Types Of Microemulsions Research Articles

Design and characterization of selected microemulsions as media for NMR chromatography

NMR chromatography is a promising and superior alternative to NMR spectroscopy for analyzing mixtures since it simultaneously separates the spectra of the compounds and supplies information about their structure. This implies that there is no need for extraction, purification or synthesis of standards, that are expensive, time consuming and usually impractical. The main aim of NMR chromatography is to increase the differences in the diffusivities of different analytes in a mixture, allowing them to be more easily and reliably identified.The selection of surfactants and other components of microemulsions for the best performance as NMR chromatographic media was studied. Attention was focused on the selection of the proper cosolvent in three types of water-dilutable microemulsions: two anionic (deuterated ionic and the previously published fluorinated ionic) and one nonionic (undeuterated Tween-based). The diffusivities of several analytes are compared. The study also examines the effect of dilution and determines the best compositions for the NMR chromatography performance.For the anionic microemulsions, 1-butanol was found to be the most promising cosurfactant in the deuterated system 1-butanol-d10:toluene-d8:SDS-d25 in a 6:3:1 weight-ratio diluted by D2O. This composition, diluted with a 85wt% D2O, formed a microemulsion that was even stable at relatively elevated temperatures (70°C) and can serve as good medium for chromatographic NMR.Another possibility that was studied consists of nonionic-based microemulsions of isopropyl alcohol (IPA) in IPA:toluene:Tween 20 that could also be easily diluted indefinitely with water. IPA was found to be a very efficient cosurfactant at resolving diffusivities of all the components. However, the lack of availability of deuterated Tween makes it impractical for use as an NMR chromatography formulation.

Investigation on Physical Properties and Morphologies of Microemulsions formed with Sodium Dodecyl Benzenesulfonate, Isobutanol, Brine, and Decane, Using Several Experimental Techniques

In the context of chemical enhanced oil recovery (EOR), there is no well-established way to characterize and understand the physical properties and structures of microemulsions composed of crude oil and industrial surfactants due to their complexity. Making a comparison to a well-studied model system is a simple and effective way to investigate the complex microemulsions. The purpose of this study is to provide and complete experimental characteristic data of model-microemulsions as a basis of analysis of the complex system. Types of microemulsions studied in the present work were oil in water (O/W), bicontinuous, and water in oil (W/O). The system was composed of water, sodium dodecyl benzenesulfonate (SDBS), isobutanol, sodium chloride (NaCl), and decane. We performed several experiments at room temperature such as spinning drop method, differential scanning calorimetry (DSC), Karl Fischer titration, Hyamine titration, dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and electron cry...

Laboratory Studies on Fluid-Recovery Enhancement and Mitigation of Phase Trapping by Use of Microemulsion in Gas Sandstone Formations

Summary One of the challenges in slickwater fracturing of gas reservoirs is post-treatment fluid recovery. More than 60% of the injected fluid remains in the critical near-wellbore region and has a significant negative impact on the relative permeability to gas and well productivity. The trapping of water could be caused by capillary forces around the fractured formation. Commonly available surfactants are added to slickwater to reduce surface tension between the treating fluids and gas. The problem with surfactants is that, upon exposure to the formation, they adsorb on the surface of the rock. The addition of microemulsions to the fracturing fluids can result in a reduction in the pressure needed to displace injected fluids and/or condensate from the formations. This alteration of the fracturing fluid effectively reduces the capillary forces in the near-wellbore region, and in the case of fracturing, the fluids that have been trapped in the region surrounding the fracture. This will result in the removal of water and condensate blocks, as well as the mitigation of phase trapping, and therefore, an increase in permeability to gas. This paper examines the effectiveness of microemulsions in the improvement of fluid recovery by use of sandstone cores with permeability greater than 10 md. Compatibility tests were performed for microemulsions to investigate their compatibility with the condensate and stability upon dilution with brine. One microemulsion showed incompatibility and was excluded from further experiments. Coreflood runs that used 20-in. Bandera sandstone cores with permeabilities greater than 10 md showed that the improvement factor in effective gas permeability because of treatment with microemulsions was up to 2.5, depending on the type of microemulsion. Thermal stability tests were performed on microemulsions, and the results showed stability of the microemulsions at high temperatures up to 400°F. A newly developed microemulsion (Nguyen 2013) that was formulated with a blend of anionic and nonionic surfactants, short-chain alcohol, oil, and water was tested and showed a significant reduction in the surface tension between water and nitrogen gas when compared with mutual-solvent and fluoropolymer-surfactant solutions. Among the tested chemicals, ME-V with a contact angle of 63.4° had the lowest capillary pressure, which makes this microemulsion the best treatment fluid among the four chemicals tested for gas-permeability enhancement and cleanup of the fluid in the near-wellbore region. The resulting capillary pressure for the fracture fluid treated with 0.25 wt% of this chemical in 2 wt% KCl is nearly six times lower than that of the untreated fluid with no microemulsion.

