Solubilization, microstructure, and thermodynamics of fully dilutable U-type Brij microemulsion

A U-type microemulsion of Brij 96 has been characterized with respect to the change in cosurfactant, oil chain length on dilution, water solubility, and water solubilization capacity. The phase behavior of the systems has been mapped with different oils. Several techniques, viz., conductivity, optical microscopy, dilution method, absorption, and FT-IR spectroscopy, have been used for microemulsion analysis. The equilibrium within the microemulsion droplets and liquid crystals has been visualized using optical microscopy. The microemulsions have evidenced volume-induced conductance percolation in all the cosurfactants (n₂–n₆ alcohols). The energetics of transfer of alcohol from the bulk oil to the interface has been determined through dilution method. To gain insight into the microenvironment of microemulsion, two optical probes, hydrophilic (Methyl orange) and hydrophobic (Nile red), have been utilized in absorption spectroscopy. Lastly, FT-IR has been explored to observe the state and dissolution behavior of water with increasing weight fraction.     

Formation of Microemulsions in Aqueous NaCl/Sodium (3-Dodecanoyloxy-2-Hydroxy-Propyl) Succinate/Glycerol Mono(2-Ethylhexyl) Ether/Oil Systems

Sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate (SLGMS) forms microemulsions by mixing with cosurfactants such as glycerol mono(2-ethylhexyl) ether (MEH), although the combination with ordinary cosurfactant such as hexanol does not form a microemulsion of large solubilization. The middle-phase microemulsion coexists with excess water and oil (octane) phases at an optimum-mixing fraction of SLGMS and MEH in the presence of salt. The monomeric solubility of MEH in oil is low and MEH is mainly combined with SLGMS at an oil—water interface inside microemulsions. With decreasing salinity, the three-phase body shrinks and eventually disappears. The three-phase body may be terminated at a tricritical point, at which three phases simultaneously coexist. The effect of type of oil on the solubilization capacity of the microemulsions is also discussed.     

Effect of Oil/Water Ratios on the Phase Behavior and the Solubilization Ability of Microemulsion Systems Containing Sodium Dodecyl Sulfate

An α–ε–β fish-like phase diagram of three phase microemulsions was proposed and used to investigate the phase behavior of the microemulsion systems sodium dodecyl sulfate (SDS)/alcohol/oil/water at various oil/water ratios. Related physicochemical properties of the microemulsion systems were calculated. As the oil/water mass ratio increases, the solubility (ε _B) of the alcohol increases, while both the mass fraction of alcohol in the interfacial layer (A ^S) and the solubilization ability (SP ^∗) decrease. The effect of oils on the properties of the microemulsion systems was investigated.     

Effects of Nonpolar Solvents on the Solubilization of Pepsin into Bis(2-Ethylhexyl) Sodium Sulfosuccinate and Cetyltrimethylammonium Bromide Reverse Micelles

Solubilization of pepsin by bis(2-ethylhexyl) sodium sulfosuccinate (AOT) and cetyltrimethylammonium bromide (CTAB) reverse micelles has been studied at 20C. Isooctane, cyclohexane and hexane were used as solvents, and n-butanol, amyl alcohol and hexanol were used as cosurfactants for CTAB. AOT concentrations were varied from 50 to 500 mM and pepsin concentrations were varied from 2 to 10 mg-mL^–1. At 250 mM, AOT can solubilize more than 85% of the Pepsin in each solvent. The effect of aqueous-phase pH on the solubilization of Pepsin has been studied from pH 1 to 8. The maximum solubilization of pepsin was observed below the isoelectric point (pI = 1.5) of the protein at pH 1.0 with 300 mM of AOT. The CTAB solutions were prepared by dissolving CTAB in isooctane with varying concentrations (0–100% v/v) of n-butanol, amyl alcohol or hexanol cosurfactants. It was found that 5% cosurfactant with 100 mM of CTAB was sufficient to solubilize more than 90% of the total pepsin. Pepsin solubilization by AOT reverse micelles increases with increasing polarizability and molar volume of the solvents.     

