechanisms analysis of the microemulsion mediated by DNA microarray in this work will be of great importance in exploring the structure–activity relationship of the o/w microemulsion at molecular biological levels in future work, in order to provide a guideline in designing food-grade antimicrobial microemulsions.

The Preparation and Characterization of ZnS/PMMA Nanocomposites

IIB-VIA group of semiconductor ZnS nanoparticles, which were coated with polymethylmethacrylate (PMMA), are prepared in n-heptane/sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/water microemulsions. Through the reaction of Zn(Ac)2 with the S2– ions released slowly from Na2S, the ZnS nanoparticles were synthesized, then the monomer MMA was dropped into the mixed microemulsion system. After polymerization, the composite was successfully obtained. The initial dosages of all reactants were determined by academic analysis. The products were characterized by UV-vis absorption spectroscopy, X-ray powder diffraction (XRD), and transmission electron microscopy (TEM). The UV/Vis absorption indicates the quantum confinement effect of ZnS nanoparticles. The structure of the composite is characterized by XRD, which reveals that cubic ZnS particles are formed. The TEM image of the sample shows that the diameter of ZnS nanoparticles is approximately 20 nm.

Synthesis and modeling of calcium alginate nanoparticles in quaternary water-in-oil microemulsions

Calcium alginate nanoparticles were prepared using the water-in-oil microemulsion route. Sodium alginate and CaCl2 were solubilised in the aqueous phase of two microemulsions, and their mixing induced the crosslinking of the alginate polymer by the calcium ions. The microemulsions were based on the nonionic ethoxylated surfactant Brij30 and the nonionic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock-copolymer L64. Dynamic light scattering analysis revealed that the microemulsion droplet size was not affected by the species in the aqueous phase and that the alginate polymer was strongly confined in the microemulsion water pool. Atomic force microscopy of the collected alginate nanoparticles indicated a polydisperse population with an average size of 54nm and hinted at an active template role of the microemulsion droplets. A detailed description of the conformation adopted by the alginate polymer in the water droplet in the presence of mono- and divalent counterions was provided by Monte Carlo simulations. The binding of both counterions was nonspecific, with the chain configuration allowing the carboxylic, hydroxylic, and ether groups to coordinate the small ions. Addition of divalent counterions did not modify the radial extension of the alginate chain, yet it mediated the transient bridging between strands.

Phase Behavior of Bicontinuous and Water/Diesel Fuel Microemulsions Using Nonionic Surfactants Combined with Hydrophilic Alcohol Ethoxylates

Bicontinuous and water-in-diesel microemulsions were formulated using single nonionic alkyl poly glycol ethers combined with hydrophilic alcohol ethoxylates. The phase behavior at temperatures ranging from 0°C to 50°C was investigated. Visual inspection as well as cross-polarizers were used to detect anisotropy. The fish phase diagrams were determined. The presence of the hydrophilic alcohol ethoxylates was necessary to initiate both types of microemulsions. Increasing the hydrophobic chain length of the surfactant led to a wider range of temperature stability at lower surfactant concentration. Meanwhile, increasing the ethylene oxide units in the headgroup by two units led to a phase diagram that is dominated by lyotropic liquid crystal. The formulated water in diesel microemulsions were tested experimentally in a 4-cylinder diesel engine. From this it is observed that the emissions of NOx, soot, and CO2 were reduced substantially compared to neat diesel, while for the CO the reduction occurs just at low load.