A Novel Approach for Rapid Preparation of Monophasic Microemulsions That Facilitates Penetration of Woody Biomass

Microemulsions are a straightforward, efficient, and highly useful complex media for flooding/wetting substrates as a result of their low surface tension and viscosity. Among the four broad general classes of microemulsions (Winsor-I, -II, -III, and -IV), Winsor-IV is by far considered the ideal microemulsion type within the context of woody biomass pretreatment because it is a single phase. In the present study, a never-before reported titration method was developed with the intent of providing a rapid online determination of Winsor-IV type microemulsion formulations under fixed surfactant concentrations for expressly treating woody biomass. A total of 108 surfactant-oil–water formulations based on a sodium dodecylsulfate/pentanol/water/sodium chloride/dodecane system were investigated for their phase behavior, 54 of which yielded Winsor-IV type microemulsions. The ability of the selected microemulsions to affect the crystallinity of cellulose was studied by X-ray diffraction as was the synergetic effect...

Microemulsion-based antifungal gel of luliconazole for dermatophyte infections: formulation, characterization and efficacy studies

Luliconazole (LZ), a poorly water soluble synthetic imidazole derivative is used in the treatment of fungal infections of skin. Hence, the investigation was aimed at formulating microemulsion based gels (MBGs) for solubilization of LZ as well as its better penetration for efficacious anti-fungal treatment. The solubility of LZ in various oils was investigated. Out of tried oils, olive oil exhibited highest solubility. Suitable combination of surfactants and co-surfactants were screened for selected oil to yield O/W type microemulsion. The Pseudoternary phase diagrams were developed to determine microemulsion existence area. The developed microemulsion was evaluated for particle size analysis, isotropicity, pH, drug content and rheology. Drug loaded microemulsion was slowly added to the viscous solution of 1 % Carbomer 934 under magnetic stirring to prepare MBG. The prepared MBG were evaluated in terms of their droplet size, spreadability, stability, in vitro permeation studies, and rheological properties. The phase study revealed that the maximum proportion of oil was incorporated in microemulsion systems when the surfactant-to-cosurfactant ratio was 3:1. The microemulsion was optimized with its components of Olive oil as oil, Capmul MCM as a surfactant and iso propyl alcohol as a cosurfactant. The globule size of the optimized batch was 32.59 nm. The MBG was non-irritant indicating their safety and was active against C. albicans indicating its efficacy. Short term stability study performed as per ICH guideline exhibited stable characteristic of developed formulation. Therefore, MBG of LZ is an efficacious treatment for fungal infections.