Formations of polyvinyltoluene microlatexes in quaternary oil in water cetyltrimethylammonium bromide microemulsions

Polymerization of vinyltoluene (VT) in quaternary microemulsions containing cetyltrimethylammonium bromide (CTAB) as the cationic surfactant is studied using laser Raman spectroscopy (LRS) and dilatometry. The influences of water soluble (potassium peroxodisulphate, ammonium peroxodisulphate) and oil soluble (azobisisobutyronitrile, benzoyl peroxide) initiators, monomer, surfactant, cosurfactants (n-alcohol and bifunctional alcohols) and temperature on the rates of polymerization (R _p), energy of activation (Ea), particle diameter (D), number of polymer particles (N _p), molecular weight of polyvinyltoluene (M _v) and number of polymer chains per latex particle (N _pc) are investigated. The dependencies of the kinetic and latex size parameters on the initiators and cosurfactants are discussed in terms of the efficiency of the initiators in initiating the polymerization and on the interfacial partitioning behavior of various cosurfactants. The polymerization mechanism seems to follow Smith Ewart Case II hypothesis with two distinct rate regions. Final polymer microlatexes are found to lie within 10–50 nm as observed by transmission electron microscopy (TEM). Molecular weights are in the range of (1 to 5)×10⁶. Each latex particle contains one to three polymer chains.     

Tuning commercial diesel to microemulsified and blended form: phase behavior and implications

Abstract

Microemulsification and blending of commercial diesel is under constant research for possible fuel application. Microemulsions (ME) were prepared using diesel (D), kerosene (K), diesel and kerosene mixtures at various proportions (D?+?K) (oil phase: O), Triton X-100 surfactant (S), n-butanol, isobutanol (i-butanol), n-pentanol and n-octanol cosurfactants (C), and aqueous phase (W) containing water or brine for the study. Electrical conductance studies and temperature-induced separation of phase have been adopted for recognizing the o/w, w/o and bicontinuous zones. Dye probing has been done to explain the mass transfer among these phases. Percent of solubilization of oil in water has been enumerated in some of the ME. The possible fuel applications of the microemulsions are predicted from their density and flame brightness.     

Synergistic Effect of Mixed Cosurfactants on Transdermal Delivery of Indomethacin from O/W Microemulsion

Since large amounts of oils, surfactants and penetration enhancers used in microemulsion systems might lead to seriously skin irritation, the percutaneous absorption and penetration of indomethacin(IMC, model drug) from O/W microemulsion were enhanced by simply changing the composition of cosurfactants. Pseudo-ternary phase diagrams were constructed with mixed cosurfactants at different ratios. Hairless rat skin was used as a barrier for permeation experiments. Four formulations were prepared with fixed oil, surfactant and different cosurfactant content(4%, 20% and 20%, mass fraction), and formulation F4 with menthol added was evaluated to compare the enhancement effect of it with those of mixed cosurfactants. The O/W microemulsion region was the largest when the mass ratio of ethanol/transcutol was 1:1. However, the region changed slightly for the system with incorporated mixed cosurfactants propylene glycol/transcutol. The flux and skin retention of IMC from O/W microemulsion with mixed cosurfactants were much higher than that with single cosurfactant(P<0.01), while incorporation of menthol would only enhance the drug flux through the skin. To conclude, mixed cosufactants could affect the phase behavior and improve the percutaneous absorption and penetration of IMC. Based on this, it provided a promising solution to enhance drug release from microemulsions without raising potential skin damage.     

Characterization and Antimicrobial Evaluation of Dilution-Stable Microemulsions Against Stenotrophomonas maltrophilia

The purpose of this study is to load glycerol monolaurate (GML) in a microemulsion system for the inactivation of Stenotrophomonas maltophilia. The influence of ethanol, propylene glycol (PG) and sodium benzoate (Na-Bz) on oil solubilization of GML microemulsions is clearly reflected in the phase behavior of these systems. One dilution-stable microemulsion formulation was determined and stable by the examination of the physical stability. Results showed that the microemulsion at 100 ppm, comparable to 3 mg/L ceftazidime, had much higher antimicrobial activities against S. maltophilia, with a major contribution of GML, and Na-Bz enhanced the antimicrobial activities as a hydrotrope.     

POLYMERIZATION IN THE TRANSPARENT WATER-IN-OIL SOLUTIONS (I). METHYL METHACRYLATE AND THE COPOLYMERIZABLE COSURFACTANT

Polymerization of methyl methacrylic acid (MMA) was made in transparent W/O microemulsions and solutions. Acrylic Acid (AA) and pentanol were used as cosurfactants and sodium dodecyl sulfate as surfactant

Acrylic Acid as cosurfactant gave large microemulsion areas with the monomer of methyl methacrylic acid. Polymerization in areas where the microemulsion remained stable gave polymers with high molecular weights 10⁶.     