Shape Transitions in Supercritical CO2 Microemulsions Induced by Hydrotropes

The ability to induce morphological transitions in water-in-oil (w/o) and water-in-CO2 (w/c) microemulsions stabilized by a trichain anionic surfactant 1,4-bis(neopentyloxy)-3-(neopentyloxycarbonyl)-1,4-dioxobutane-2-sulfonate (TC14) with simple hydrotrope additives has been investigated. High-pressure small-angle neutron scattering (SANS) has revealed the addition of a small mole fraction of hydrotrope can yield a significant elongation in the microemulsion water droplets. For w/o systems, the degree of droplet growth was shown to be dependent on the water content, the hydrotrope mole fraction, and chemical structure, whereas for w/c microemulsions a similar, but less significant, effect was seen. The expected CO2 viscosity increase from such systems has been calculated and compared to related literature using fluorocarbon chain surfactants. This represents the first report of hydrotrope-induced morphology changes in w/c microemulsions and is a significant step forward toward the formation of hydrocarbon worm-like micellar assemblies in this industrially relevant solvent.

Comparative Study of Injection Systems in Vapor Phase in the Remediation of Soils Contaminated by Diesel

Gasoline and diesel leaks in underground storage tanks contaminate soils with petroleum hydrocarbons. Various techniques using surfactants have been proposed to remedy this type of contamination. This study presents the application of different systems containing surfactants in vapor phase. It compares the removal efficiencies of diesel contaminated soils using vapor injection systems: surfactant water solutions, micro-emulsions, and nano-emulsions. The surfactant used in the experiments was ethoxylated alcohol UNTL-90 in aqueous solution, in nano-emulsion, and micro-emulsion systems. Among the systems investigated, the nano-emulsion showed the highest removal efficiency (88%), being environmentally friendly and technically feasible with a system that has a lower content of active matter.

A novel approach for preparation of CL-20 nanoparticles by microemulsion method

2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) as one of the high energy cage nitramines has been used in various propellants and explosive formulations. The performance of energetic materials depends on its particle size and shape. Therefore, in this research, microemulsion method has been applied for the preparation of CL-20 nanoparticles via oil in water (O/W) microemulsions. The optimized formulation contains water 45%, n-butyl acetate 20.5%, sodium dodecyl sulfate (SDS, as anionic surfactant) 6.5% and 2-propanol (as co-surfactant) 26.5%. CL-20 nanoparticles that were obtained by microemulsion method are spherical with an average diameter of 25nm, based on TEM image. CL-20 nanoparticles were also characterized by SEM image analysis, FTIR spectroscopy and TG method.

Fragrance solubilization in temperature insensitive aqueous microemulsions based on synergistic mixtures of nonionic and anionic surfactants

Well-defined tetraethylene glycol monooctylether (C8E4) and its commercial polydispersed counterpart (Dehydol® O4) were used to solubilize fragrances. Addition of small amounts (≤1wt.%) of the ionic surfactants, sodium dodecylsulfate (SDS) or sodium lauryl ether sulfate (SLES), permits the formulation of temperature insensitive fragrance in water microemulsions. The investigation of the pseudo-ternary surfactants/β-pinene/water systems allows the determination of the optimum temperature T* as well as the assessment of the efficiency of the surfactant mixtures to solubilize β-pinene. A mixture of Dehydol O4 and SDS (9/1wt.%) can solubilize 6.5wt.% of β-pinene in water within the temperature range of 25–80°C. This synergistic formulation was also applied to the solubilization of p-cymene, the essential oils pinus pinaster and pinus sylvestris and a true fragrant mixture composed of 9 terpenes and terpenoids in dipropylene glycol.

Reverse micelle synthesis of oxide nanopowders: Mechanisms of precipitate formation and agglomeration effects