PEPTIDE SURFACTANT FOR EOR APPLICATION

Motivated by recent advances on the peptides surfactants that capable of forming emulsion stabilization by lowering the interfacial tension, an extensive set of tests were carried out to further investigate the applicability of peptide molecules for enhanced oil recovery application. A designed peptide surfactant using protein biotechnology approach was laboratory tested at three samples representing the different oil characteristics, water formation, and reservoir rock. The best performance of peptide surfactant obtained is of sample A. Peptide surfactant is able to form microemulsion Type III at pH 11. It can lower the interfacial tension value until the range of 10-2 dyne/cm at 25°C, even though itsn’t reached the desired target yet which is 10-3 dyne/cm or even less. It can also change rock wettability from water wet into strong water wet. Sample A has relatively short hydrocarbon chain compared to samples B and C, it is classifi ed as intermediate oil, medium salinity for water formation, and rock mineral is dominated with quartz without gypsum that is very harmful to the fuction of surfactant. The developed peptide surfactant hasn’t been stable at high temperature yet. When tested at 70°C, the interfacial tension value increase to around 10-1 dyne/cm. Displacement effi ciency using oil sample A is less than 1%. Based on these results, the next peptide surfactant design will be focused on resistance capability improvement to temperature and peptide amino acid structure position to produce the better result of surfactant. The performance test results of peptide surfactant presented in this paper is valuable in designing specifi c peptide surfactant for certain oil fi eld.

Investigation of microemulsion microstructure and its impact on skin delivery of flufenamic acid

Microemulsions are well known penetration enhancing delivery systems. Several properties are described that influence the transdermal delivery of active components. Therefore, this study aimed to characterize fluorosurfactant-based microemulsions and to assess the impact of formulation variables on the transdermal delivery of incorporated flufenamic acid. The microemulsion systems prepared in this study consisted of bistilled water, oleic acid, isopropanol as co-solvent, flufenamic acid as active ingredient and either HexaforTM670 (Hex) or Chemguard S-550-100 (Sin) as fluorosurfactant. Characterization was performed by a combination of techniques including electrical conductivity measurements, small-angle X-ray scattering (SAXS) and nuclear magnetic resonance (NMR) self-diffusion experiments. In vitro skin permeation experiments were performed with each prepared microemulsion using Franz type diffusion cells to correlate their present microstructure with their drug delivery to skin. Electrical conductivity increased with added water content. Consequently, the absence of a conductivity maximum as well as the NMR and SAXS data rather suggest O/W type microemulsions with spherical or rod-like microstructures. Skin permeation data revealed enhanced diffusion for Hex- and Sin-microemulsions if the shape of the structures was rather elongated than spherical implying that the shape of droplets had an essential impact on the skin permeation of flufenamic acid.

Facile electrochemical synthesis, using microemulsions with ionic liquid, of highly mesoporous CoPt nanorods with enhanced electrocatalytic performance for clean energy

We have established a facile and generalizable electrochemical synthesis of metallic mesoporous nanorods in the nanochannels of commercial polycarbonate membranes using microemulsions containing ionic liquids. Herein, we report the preparation of magnetic CoPt nanorods with various meso or nanopores distributions, depending on the microemulsion type (ionic liquid –in-water (IL/W), bicontinuous (β) or water-in-ionic liquid (W/IL)). The synthesized porous nanorods show a much enhanced electrocatalytic activity for methanol oxidation in comparison with compact Pt nanorods (up to 12 times) or Pt/C electrocatalyst (Pt nanoparticles or commercial black platinum). Therefore, the synthesized CoPt mesoporous nanorods could be excellent catalysts in direct methanol fuel cells (DMFC's), as they have high surface areas, large pore volumes and high corrosion stability, and they exhibit promising catalytic properties.

Formulation and characterization of food-grade microemulsions as carriers of natural phenolic antioxidants