Characterization of cephalexin loaded nonionic microemulsions

Water/propylene glycol/sucrose laurate/ethoxylated mono-di-glyceride/isopropyl myristate/peppermint oil U-type microemulsions were used to solubilize cephalexin. Microemulsion dilution and interfacial factors contributing to the cephalexin solubilization were evaluated. Cephalexin solubilization capacity increases with the increase in the aqueous phase volume fraction (φ) up to 0.4 then decreases. Electrical conductivity of drug loaded and drug free microemulsions increases with φ. The hydrodynamic radius measured by dynamic light scattering of the oil-in-water loaded microemulsions decreases with temperature. The microemulsions were characterized by the volumetric parameters, density, excess volume, ultrasonic velocity and isentropic compressibility. The microemulsion densities increase with φ up to 0.8 then decrease. The excess volume decreases with φ up to 0.8 then stabilizes. Ultrasonic velocities increase with the increase in φ while isentropic compressibility decreases. Analysis of the volumetric parameters enabled the characterization of structural transition along the microemulsion phase region. The presence of water-in-oil, bicontinuous and oil-in-water microemulsions, at aqueous phase volume fractions below 0.2, between 0.3 and 0.7 and above 0.8, respectively were found. Interfacial properties and dynamic structure of the monolayer for drug loaded and drug free microemulsions, were studied by electron paramagnetic resonance spectroscopy employing the nitroxide spin probe 5-doxylstearic acid. The rigidity of the interface was affected by the water content and also the presence of cephalexin.     

Synthesis of ibuprofen eugenol ester and its microemulsion formulation for parenteral delivery

The purpose of this study was to investigate the possibility of parenteral delivery of poorly water-soluble lipophilic drugs using a phospholipid-based microemulsion system. Ibuprofen eugenol ester (IEE), a highly lipophilic compound, was synthesized from ibuprofen and eugenol, and isolated as an amorphous whitish solid with a melting point at 40.2+/-0.1 degrees C, which structure was confirmed by IR, 1H-NMR and MS spectra. A pharmaceutically acceptable microemulsion system using Miglyol 812, soybean phosphatidylcholine (SbPC) and poly (ethylene glycol) (660)-12-hydroxystearate (Solutol HS-15), and PEG400 and ethanol as oil phase, surfactants and cosurfactants, respectively, was presented and characterized in terms of stability, droplet size distribution (DSD) and their solubilization capacity of IEE. The solubility of IEE in the optimized microemulsion formulation consisting of 6.4% ibuprofen eugenol, 9.6% Miglyol 812, 6% SbPC, 6% HS-15, 8.4% PEG400, 3.6% ethanol and 60% distilled water (w/w) was about 21,000 times higher than that in water. The ibuprofen blood concentration after intravenous administration of microemulsions was determined and compared with that of ibuprofen solution. It was concluded that the presented microemulsion system might be a promising intravenous dosage form of poorly water-soluble lipophilic drugs.     

碳氢表面活性剂在超临界CO2中形成微乳液的研究进展

在超临界CO₂中形成微乳液可以克服CO₂对高分子量和亲水性物质溶解能力差的缺点。碳氢表面活性剂成本低,对环境友好,利用碳氢表面活性剂形成超临界CO₂微乳液有利于工业应用,但绝大部分碳氢表面活性剂不能形成微乳液,所以需要对碳氢表面活性剂进行选择和设计。本文介绍了微乳液的形成、表征和评价,从表面活性剂的亲CO₂性能和界面活性两方面,综述了碳氢表面活性剂的设计思想和进展。另外介绍了助表面活性剂对形成超临界CO₂微乳液的作用,并对常规碳氢表面活性剂在助表面活性剂的作用下形成超临界CO₂微乳液的体系进行了综述。最后,介绍了含碳氢表面活性剂的混合表面活性剂在形成超临界CO₂微乳液方面的研究情况。     

Ionic Equilibria of Chromophoric Reagents in Microemulsions

Protolytic equilibria of twenty chromophoric acid–base indicators from different classes, namely, sulfophthaleins, hydroxyxanthenes, azo compounds, and others, were studied in direct microemulsions of benzene–pentanol-1–surfactant–water at volume fractions of the dispersed phase of up to 13%. Cetylpyridinium chloride, sodium dodecylsulfate, and certain nonionic surfactants were used. Apparent acidity constants (pK _a) of indicators were determined under the conditions of their complete binding by microdroplets (pK _a ^ac). The strong differentiating effect of the dispersed phase of microemulsions of different types on the acid–base properties of indicators was revealed. The effect of the ionic strength of the continuous phase (0.025–1.0) on the values of pK _a ^ac was studied. The partition constants of Bromothymol Blue anions between water and negatively charged microdroplets were estimated. Similarities and differences were revealed in the action of microemulsions and micellar solutions of the corresponding surfactants on the state of the studied chromophoric reagents.     

