Determination of water states and the structural parameters of W/O microemulsions

The states of water in sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/isooctane/water reverse(W/O) microemulsions system have been investigated by using Fourier transform infrared spectroscopy(FT-IR) technique. The broad peak obtained for hydroxy(O-H) of water has been resolved by least square curve-fitting. It has been observed that the water solubilized in microemul-sion droplets has four states, i.e. bound water with sulfo-group, free water, bound water with sodium counterion in the water pool of microemulsion droplets and a small amount of trapped water in the palisade layer of microemulsion droplets. The following have also been determined: the aggregation number (n), the radius of the water pool in the microemulsions(rw), the thickness of the bound water with sulfo-group(d1), the thickness of the bound water with sodium counterion(d2), the total thickness of the bound water (d) and the effective area of head groups of AOT(AAOT).     

Diffusion behavior of pharmaceutical O/W microemulsions studied by dynamic light scattering

Dynamic light scattering experiments have been performed at various concentrations, of pharmaceutical oil-in-water microemulsions consisting of Eutanol G as oil, a blend of a high (Tagat O2) and a low (Poloxamer 331) hydrophilic–lipophilic balance surfactant, and a hydrophilic phase (propylene glycol/water). We probe the dynamics of these microemulsions by dynamic light scattering. In the measured concentration range, two modes of relaxation were observed. The faster decaying mode is ascribed classically to the collective diffusion D _c (total droplet number density fluctuation). We show that the slow mode is also diffusive and suggest that its possible origin is the relaxation of polydispersity fluctuations. The diffusion coefficient associated with this mode is then the self-diffusion D _s of the droplets. It was found that D _c and D _s had opposite volume fractions of oil plus surfactants (ϕ) dependence and a common limiting value D ₀ for ϕ=0. Average hydrodynamic radius (R _h=10.5 nm) of droplets was calculated from D ₀. R _h is supposed to compose the inner core, a surfactant film including possible solvent molecules, which migrate with the droplet. The concentration dependence of diffusion coefficients reflects the effect of hard sphere and the supplementary repulsive interactions which arises due to loss of entropy, when absorbed chains of surfactant intermingle on the close approach of the two droplets. This mechanism could also explain the observed stability of our systems. The estimated extent of polydispersity is 0.22 from the amplitude of slower decaying mode. The polydispersity in microemulsion systems is dynamic in origin. Results indicate that the time scale for local polydispersity fluctuations is at least three orders of magnitude longer than the estimated time between droplet collisions.     

Nanoscopic microheterogeneities or pseudo-phase separations in non-conventional liquids

This article discusses new concepts in macroscopically monophasic colloidal systems, where entropy is a major driving force for very subtle interactions and structuring. First, we show how microemulsion-similar structures can be achieved with hydrotropes. These aggregates are less defined in structure and of shorter lifetime than classical micelles but still potentially useful microheterogeneities with internal interfaces. The other extreme case of strong interactions is given when cationic and anionic surfactants are mixed in equimolar ratios. It is well known that surfactants can be made more soluble when ethylene oxide groups are incorporated. This strategy is applied for such ‘catanionics’ to avoid surfactant precipitation. Finally, we consider the fact that ethylene oxide groups increase the size of the hydrophilic headgroups of carboxylates so that the geometrical constraints compel a direct spherical shape even in the absence of water. As a result, ‘water-free direct microemulsions’ with only charged surfactants and oil are conceivable.     

Phase transition induced bywater dilution in phospholipid U-type food-grade microemulsions studied by DSC

In this study we used differential scanning calorimetry to clarify the role of water activity within the nano-droplets, and to explore phase transitions in novel phospholipids based fully dilutable food-grade microemulsions. The microstructure transitions were investigated along two water dilution lines (50:50 and 80:20 mass% surfactant mixture/oil phase). From the water thermal behavior we learned that three structural regions can be identified along the water dilution lines. The thermal transition points coincide with the structural phase transition of the microemulsions as measured by other methods (electrical conductivity and SD-NMR measurements). The structural transitions were detected at 20 and 45 mass% of water along dilution line 55, where along dilution line 82 it occurs at 40 and 50 mass% of water. The microemulsions along dilution line 82 seem to have more compact surfactant packing film, thus the film has stronger resistance to transformation upon dilution, resulting in a smaller bicontinuous region than the one formed at dilution line 55. The difference in phase transition point can be used for triggering the release of future solubilizate.     

Structural studies of 1-butyl-3-methylimidazolium tetrafluoroborate/TX-100/ p-xylene ionic liquid microemulsions.

The ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) forms nonaqueous microemulsions with p-xylene, with the aid of the nonionic surfactant TX-100. The phase behavior of the ternary system is investigated, and three microregions of the microemulsions-ionic liquid-in-oil (IL/O), bicontinuous, and oil-in-ionic liquid (O/IL)-are identified by conductivity measurements, according to percolation theory. On the basis of a phase diagram, a series of IL/O microemulsions are chosen and characterized by dynamic light scattering (DLS). The size of aggregates increases on increasing the amount of added polar component (bmimBF(4)), which is a similar phenomenon to that observed for typical water-in-oil (W/O) microemulsions, suggesting the formation of IL/O microemulsions. The microstructural characteristics of the microemulsions are investigated by FTIR and 1H NMR spectroscopy. The results indicate that the interaction between the electronegative oxygen atoms of the oxyethylene (OE) units in TX-100 and the electropositive imidazolium ring may be the driving force for the solubilization of bmimBF4 into the core of the TX-100 aggregates. In addition, the micropolarity of the microemulsions is investigated by using methyl orange (MO) as a UV/Vis spectroscopic probe. A relatively constant polarity of the microemulsion droplets is obtained in the IL microemulsion. Finally, a plausible structure for the IL/O microemulsion is presented.     

Aqueous and nonaqueous microemulsions with high molecular weight alkanes

This study extends the existing phenomenological thermodynamic model of aqueous microemulsions to nonaqueous microemulsions and examines the phase patterns when the melting temperature of the alkane oil is in the range of other liquid-liquid transition temperatures. The liquid paraffins studied are the alkane oils of greater than 17 carbons and are solid at room temperature. Water, water and ethylene glycol (41 by wt.), propylene glycol and water (41 by wt.), and propylene glycol are the four non-oleic components examined. Homogeneous polyoxyethylene nonionic surfactants and the commercial surfactants of the Brij series, Neodol series, and the LP series were used. Small-angle x-ray scattering gives evidence for the presence of microstructures in these solutions and, thus these systems are true microemulsions at temperatures above the melting point of the alkane. Systematic paths to move from aqueous to nonaqueous microemulsions are outlined. These results are utilized in optimizing the performance requirements of an inkjet printing application.     

A review of methods for synthesis of nanostructured metals with emphasis on iron compounds

Synthesis of metal nanoparticles with specific properties is a newly established research area attracting a great deal of attention. Several methods have been put forward for synthesis of these materials, namely chemical vapor condensation, arc discharge, hydrogen plasma—metal reaction, and laser pyrolysis in the vapor phase, microemulsion, hydrothermal, sol-gel, sonochemical, and microbial processes taking place in the liquid phase, and ball milling carried out in the solid phase. The properties of metal nanoparticles depend largely on their synthesis procedures. In this paper the fundamentals, advantages, and disadvantages of each synthesis method are discussed.     

反相微乳液法制备核壳型磁性SiO2微球及其表征

目的 以FeCl3和FeCl2为水相,以甲苯为油相,以正硅酸乙酯为硅源制备核壳结构的SiO2磁性微球.方法 采用反相微乳液法一步法制备出磁性微球,并利用透射电镜、场发射扫描电镜、X射线衍射仪、能谱仪和振动样品磁强计分别对微球的形貌、粒度分布、物相组成、化学成分和磁性能进行表征.结果 采用反向微乳液法制备的SiO2磁性微球显示出良好的核壳结构,粒径分布在100～200nm之间,主要物相是无定形的SiO2和立方尖晶石型的Fe3O4,并保持了Fe3O4磁性粒子的超顺磁性.结论 采用该方法制备的核壳型磁性SiO2微球性质稳定,是一种优异的生物磁性材料.     

阳离子表面活性剂中相微乳的形成和特性

自1943年SdriAn。等人山发现微乳液体系并予以命名以来，对微乳液研究不断深入·微乳液是由油、水、表面活性剂和助表面活性剂组成的各向同性、透明的、热力学稳定的分散体系，微乳液可分为单相微乳液和多相微乳液问．中相微乳液是多相微乳液中，与过剩盐水相和过剩油相达到三相平衡的Winsor皿型微乳液，它在三次采油、日用化工、微环境、酶催化等方面具有特殊重要的应用I‘，‘］．近年来对阴离子表面活性剂中相微乳液的形成和特性进行了较多研究［5。8］．但对阳离子表面活性剂中相微乳液的研究，目前尚未见报导，本文以澳代十四烷基毗…