Food-grade W/O microemulsions based on lecithin, caprylic/capric triglycerides, isopropyl myristate, alcohols and water were formulated and structurally characterized to be used as potential carriers of natural food antioxidants. Different well-known food antioxidants including gallic acid, p-hydroxybenzoic acid, protocatechuic acid and tyrosol were successfully encapsulated in the aqueous cores of the microemulsions. A pseudo-ternary phase diagram was constructed to determine the extent of the monophasic area that corresponds to an inverted type microemulsion. Apparent hydrodynamic diameter measurements of empty and loaded microemulsions were performed using dynamic light scattering (DLS) and swollen micelles with diameters smaller than 10 nm were detected. Interfacial properties of the microemulsions were studied by electron paramagnetic resonance (EPR) spectroscopy employing the nitroxide spin probe 5-doxylstearic acid (5-DSA). A small increase in spin probe mobility upon addition of the antioxidants was observed; whereas the rigidity of the surfactants was not affected. Cryogenic transmission electron microscopy (Cryo-TEM) indicated the existence of entangled thread-like reversed micelles. Finally, the investigated phenolics were assessed and compared for their radical scavenging activity using an EPR approach based on free radicals. The encapsulated gallic acid showed the highest antioxidant activity (0.93 mM trolox equivalents) as compared to other antioxidants assessed within the frame of this study.

Development and Validation of Micro Emulsion High Performance Liquid Chromatography(MELC) Method for the Determination of Nifedipine in Pharmaceutical Preparation

Microemulsion is a stable, isotropic clear solution consisting of oil based substance, water surfactant and cosurfactant. There are two types of microemulsion which are used as a mobile phase; water in oil (w/o) and oil in water (o/w).Microemulsion has a strong ability to solubilize both hydrophobic and hydrophilic analytes, therefore reducing the pre-treatment of the sample which is needed for the complex sample. Recent reports found that separating the analytes by using microemulsion high performance liquid chromatography can be achieved with superior speed and efficiency compared to conventional HPLC modes. In this work, Oil in water (o/w) microemulsion has been used for the determination of nifedipine in pharmaceutical preparation. The effect of each parameter on the separation process was examined. The samples were injected into C18, analytical columns maintained at 30°C with a flow rate 1 ml/min. The mobile phase was 87.1% aqueous orthophosphate buffer 15 mM (adjusted to pH 3 with orthophosphoric acid), 0.8% of octane as oil, 4.5 SDS, and 7.6% 1-butanol, all w/w. The nifedipine and internal standard peaks were detected by UV detection at λ max 237 nm The calibration curve was linear (r2=0.9995) over nifedipine concentrations ranging from 1 to 60 μg/ml (n=6). The method has good sensitivity with limit of detection (LOD) of 0.33 μg/ml and limit of quantitation (LOQ) of 1.005 μg/ ml. Also it has an excellent accuracy ranging from 99.11 to 101.64%. The intra-day and inter-day precisions (RSD %) were <0.45% and <0.9%, respectively.

Lower irritation microemulsion-based rotigotine gel: formulation optimization and in vitro and in vivo studies.

BackgroundRotigotine is a potent and selective D1, D2, and D3 dopaminergic receptor agonist. Due to an extensive first-pass effect, it has a very low oral bioavailability (approximately 0.5% in rats).PurposeThe present investigation aimed to develop a microemulsion-based hydrogel for transdermal rotigotine delivery with lower application site reactions.MethodsPseudoternary phase diagrams were constructed to determine the region of oil in water (o/w)-type microemulsion. Central composite design was used to support the pseudoternary phase diagrams and to select homogeneous and stable microemulsions with an optimal amount of rotigotine permeation within 24 hours. In vitro skin permeation experiments were performed, using Franz diffusion cells, to compare rotigotine-loaded microemulsions with rotigotine solutions in oil. The optimized formulation was used to prepare a microemulsion-based hydrogel, which was subjected to bioavailability and skin irritancy studies.ResultsThe selected formulations of rotigotine-loaded microemulsions had enhanced flux and permeation coefficients compared with rotigotine in oil. The optimum microemulsion contained 68% water, 6.8% Labrafil®, 13.44% Cremophor® RH40, 6.72% Labrasol®, and 5.04% Transcutol® HP; the drug-loading rate was 2%. To form a microemulsion gel, 1% Carbomer 1342 was added to the microemulsion. The bioavailability of the rotigotine-loaded microemulsion gel was 105.76%±20.52% with respect to the marketed rotigotine patch (Neupro®). The microemulsion gel irritated the skin less than Neupro.ConclusionA rotigotine microemulsion-based hydrogel was successfully developed, and an optimal formulation for drug delivery was identified. This product could improve patient compliance and have broad marketability.

