Microemulsions in separation sciences

Fundamental properties of microemulsions in relation to their utilization in liquid state separation methods of ionic and non-ionic compounds are briefly reviewed. Discussions are focused on some characteristics functions of o/w (L₁) and w/o (L₂) single-phase microemulsions and the two-phase microemulsion systems of Winsor I and Winsor II from the viewpoint of their use as separation media in solvent extraction, liquid chromatography and capillary electrophoresis. Through reviewing, practical advantages of the microemulsion media in the separation of metal ions and biological compounds are assessed.     

Phase behavior of the ternary system H2O-oil-polypropyleneglycol (PPG)

This paper reports on studies of the phase behavior of systems of the type H₂O-oil-amphiphilue-electrolyte with a simple polar polymer as nonionic amphiphile. It turns out that the system behaves similar to systems with monomeric nonionic amphiphiles which is due to the fact that both the binary system H₂O-polar polymer and oil-polar polymer show the same characteristic features as the corresponding systems with monomeric amphiphiles. The results suggest the tailoring of polydetergents by varying both their amphiphilicity and their degree of polymerization in order to obtain highly efficient amphiphiles for the preparation of socalled microemulsions.     

载药微乳液相行为的研究

提出了一种基于相图研究实现纳米药物载体可控制备的方法.采用微乳液控温相图绘制装置绘制了硬脂酸聚烃氧(40)酯(S-40)/聚氧乙烯聚氧丙烯醚嵌段共聚物(F-68)/单硬脂酸甘油酯(GMS)/水体系的拟三元相图,基于电导率测定值确定了微乳液的结构(W/O、双连续相和O/W),该体系同时存在液晶区域.乳化剂S-40/F-68的质量比为7:3.研究了脂溶性药物维甲酸(RA)对微乳液相行为的影响，结果表明RA的加入对微乳液的相行为影响较小.基于相图研究结果制备了维甲酸固体脂质纳米粒(RA-SLN),亚微米粒度分析仪(PCS)测定的平均粒径和透射电镜测试都表明RA-SLN为10 nm左右的球状粒子.     

用于纳米粒子合成的微乳液

微乳液作为纳米反应器的最大优点是可以实现纳米粒子尺寸控制。体系中水的含量、表面活性剂、助表面活性剂等都是控制粒子尺寸的可调因素,研究这些因素对所合成的纳米粒子尺寸以及产量的影响对于实际应用有重要的意义。本文评述了近年来相关的研究进展,对微乳液法在合成纳米粒子中的应用前景作了展望。     

Microemulsions of triglyceride and non-ionic surfactant — effect of temperature and aqueous phase composition

The phase behavior of soybean oil, polyoxyethylene (40) sorbitol hexaoleate and water—ethanol was investigated. Regions of water-in-oil (W/O) microemulsions were determined and were found to be strongly dependent on temperature and water:alcohol ratios. At a water:ethanol ratio of 80/20 (wt.%), an oil:surfactant ratio of 2/3 and a temperature of 25°C, the microemulsion region extended continuously from the oil—surfactant axis to the phase diagram center. However, at the hydrophilic—lipophilic balance (HLB) temperature (20–22°C) and a water:ethanol ratio of 80/20 or 75/25 (wt.%), a single-phase area separated from the original microemulsion region. Conductivity measurements and dynamic light scattering intensifies at 25°C indicated that association structures were formed with increasing aqueous phase concentrations above 15 wt.%. At 20°C, the single-phase scattering intensifies increased sharply with increasing aqueous phase concentrations (38–46 wt.%) and a plateau in the conductivity was detected.

Transmission electron microscopy results supported the finding that more particles are formed with increasing aqueous phase and form connected particles, resulting in constant conductance.     

超临界二氧化碳微乳液中的表面活性剂

介绍了在超临界二氧化碳(SC-CO_2)下形成微乳液的原理和概念,并且按照所应用各种表面活性剂的结构特点对其在SC-CO_2下形成微乳液的能力分别进行比较和归纳,为今后筛选和设计在SC-CO_2下形成微乳液的表面活性剂提供了重要信息。     

Water/i‐Propanol/n‐Butanol Microemulsions

Water and n‐butanol are immiscible. In this paper, i‐propanol was found to be surface active for both water and n‐butanol using surface tension measurement at 25.0±0.1°C, especially the system with i‐propanol in water displays a pronounced decrease in surface tension with a distinct inflexion point indicating aggregation. Investigation on phase behavior of water/i‐propanol/n‐butanol ternary system at 25.0±0.1°C showed i‐propanol could promote remarkably the miscibility of water and n‐butanol. Cyclic voltammetric technique was employed to locate the micro‐regions in single region, indicating the existence of three micro‐regions of water/n‐butanol, n‐butanol/water and bicontinuous region. Thus, a novel water/i‐propanol/n‐butanol microemulsion without general surfactant is expected to form. Dynamic light scattering also demonstrated the size (hydrodynamic diameter) distribution of the microemulsion, verifying further the formation of the microemulsion droplets.     