Properties of microemulsions with sugar surfactants and peppermint oil

In this study, we report on the properties of water + propylene glycol/sugar surfactant/peppermint oil + ethanol. The sugar surfactants were sucrose monolaurate and sucrose dilaurate. The mixing ratios (w/w) of water/propylene glycol and that of ethanol/oil equal 2 and 1, respectively. U-type microemulsions were observed in the sucrose monolaurate while S-type microemulsions were observed in the dilaurate-based systems. Temperature-insensitive microemulsions were formulated using the two surfactants. Water volume fraction percolation thresholds were determined by the study of electrical conductivity and dynamic viscosity. The structural parameters that include the periodicity and the correlation length were estimated using small angle X-ray scattering. The periodicity increases linearly with the increase in the water content whereas the correlation length increases with the increase in the water volume fraction to a certain value then decreases. The diffusion properties investigated by nuclear magnetic resonance confirm a progressive transformation of the microemulsions from water-in-oil to bicontinuous and inversion to oil-in-water upon dilution with water. The hydrodynamic radius of diluted microemulsions measured by dynamic light scattering increases with the increase in temperature. The area per polar head group decreases with the increase in temperature. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

ALTERNATIVE COSURFACTANTS AND COSOLVENTS TO PREPARE MICROEMULSIONS SUITABLE FOR PRACTICAL APPLICATIONS

Some examples of systems including useful ingredients as cosurfactants and cosolventsto furnish suitable microemulsions to be applicated in technological fields such as cosmetics and dermopharmaceuticals, are given For systems with ionic surfactants, the usual cosurfactant (medium chain lenght alcohol) was substituted by more skin compatible ingredients as butyl lactate, or alternatively by oleic acid and a glycol as cosolvent mixed in the aqueous phase of the system. On the other hand, for a system with an alkyl glucoside as nonionic surfactant, temperature - insensitive microemulsions was obtained also with butyl lactate as cosurfactant. Moreover, the influence that the presence of glycols as cosolvents involve on the isotropic liquid regions of such systems has been also evidenced. In conclusion, it is possible to formulate suitable microemulsions to practical applications, overcoming the traditional problems of the most of the conventional microemulsions as are the biological agressivity of the cosurfactant for ionic surfactant systems, and the temperature dependence for nonionic surfactant systems.     

Double-imprinted polymer based on cross-linked poly(vinylimidazole–trimethylolpropane trimethacrylate) in solid phase extraction for determination of lead from wastewater samples by UV–vis spectrophotometry

The monitoring of the heavy metal pollution in wastewater is increasingly becoming a crucial global issue since they tend to accumulate in food chains and can cause many biological abnormalities. In this work, it was developed a novel lead ion-imprinted polymer (IIP) using sodium dodecyl sulphate (SDS) as a second template to be used as adsorbent in solid phase extraction (SPE) for determination of lead from wastewater samples by UV–vis spectrophotometry. The polymer called IIP–SDS was synthesised by a double-imprinting process with lead (template) and SDS (template). IIP–SDS was characterised by infrared spectroscopy Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. IIP–SDS showed good recovery for lead (around 82.0%), while the IIP (only lead as template) was 72.2% and non-IIP was 44.9%. Thus, the double-imprinting process for the preconcentration of Pb²⁺ proved to be a more adequate methodology than IIP with a single template. The optimised parameters of sample preparation were washing solvent (2.0 mL of tetrahydrofuran), type and volume of eluent (5 mL of 1 mol L^?1 hydrochloric acid), sample amount (30 mL of water spiked with 10.0 µg mL^?1), amount of IIP–SDS (400 mg) and sample pH (pH = 4.5). Linearity ranged from 10 to 125 µg L^?1 with r > 0.992. The limit of detection and quantification were 6.3 and 10 µg L^?1, respectively. The precision (relative standard deviation, %) and accuracy (relative error, %) were lower than 15%. Finally, IIP–SDS may be an alternative and effective adsorbent for SPE procedures in monitoring of wastewater samples.     