Micro-Emulsion Phase Behavior of a Cationic Surfactant at Intermediate Interfacial Tension in Sandstone and Carbonate Rocks

Based on the conventional approach, the trapped oil in rock pores can be easily displaced when a Winsor type (III) micro-emulsion is formed in the reservoir during surfactant flooding. On the other hand, the Winsor type (III) involves three phase flow of water, oil, and micro-emulsion that causes considerable oil phase trapping and surfactant retention. This work presents an experimental study on the effect of micro-emulsion phase behavior during surfactant flooding in sandstone and carbonate core samples. In this study, after accomplishing salinity scan of a cationic surfactant (C16–N(CH3)3Br), the effects of Winsor (I), Winsor (III) and Winsor (II) on oil recovery factor, differential pressure drop, relative permeability, and relative permeability ratio were investigated extensively. To carry out a comparative study, homogeneous and similar sandstone and carbonate rocks were selected and the effects of wettability alteration and dynamic surfactant adsorption were studied on them. The results of oil recovery factor in both rock types showed that Winsor (I) and Winsor (III) are preferred compared to Winsor (II) phase behavior. In addition, comparison of normalized relative permeability ratio at high water saturations revealed that Winsor (I) has more appropriate oil and water relative permeability than Winsor (II). The results presented in this paper demonstrate that optimum salinity which results in higher recovery factor and better oil displacement may occur at salinities out of Winsor (III) range. Therefore, the best way to specify optimum salinity is to perform core flood experiments at several salinities, which cover all phase behaviors of Winsor (I), Winsor (III), and Winsor (II).

Alteration of the Structure of Human Stratum Corneum Facilitates Transdermal Delivery

Transdermal transport of pharmacologically active components into the skin depends on the ability of galenic formulations to overcome the stratum corneum (SC) barrier. Microemulsions (ME) are thermodynamically stable liquid systems composed of water, oil and surfactants which may be used for skin permeation and enhance penetration of hydrophobic as well as hydrophilic compounds. We investigated using transmission electron microscopy the effect of ME on human epidermis ex vivo, in order to establish relationship between the type of ME, i.e.: oil-in-water, water-in-oil, gellike, thickened or not with colloidal silica, and the ultrastructural changes in SC barrier resulting from their topical application. ME induced various degrees of dissociation of the SC. The intercellular lipid matrix in the SC became disorganized, which contributed to the separation of corneocytes. This effect was intensified with the increasing oil content in the ME and also when ME were applied under occlusion. The observed morphological changes were in agreement with the increased permeability of ME-treated skin to both lipophilic and hydrophilic compounds reported in the literature. Severe deterioration of the SC barrier induced with the selected ME makes them suitable for selected indications only.

Hydrogen-bonded aggregates in the mixtures of piperidine with water: Thermodynamic, SANS and theoretical studies

Structures resembling semiclathrates probably arise in liquid aqueous solutions of piperidine at the amine mole fraction below 0.03. With the increasing concentration, the structures gradually decay, but the 1:1 complexes of piperidine with water remain linked one to another through the OH⋯O bonds between the hydration water molecules. A periodic order of the bicontinuous microemulsion type occurs in the range of the mole fractions from 0.08 to 0.5. In the piperidine-rich mixtures, the 1:1 complexes are dispersed uniformly in the amine. Relatively low stabilization energy of these complexes probably causes that piperidine is totally miscible with water.