Phase Behavior of Ternary Systems of the Type H2O?Oil?Nonionic Amphiphile (Microemulsions)

Liquid multicomponent systems of the type H₂O-oil-amphiphile-electrolyte are of growing interest, both in industry and in research. In applications technology, there are two problems to solve: 1. To prepare stable homogeneous solutions of H₂O and nonpolar liquids with as little amphiphile as possible which can be diluted with H₂O in all proportions without phase separation; e.g., concentrated solutions of drugs, herbicides, or insecticides. 2. To prepare stable mixtures of an aqueous, an amphiphile, and an oil phase with as little amphiphile as possible which are employed in tertiary oil recovery and in the pharmaceutical industry. Furthermore, such systems may be used for performing chemical reactions in heterogeneous liquid mixtures with continuously variable properties. In research, such systems are of interest for both experimental and theoretical studies of critical phenomena, especially near so-called tricritical points. Last but not least, their properties may stimulate further research in the field of associated solutions. In this paper we summarize the results of our studies on the phase behavior of ternary systems with nonionic amphiphiles, in particular with respect to the evolution of liquid three-phase bodies. The results suggest that the tricritical points in such systems should be regarded as kinds of pivot points from which the phase behavior evolves. If this were an approach to reality, the phase behavior would be governed in more or less good approximation by universal scaling laws, irrespective of the particular microstructure of the solutions. Finally, we discuss the effect of electrolytes on the phase behavior both in a quaternary phase tetrahedron and a pseudoternary phase prism representation. Although in practice most systems consist of mixtures of oils, amphiphiles, and electrolytes, an understanding of the phase behavior of truly ternary and quaternary systems with chemically well-defined components permits at least qualitative predictions with respect to the phase behavior of the multicomponent mixtures encountered in practice.     

Temperature Effect on the Phase Behavior of the Systems Water/TritonX-100,114,405/n-Butanol/n-Hexane

We have investigated the effect of temperature on the phase behavior and the partition coefficients of nonionic surfactants in water/n-hexane systems. We found that the composition of the conjugate single and two phase solution in the pseudoternary diagram is continuously transformed from one state to other by increasing the temperature. We also demonstrated that the partition coefficient of a nonionic surfactant is a measure of the relative hydrophilic-lipophilic nature of the surfactant, if the measurement is performed at low concentration.     

Microemulsions studies: Correlation between viscosity,electrical conductivity and electrochemical and fluorescent probe measurements

Microemulsion systems involving brine and dodecane, and stabilized by sodium dodecylsulfate and both pentanol and heptanol have been investigated. Results of various experiments including conductivity and viscosity measurements, electrochemical diffusion coefficients and fluorescent probe studies have been gathered and compared in order to gain additional understanding of the microemulsion structure. The diffusion coefficients of hydrophilic hydroquinone and hydrophobic ferrocene obtained from the Levich equation at the rotating disc electrode, vary as the self-diffusion coefficients of water and dodecane, respectively; the results are consistent with those obtained by other workers from tracer or NMR self-diffusion studies. The fluorescence analysis of the polarity sensed by pyrene and the microviscosity felt by dipyrenylpropane suggests that the progressive addition of pentanol and dodecane to SDS micelles leads to solubilizate the probes more in the droplet interior where they experience a more hydrophobic environment. The systematic study of the two microemulsion systems provides insight into the microscopic properties of the oil domains in which the fluorescent probes are assumed to be located. In the system stabilized by n-heptanol as cosurfactant, the microviscosity sensed by P(CH₂)₃P is shown to be much lower than the bulk viscosity of the microemulsion. All the results evidence the well-known structural transitions: water continuous, bicontinuous and oil continuous in the single monophasic area of the brine/ SDS/n-pentanol/dodecane system; premicellar aggregates and water swollen micelles in the W/O area of the brine/SDS/n-heptanol/dodecane system.     

Unimolecular micelles: Synthesis and characterization of amphiphilic polymer systems

Unimolecular micelles were successfully synthesized from mucic acid, fatty acids, and poly(ethylene glycols) to create biocompatible polymers. These polymers consist of a core‐shell structure that resembles conventional micellar structures but with significant thermodynamic stability in aqueous media. The core of the polymers provide a hydrophobic environment for drug encapsulation via hydrophobic interactions, whereas the shell provides excellent water solubility. The polymers were characterized by nuclear magnetic resonance, infrared and mass spectroscopies, as well as gel permeation chromatography, differential scanning calorimetry, and thermogravimetric and elemental analyses. Encapsulation ability was measured using high‐pressure liquid chromatography to monitor lidocaine, a hydrophobic molecule. Encapsulation capabilities increased as lipophilicity of the core increased. To verify that encapsulation was caused by individual unimolecular micelles, surface tension and dynamic light scattering measurements were performed. The results indicated that these unimolecular micelles have great potential as drug carriers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 703–711, 1999     