We present an analysis of reverse micelle stability in four model systems. The first two systems, composed of unstable microemulsions of isooctane, water, and Na-AOT with additions of either iron sulfate or yttrium nitrate, were used for the synthesis of iron oxide or yttrium oxide powders. These oxide powders were of nanocrystalline character, but with some level of agglomeration that was dependent on calcination temperature and cleaning procedures. Results show that even though the reverse micellar solutions were unstable, nanocrystalline powders with very low levels of agglomeration could be obtained. This effect can be attributed to the protective action of the surfactant on the surfaces of the powders that prevents neck formation until after all the surfactant has volatilized. A striking feature of the IR spectra collected on the iron oxide powders is the absence of peaks in the ∼1715cm−1 to 1750cm−1 region, where absorption due to the symmetric CO (carbonyl) stretching occurs. The lack of such peaks strongly suggests the carbonyl group is no longer free, but is actively participating in the surfactant-precipitate interaction. The final two microemulsion systems, containing CTAB as the surfactant, showed that loss of control of the reverse micelle synthesis process can easily occur when the amount of salt in the water domains exceeds a critical concentration. Both model systems eventually resulted in agglomerated powders of broad size distributions or particles that were large compared to the sizes of the reverse micelles, consistent with the notion that the microemulsions were not stable and the powders were precipitated in an uncontrolled fashion. This has implications for the synthesis of nanopowders by reverse micelle synthesis and provides a benchmark for process control if powders of the highest quality are desired.

Improved thermal stability of lipase in W/O microemulsion by temperature-sensitive polymers

Lipase is active at the water–oil interface and thus very useful for many applications in non-aqueous media. However, the use of lipase is often limited due to the heat inactivation which is mainly caused by the irreversible aggregation among lipase molecules. The temperature-sensitive polymers can spontaneously form complexes with lipases at higher temperature in the confined spaces of the water in oil microemulsion. With cooling, lipases are released from the complexes and refold into the native state. In this way, the thermal stability of lipase in a microemulsion is effectively improved, and so is the stability of lipase at ambient temperature. Apart from proving the effectiveness and generality of this method, the temperature-sensitive polymers/lipase microemulsion represents a simple and efficient system which could be used in practical applications, since lipase retains the interfacial activity in this system. Moreover, the influences of some factors on the improvement are discussed and the mechanism of this method is suggested after exploring the process by dynamic light scattering and fluorescence measurements.

Kinetics and mechanism of lipase catalyzed monoacylglycerols synthesis

Abstract Monoacylglycerols are increasingly used in several industrial applications as effective and cheap emulsifiers. In the present work monostearin synthesis has been studied, using lipase as a biocatalyst of the esterification reaction of stearic acid with (R,S)-1,2-O-iso-propylidene glycerol (solketal). The lipase from Candida antarctica (CaL B) was immobilized in AOT/isooctane water in oil microemulsions. Optimization of the reaction conditions have shown that the highest production (80% in 30 min) could be achieved at 40 °C, in microemulsions with relatively low water content (wo = 8). Kinetic studies have shown that the esterification reaction of stearic acid with solketal catalyzed by CaL B occurs via the ordered bi–bi mechanism, in which inhibition by the acid was identified. Moreover, at high fixed solketal concentrations a negative cooperativity is pronounced, which means that binding of the alcohol lowers the affinity of the enzyme for binding of the acid. Values of all kinetic parameters have been determined.

Preparation of submicrometer monodispersed magnetic silica particles using a novel water in oil microemulsion: properties and application for enzyme immobilization

The synthesis of monodispersed magnetic silica nanoparticles (MSN) is described using a water-in-oil reverse microemulsion system that does not require the use of co-surfactants. Sodium silicate, Tween 20 as a neutral surfactant and 1-butanol as the organic phase were used. There are several advantages of the proposed method including a saturation magnetization value of 10 emu/g for the particles obtained, uniformity of size and that they are easily functionalized to bind urease covalently. Moreover, the intra-day, inter-day and long-term stability results confirm that the procedure was successful and the enzyme-linked MSNs were stable over repeated uses and storage retaining more than 75% activity after 4 months.