High accuracy NMR chemical shift corrected for bulk magnetization as a tool for structural elucidation of microemulsions. Part 2 – Anionic and nonionic dilutable microemulsions

In our previous report we suggested a new analytical tool, high accuracy NMR chemical shift corrected for bulk magnetization as a supplementary tool to study structural transitions and droplet size and shape of dilutable microemulsions. The aim of this study was to show the generality of this technique and to demonstrate that in almost any type of microemulsion this technique provides additional valuable structural information. The analysis made by the technique adds to the elucidation of some structural aspects that could not be clearly determined by other classical techniques.Therefore, in this part we are extending the study to three additional systems differing in the type of oil phase (toluene and cyclohexane), the nature of the surfactants (anionic and nonionic), and other microemulsion characteristics.We studied sodium dodecyl sulfate (SDS)-based anionic microemulsions with different oils and a nonionic microemulsion based on Tween 20 as the surfactant and toluene as the oil phase. All the microemulsions were fully dilutable with water.We found that the change in the slope of chemical shift against dilution reflects phase transition points of the microemulsion (O/W, bicontinuous, W/O). Chemical shift changes were clearly observed with the transition between spherical and non-spherical (wormlike, etc.) droplet shapes. We compared the interaction of cyclohexane and toluene and used the anisotropic effect of toluene’s ring current to determine its preferred orientation relative to SDS.Chemical shifts of the microemulsion components are therefore a useful addition to the arsenal of techniques for characterizing microemulsions.

Properties of surfactant films in water-in-CO2 microemulsions obtained by small-angle neutron scattering

HypothesisThe formation, stability and structural properties of normal liquid phase microemulsions, stabilized by hydrocarbon surfactants, comprising water and hydrocarbon oils can be interpreted in terms of the film bending rigidity (energy) model. Here, this model is tested for unusual water-in-CO2 (w/c) microemulsions, formed at high pressure with supercritical CO2 (sc-CO2) as a solvent and fluorinated surfactants as stabilizers. Hence, it is possible to explore the generality of this model for other types of microemulsions. ExperimentsHigh Pressure Small-Angle Neutron Scattering (HP-SANS) has been used to study w/c microemulsions, using contrast variation to highlight scattering from the stabilizing fluorinated surfactant films: these data show clear evidence for spherical core–shell structures for the microemulsion droplets. FindingsThe results extend understanding of w/c microemulsions since previous SANS studies are based only on scattering from water core droplets. Here, detailed structural parameters for the surfactant films, such as thickness and film bending energy, have been extracted from the core–shell SANS profiles revealed by controlled contrast variation. Furthermore, at reduced CO2 densities (∼0.7gcm−3), elongated cylindrical droplet structures have been observed, which are uncommon for CO2 microemulsions/emulsions. The implications of the presence of cylindrical micelles and droplets for applications of CO2, and viscosity enhancements are discussed.

Sucrose ester-based biocompatible microemulsions as vehicles for aceclofenac as a model drug: formulation approach using D-optimal mixture design

We assessed the functionality of sucrose esters (sucrose laurate, myristate, palmitate, and stearate), relatively innocuous nonionic surfactants, in formulation of biocompatible microemulsions. The putative influence of surfactant structure on the extension of microemulsion region was explored through the construction of the pseudo-ternary phase diagrams for the isopropyl myristate/sucrose ester-isopropyl alcohol/water system, using the titration method and mixture experimental approach. Minor changes in surfactant tail length strongly affected the microemulsion area boundaries. D-optimal mixture design proved to be highly applicable in detecting the microemulsion regions. Examination of conductivity, rheology, and thermal behavior of the selected sucrose laurate and sucrose myristate-based microemulsions, upon dilution with water, indicated existence of percolation threshold and suggested the phase inversion from water-in-oil to oil-in-water via a bicontinuous structure. Atomic force micrographs confirmed the suggested type of microemulsions and were valuable in further exploring their inner structure. The solubilization capacity of aceclofenac as a model drug has decreased as the water volume fraction in microemulsion increased. High surfactant concentration and the measured solubility of aceclofenac in microemulsion components suggested that the interfacial film may mostly contribute to aceclofenac solubilization.