Studies on the phase behavior and solubilization of the microemulsion formed by surfactant-like ionic liquids with ɛ–β-fish-like phase diagram

The phase behavior and the solubilization of the microemulsion systems surfactant-like ionic liquids 1-hexadecyl-3-methylimidazolium bromide (C₁₆mimBr), 1-tetradecyl-3-methylimidazolium bromide (C₁₄mimBr), or 1-dodecyl-3-methylimidazolium bromide (C₁₂mimBr)/alcohol/alkane/brine have been studied with ɛ–β-fish-like phase diagram method at 40 °C and an oil-to-water mass ratio of 1:1. From the ɛ–β-fish-like phase diagram, the physicochemical parameters, such as the mass fraction of alcohol in the hydrophile–lipophile-balanced interfacial layer (A ^S), and the solubilities of ionic liquid (S ^O) and alcohol (A ^O) in alkane phase, were calculated. The solubilization of the microemulsion system has been discussed based on the ɛ–β-fish-like phase diagram. The smaller the oil molecule, the longer the alcohol chain length, and the larger the NaCl concentration in water, the larger the solubilization of the microemulsion system. In this paper, the solubilization of the microemulsion stabilized by both C₁₂mimBr and sodium dodecyl sulfonate (sodium dodecyl sulfate) was also investigated with the ɛ–β-fish-like phase diagram. The unequimolar composite of anionic and cationic surfactants can avoid the sedimentation aroused by the strong electrostatic attraction, and an obvious synergism effect in solubilization was obtained.     

Solubilization of Styrene and Acrylamide Monomers in Microemulsions

Abstract

Phase diagrams of sodium dodecyl sulfonate (DS)/n‐butanol/styrene/water systems with variable amounts of styrene were constructed at 40°C, and the effects of styrene on microemulsion stability were studied. The solubilization of styrene in these O/W microemulsion systems was investigated by ¹H NMR methods. The results show that the solubilization site shifts from the palisade layer to the inner core of microemulsion droplets when the molar fraction of styrene reaches 0.312. The solubilization of acrylamide in cetyltrimethylmethyl ammonium bromide (CTAB)/n‐butanol/10% n‐octane/water reverse microemulsions (W/O) was studied with a ¹³C NMR method. It was found that the acrylamide was mainly solubilized in the Stern layer of droplets at low acrylamide levels. However, when the mole fraction of acrylamide approaches 0.428, the acrylamide penetrates into the palisade layer and is distributed along the hydrocarbon chain of the surfactant.     

Aqueous solution properties of amphiphilic triblock copolymer poly(p-dioxanone-co-l-lactide)-block-poly(ethylene glycol)

A poly(ethylene glycol) (PEG)-based new amphiphilic block copolymer bearing the poly(p-dioxanone-co-l-lactide) (PPDO/PLLA) hydrophobic moieties was prepared. Depending on the copolymer composition and molecular weights, solubility of the polymeric samples in water was varied. Its diluted aqueous solution properties were studied by viscometry, dye solubilization, ¹H-NMR and dynamic light scattering. 1,6-Diphenyl-1,3,5-hexatriene solubilization and ¹H-NMR spectra carried out in CDCl₃ and D₂O were used to prove the existence of hydrophobic domains as the core of micelle. Average particle size of 60-165 nm with low polydispersity and lower negative zeta (ξ) potential of −3 to −14 mV were observed on the aqueous copolymer dispersion.     

Synthesis of a new ionic imprinted polymer for the extraction of uranium from seawater

The ionic imprinted polymer (IIP) of uranyl ion (UO₂ ²⁺) as the template was synthesized by the formation of binary complexes of UO₂ ²⁺ with 2,4-dioxopentan-3-yl methacrylate as functional monomer followed by thermal copolymerization with ethylene glycol dimethacrylate as cross-linking monomer in the presence of 2,2′-azobisisobutyronitrile as initiator and 1,4-dioxane as porogenic solvent. 50 mmol L^?1 HCl solution was used to leach out UO₂ ²⁺ ions from the IIP. Similarly, the control polymer was prepared under identical experimental conditions without using UO₂ ²⁺ ions. The above synthesized polymers were characterized by infra-red spectroscopy, thermo-gravimetric analysis and Barrett–Emmett–Teller surface area measurement. The maximum adsorption capacities of IIP and CP in (NH₄)₄[UO₂(CO₃)₃] solution were 15.3 and 11.2 mg U g^?1, respectively. The kinetics of adsorption followed a pseudo-second-order rate equation. The prepared IIP was successfully used to extract uranium from real seawater sample.