Nanostructures in Water-in-CO2 Microemulsions Stabilized by Double-Chain Fluorocarbon Solubilizers

High-pressure small-angle neutron scattering (HP-SANS) studies were conducted to investigate nanostructures and interfacial properties of water-in-supercritical CO2 (W/CO2) microemulsions with double-fluorocarbon-tail anionic surfactants, having different fluorocarbon chain lengths and linking groups (glutarate or succinate). At constant pressure and temperature, the microemulsion aqueous cores were found to swell with an increase in water-to-surfactant ratio, W0, until their solubilizing capacities were reached. Surfactants with fluorocarbon chain lengths of n = 4, 6, and 8 formed spherical reversed micelles in supercritical CO2 even at W0 over the solubilizing powers as determined by phase behavior studies, suggesting formation of Winsor-IV W/CO2 microemulsions and then Winsor-II W/CO2 microemulsions. On the other hand, a short C2 chain fluorocarbon surfactant analogue displayed a transition from Winsor-IV microemulsions to lamellar liquid crystals at W0 = 25. Critical packing parameters and aggregation numbers were calculated by using area per headgroup, shell thickness, the core/shell radii determined from SANS data analysis: these parameters were used to help understand differences in aggregation behavior and solubilizing power in CO2. Increasing the microemulsion water loading led the critical packing parameter to decrease to ~1.3 and the aggregation number to increase to >90. Although these parameters were comparable between glutarate and succinate surfactants with the same fluorocarbon chain, decreasing the fluorocarbon chain length n reduced the critical packing parameter. At the same time, reducing chain length to 2 reduced negative interfacial curvature, favoring planar structures, as demonstrated by generation of lamellar liquid crystal phases.

Microstructural Investigation Of Lipid Solubilized Microemulsions Using Laser Light Scattering

Solubilization of solid lipids in oil-in-water microemulsion is an important step in the preparation of lipid nanoparticles. Oil in water microemulsion has been prepared using Tween-80 (T-80) as a surfactant and isopropyl myristate (IPM) as an oil phase with a view to utilize them for the preparation of Solid Lipid Nanoparticles (SLN). The microstructure of the microemulsions were evaluated using laser light scattering studies. From light scattering studies, it was observed that the intensity of scattered light increases on increasing the concentration of IPM at a fixed concentration of T-80 (15%), reflecting an increase in the size of the micelles. Dynamic light scattering studies show that the hydrodynamic diameter of the micelles increases on increasing the concentration of IPM. Phospholipon® 90 G (lipid) solubilized microemulsions were prepared using 1:1 w/w mixture of lipid and IPM as the oil phase. DLS studies suggest that addition of lipid did not alter the size of microemulsion droplets significantly.

Transdermal delivery of betahistine hydrochloride using microemulsions: Physical characterization, biophysical assessment, confocal imaging and permeation studies

Transdermal delivery of betahistine hydrochloride encapsulated in various ethyl oleate, Capryol 90®, Transcutol® and water microemulsion formulations was studied. Two different kinds of phase diagrams were constructed for the investigated microemulsion system. Pseudoplastic flow that is preferable for skin delivery was recorded for the investigated microemulsions. A balanced and bicontinuous microemulsion formulation was suggested and showed the highest permeation flux (0.50±0.030mgcm−2h−1). The effect of the investigated microemulsions on the skin electrical resistance was used to explain the high permeation fluxes obtained. Confocal laser scanning microscopy was used to confirm the permeation enhancement and to reveal the penetration pathways. The results obtained suggest that the proposed microemulsion system highlighted in the current work can serve as a promising alternative delivery means for betahistine hydrochloride.

Oil-in-water microemulsions based on cationic surfactants with a hydroxyalkyl fragment in the head group

The stable oil-in-water microemulsions with a high water content were formed on the basis of cationic surfactants, including those that contain a hydroxyalkyl fragment in the head group. These systems can bind the water- and oil-soluble reagents into a single aggregate formed by self-assembling components. The size, surface and electrokinetic potentials of aggregates in the surfactant/n-hexane/n-butanol/water microemulsions were determined. Besides, their catalytic effect on the cleavage of carboxylic acid esters was evaluated. The behavior of the system was shown to be determined not only by hydrophobic and electrostatic interactions but also by specific interactions, i.e., hydrogen bonds.