Structure of Microemulsion Formulated with Monoacylglycerols in the Presence of Polyols and Ethanol

The influence of polyols as cosurfactants (propylene glycol PG; glycerol G) and short chain alcohol as a cosolvent (ethanol EtOH) on the formation and solubilization capacity of the systems: hexadecane/monoacylglycerols (MAG)/polyol/water:EtOH, at 60 °C, was investigated. Electrical conductivity measurement, and the DSC method were applied to determine the structure and type of microemulsions formed. The dimension of the droplets was characterized by DLS. It has been stated that concentration of EtOH has a strong influence on the shape and extend the microemulsion areas and helps to avoid rigid structures such as gels, precipitates, and liquid crystals. It was found that, depending on the concentration of five-component systems, it was possible to obtain fully diluted microemulsions with dispersed particles size distribution ranging from 5 to 30 nm. Studied systems are changing the w/o structure into a bicontinuous system. The results of electrical conductivity showed that the electrical percolation threshold is dependent on the hydration of polar head groups in the whole system and the less rigid interfacial film due to the intercalation of ethanol. In addition, the surfactant/alcohol/polyol can strongly bind water in the inner phase so that it freezes below −10 °C and acts in part as ‘bound’ water. In the systems containing more than 50 mass% of polyols, with respect to the water, the all the water was non-freezable. Propylene glycol and glycerol are cryoprotectants protecting biological systems from massive ice crystallization, since they lower the freezing point of water.

Solution to the absinthe challenge.

In the early 20th century, absinthe was unjustly accused of causing the so-called absinthism syndrome. Nowadays, we know that the thujone content of absinthe was substantially overestimated, because of the crude analytical techniques of that period. Curiously, Dalmatian sage, a flavoring herb commonly found in kitchens, contains more than 50% thujone in its oil [1]. Despite that, no one has yet banned sage from the pantry! Like many other spirits of its kind (for example Greek ouzo, Italian sambuca, or French pastis), absinthe is a herbal distillate containing essential oils [2]. A variety of compounds, for example the monoterpene thujone and the aromatic compound anethol, are dissolved in these oils and contribute to the complex taste of the drink. The compounds dissolved in the essential oils are highly soluble in alcohol but not so in water. Consequently, when cold water is added to the spirit, the alcohol is progressively diluted and the essential oils are eventually forced out of solution. However, for specific proportions of oils, alcohol, and water, we observe the formation of a stable dispersed system, also known as a microemulsion [3]. The metastable region of the system is defined by the area delimited by the binodal and spinodal curves of the phase diagram [4]. This liquid– liquid dispersion contains heterogeneities of size comparable with the wavelength of visible light. These scatter the light in all directions, creating the milky appearance of the liquid [5]. Because these types of microemulsion are metastatic systems, their stability can decrease rapidly with small variations of the physical conditions. Specifically, increasing the temperature leads to growth of the dispersed oil droplets, with consequent deterioration of the emulsion [5]. Therefore, diluting absinthe with cold water will ensure the stability of the microemulsion whereas use of warm water might cause unpleasant phase-separation effects that could make the absinthe drink less enjoyable.

Effect of biopolymer addition on the formulation and properties of an oil-in-water microemulsion

In this study stable microemulsions with very low interfacial tension (IFT) were developed. This type of microemulsion has very low viscosity (very similar to that of water). For application of these systems for solubilization and enhanced oil recovery, we studied the effect on the properties of such microemulsions of adding biopolymer to increase viscosity while maintaining IFT as low as possible. Hydroxyethylcellulose and hydrophobically modified hydroxyethylcellulose were selected; their mode of addition to the formulation is discussed. Microemulsion zones were determined by phase diagram investigation in accordance with Winsor’s classification. In addition to spontaneous formation, transparency, and stability, other properties were measured and others calculated to better define the formulated systems and to confirm the presence of microemulsions. Microemulsion droplet number and size both decrease with increasing salt concentration. Depending on emulsion size, rheological measurements confirm that both polysaccharides have a favourable effect on the viscosity of microemulsion without important modification of IFT.