Criss‐cross amphiphilic polymers and analogous model systems

A new class of amphiphilic polymers carrying two pendant docosyl (C22) chains, located at periodic intervals that are separated by PEG chains of varying lengths, was synthesized via a simple melt‐transesterification polymerization, using dimethyl, 2,5‐didocosyloxyterephthalate as one of the monomers. DSC, variable temperature FT‐IR, and WAXS studies demonstrated that immiscibility between the pendant docosyl units and the backbone PEG segments drives their self‐segregation; this results in the crystallization of the pendant docosyl segments and the generation of a lamellar morphology with the alkyl segments and the PEG chains occupying alternate layers. Based on the study of model criss‐cross amphiphiles that resemble the polymer repeat unit, it is postulated that the chains reconfigure such that both the docosyl chains fold to one side of the terephthalate unit while the PEG segments form a loop on the other side; these chains then organize in a bilayer to form the lamellar structure. The simplicity of the synthesis and the rather unique properties of these polymers suggests that such a design could be translated to develop other interesting functional materials that could exploit the immiscibility‐driven microphase separation for the generation of sub‐10 nm domains; these could have potential applications, such as in membranes, solid polymer electrolyte formulations, and so forth. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1554–1563     

Polymerization of Cationic Surfactant Films in Microemulsions

Properties of microemulsion phases containing mixtures of polymerizable surfactants, single-chain 11-(methacryloyloxy)undecyltrimethylammonium bromide, and double-chain dodecyl-(11-(methacryloyloxy)undecyl)trimethylammonium bromide, and their acrylate analogues have been studied. SANS has shown how film composition, in terms of single-chain surfmer, can be used as a control variable to optimize phase behavior and physicochemical properties of these multi-component systems. A direct comparison between methacrylate and acrylate systems has shown how surfactant molecular structure can influence microemulsion structure; with methacrylates spherical droplets are formed, whereas with the acrylate analogues there is a transition to cylinders. Free-radical polymerization yield partially encapsulated aqueous domains with retention of parent structure.     

Water Solubilization in Mixed Nonionic Surfactants Microemulsions

The systems investigated were water/sucrose laurate/ethoxylated mono-di-glyceride/oleic phase. The oleic phase used first was the pure oils R (+)-limonene, isopropylmyristate, and caprylic-capric triglyceride; these oils were then mixed with ethanol at different mixing ratios (w/w). The total area of the one phase microemulsion region is dependent on the mixing ratios (w/w) of the mixed surfactants and that of the ethanol/oil. The largest microemulsion phase area formed with a surfactants mixing ratio (w/w) equals unity. For the systems where the oleic phase was a mixture of oil and ethanol, the total area of the monophasic microemulsion increases with the increase in the ethanol/oil mixing ratio (w/w). The Gibbs free energy of solubilization was estimated. It increases as the mixing ratio (w/w) of ethoxylated mono-di-glyceride/sucrose laurate increases and with the increase in the ethanol/oil mixing ratio (w/w). The Gibbs free energy of solubilization decreases with the increase in the water content in the water-in-oil microemulsions. The values of the Gibbs free energy of solubilization are higher for oil-in-water microemulsions compared to those of the water-in-oil microemulsions.     

Microemulsions: Effect of alkyl chain length of alcohol and alkane

In microemulsions consisting of four components, i.e. detergent — water — oil — cosurfactant, the free energy of transfer from the continuous oil phase to the interfacial region for the cosurfactant is reported. From the effect of temperature on the free energy, the entropy and the enthalpy values are also reported. The effect of chain length of the alcohol (cosurfactant) is also described. It is further shown, that if the oil phase consists of hexadecane, then the free energy changes as a linear function of the number of carbon atoms in the cosurfactant. On the other hand, if the oil phase is benzene, the cosurfactant chain length has very little effect. These data are analyzed with respect to the microemulsion structure and stability.     

Review article: ion pair potentials for alkali halides and some applications to liquids and defect studies

Abstract

We review the basis on which interionic potentials for alkali halides are obtained. We find that the sizes of the van der Waals terms are known poorly and that the polarizable ion models lack the necessary thermodynamic corrections, however small they may be, to fit low temperature properties of the solid. Although the quantum statistical calculations indicated some damping of van der Waals interactions due to ionic overlap, a systematic study of the basic and modified approaches shows them to be unsatisfactory.     

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 NO_x, soot, and CO₂ were reduced substantially compared to neat diesel, while for the CO the reduction occurs just at low load.      

Synthesis of an amphiphilic polymer having hydrophobic acetal and hydrophilic pyrrolidone moieties and its application to persisting release of aldehyde as a pro‐fragrance

A polymer having acetal moiety in the side chain was synthesized by a reaction of 1,3‐diol structure of poly(vinyl alcohol‐co‐N‐vinylpyrrolidone) and octanal. The hydrophobicity of the resulting acetal moiety and the hydrophilicity of the pyrrolidone moiety allowed the polymer to exhibit amphiphilicity. The polymer released octanal by hydrolysis of the acetal side chains under acidic conditions. The release of octanal was enhanced by the increased hydrophilicity of the polymer because of the presence of pyrrolidone moiety. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3816–3822, 2010