Microemulsions: Options To Expand the Synthesis of Inorganic Nanoparticles

Microemulsions (MEs) are ideal for obtaining high‐quality inorganic nanoparticles. As thermodynamically stable systems with a nanometer‐sized droplet phase that serves as a nanoreactor, MEs have obvious advantages for the synthesis of nanoparticles. MEs also have disadvantages, such as their complexity as multicomponent systems, the low amount of obtainable nanoparticles, their limited thermal stability, the fact that hydrolyzable or oxidizable compounds are often excluded from synthesis, the partly elaborate separation of nanoparticles, as well as the removal of surface‐adhered surfactants subsequent to synthesis. This Review presents some strategies to further expand the options of ME‐based synthesis of inorganic nanoparticles. This comprises the crystallization of nanoparticles in “high‐temperature MEs”, the synthesis of hollow nanospheres, the use of hydrogen peroxide or liquid ammonia as the polar droplet phase, and the synthesis of base metals and nitrides in MEs.     

CTAB反相微乳液体系稳定性的影响因素

研究温度、pH值和盐浓度对CTAB(十六烷基三甲基溴化铵)/正丁醇/正辛烷/水(或钨酸钠溶液)反相微乳液体系稳定性的影响,并绘制了该反相微乳体系的拟三元相图.实验结果表明:表面活性剂与助表面活性剂的配比对该微乳液的稳定性有显著影响,当CTAB与正丁醇质量比为2: 3时,体系有较大的反相微乳液稳定区;该微乳液体系对温度变化不敏感;pH值为1～7范围内时,该体系具有较好的pH值稳定性;钨酸钠溶液浓度在0.05～0.08 g/mL时,盐浓度对整个微乳区影响不大.结果表明:该反相微乳液体系可作为微型反应器用于纳米粒子的制备.     

Water‐in‐Oil Micro‐Emulsion Enhances the Secondary Structure of a Protein by Confinement

A scheme is presented in which an organic solvent environment in combination with surfactants is used to confine a natively unfolded protein inside an inverse microemulsion droplet. This type of confinement allows a study that provides unique insight into the dynamic structure of an unfolded, flexible protein which is still solvated and thus under near‐physiological conditions. In a model system, the protein osteopontin (OPN) is used. It is a highly phosphorylated glycoprotein that is expressed in a wide range of cells and tissues for which limited structural analysis exists due to the high degree of flexibility and large number of post‐translational modifications. OPN is implicated in tissue functions, such as inflammation and mineralisation. It also has a key function in tumour metastasis and progression. Circular dichroism measurements show that confinement enhances the secondary structural features of the protein. Small‐angle X‐ray scattering and dynamic light scattering show that OPN changes from being a flexible protein in aqueous solution to adopting a less flexible and more compact structure inside the microemulsion droplets. This novel approach for confining proteins while they are still hydrated may aid in studying the structure of a wide range of natively unfolded proteins.     

Synthesis of polydimethylsiloxane microemulsions by self-catalyzed hydrolysis/condensation of dichlorodimethylsilane

The preparation of PDMS microemulsions was carried out by adding at controlled rate dichlorodimethylsilane (DCMS) in a solution of sodium dodecylpolyoxyethylene(8) sulphate. The instantaneous hydrolysis of DCMS and subsequent condensation of the corresponding dihydroxysilane generate dispersions of cyclosiloxanes of small lengths (4 to 6 D units). The high load of chloride ions released during the hydrolysis step requires the presence of the above-mentioned electrosteric surfactant to avoid rapid coagulation of the dispersion. In addition, its sulphate end-group captures a proton that catalyses the ring-opening polymerization of cyclosiloxane as well as the polycondensation of disilanol PDMS chains. Final particles exhibit a diameter of about 50 nm for a polydispersity index of less than 1.1. They are constituted of PDMS chains exclusively linear ( ; ) and of small cycles in low contents (less than 5 wt% in the best conditions). To cite this article: G. Palaprat, F. Ganachaud, C. R. Chimie 6 (2003).     

Hydrodynamic effects in bicontinuous microemulsions measured by inelastic neutron scattering

The dynamical properties of bicontinuous microemulsions have been studied with neutron spin echo spectroscopy around length scales corresponding to the correlation peak q₀. Comparison of samples with different contrasts for neutrons shed light on the two modes dominated either by variation of the oil/water difference or surfactant concentration in the hydrodynamic regime. The results have been compared to theoretical predictions of the relaxation rates of bicontinuous microemulsions by Nonomura and Ohta [M. Nonomura, T. Ohta, J. Chem. Phys. 110, 7516 (1999)]. The influence of modification of the surfactant layer bending constants in the microemulsion by addition of homopolymers (polyethylenepropylene: PEP_X and polyethyleneoxide: PEO_X, X=5 kg/mol), dissolved in the oil phase and water, has been investigated.     

Applications of emulsified systems in elemental analysis by spectroanalytical techniques

Emulsified systems are characterized by an immiscible liquid dispersed in another liquid in the form of droplets. These systems can be classified according to the size of the dispersed droplets obtained in coarse emulsions (0.5–50 µm) or microemulsions (0.01–0.10 µm). These systems have several properties that make them interesting in several fields of technology, and the emulsion formed by oil droplets dispersed in an aqueous phase (O/A) is the most used in analytical determinations due to its low viscosity and organic load. This paper discusses the characteristics of emulsified systems, their obtention, stabilization, properties and use in the development of analytical methods for elemental analysis in matrices with high organic content such as oils, fatty foods and fuel matrices.     

Solution of telechelic ionomers in water/AOT/oil (w/o) microemulsions: a static and dynamic light scattering study

Static and quasielastic light-scattering measurements of endsulfonated polyisoprene in a water in oil (w/o) microemulsions were used to characterize the structure and diffusion properties of this complex system. The hydrophilic end groups of the polymer stick to the surfactant covered oil/water interface, thus bridging the water droplets. This structure formation decreases the mobility of the aqueous nanodroplets and polymer molecules. At interdroplet distances larger than the end-to-end distance of the ionomer chain a decrease of the osmotic modulus is observed. It can be explained by a depletion force of free ionomer chains acting on the nanodroplets. With increasing polymer concentration structure formation of the microemulsion is observed at nanodroplet concentrations where the ionomer chains just fit the average separation of two nanodroplets.