Abstract:A water-in-oil (w=o) microemulsion was prepared with the zwitterionic surfactant dodecyl betaine (C 12 BE), n-pentanol (C 5 OH), n-heptane (C 7 H 16 ) and water. Effects of polyvinylpyrrolidone (PVP) with different molecular weight on the state of water in w=o microemulsions at a given water=C 12 BE molar ratio were investigated by FT-IR and differential scanning calorimetry (DSC). The experimental results showed that addition of PVP resulted in an increase of the content of the bound water in water pool of a … Show more
“…Moreover, an additional peak around −17 °C can be related to “bound” water nearby the surfactant head groups. Similar results were observed by Xu et al in a poly(vinyl pyrrolidone)-modified microemulsion with a betaine-based surfactant. 5 DSC heating curves of the PDADMAC-modified microemulsions at points P1−P6.…”
This paper is focused on the characterization of polyelectrolyte-modified inverse microemulsions and their use as templates for the synthesis of magnetite nanoparticles. It is shown that the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC) of low molar mass can be incorporated into the individual inverse microemulsion droplets (L2 phase) consisting of heptanol, water, and an amphoteric surfactant with a sulfobetaine head group. Up to a polymer concentration of 20% by weight in the aqueous phase and for different molecular weights of the polymer, an isotropic phase still exists. At a PDADMAC concentration of 10% the area of the isotropic L2 phase is shifted in direction to the water corner. In the percolated area of the L2 phase, i.e., at higher water content, a temperature-dependent change in the conductivity can by observed, and bulk water can be detected by means of differential scanning calorimetry measurements. The unusual temperature-dependent behavior of the polymer-modified system, i.e., the conductivity decrease with increasing temperature, can be explained by temperature-sensitive polyelectrolyte-surfactant interactions, influencing the droplet-droplet interactions. These PDADMAC-modified microemulsions can be successfully used as a template for the formation of ultrafine magnetite particles, in contrast to the nonmodified microemulsion, where the process is misdirected due to the "disturbing" effect of the surfactants. However, in the presence of PDADMAC the surfactant head groups were masked, and therefore magnetite can be synthesized. During the process of magnetite formation the PDADMAC controls the particle growing and stabilizes spherical magnetite particles with a diameter of 17 nm, which can be redispersed without a change in size.
“…Moreover, an additional peak around −17 °C can be related to “bound” water nearby the surfactant head groups. Similar results were observed by Xu et al in a poly(vinyl pyrrolidone)-modified microemulsion with a betaine-based surfactant. 5 DSC heating curves of the PDADMAC-modified microemulsions at points P1−P6.…”
This paper is focused on the characterization of polyelectrolyte-modified inverse microemulsions and their use as templates for the synthesis of magnetite nanoparticles. It is shown that the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC) of low molar mass can be incorporated into the individual inverse microemulsion droplets (L2 phase) consisting of heptanol, water, and an amphoteric surfactant with a sulfobetaine head group. Up to a polymer concentration of 20% by weight in the aqueous phase and for different molecular weights of the polymer, an isotropic phase still exists. At a PDADMAC concentration of 10% the area of the isotropic L2 phase is shifted in direction to the water corner. In the percolated area of the L2 phase, i.e., at higher water content, a temperature-dependent change in the conductivity can by observed, and bulk water can be detected by means of differential scanning calorimetry measurements. The unusual temperature-dependent behavior of the polymer-modified system, i.e., the conductivity decrease with increasing temperature, can be explained by temperature-sensitive polyelectrolyte-surfactant interactions, influencing the droplet-droplet interactions. These PDADMAC-modified microemulsions can be successfully used as a template for the formation of ultrafine magnetite particles, in contrast to the nonmodified microemulsion, where the process is misdirected due to the "disturbing" effect of the surfactants. However, in the presence of PDADMAC the surfactant head groups were masked, and therefore magnetite can be synthesized. During the process of magnetite formation the PDADMAC controls the particle growing and stabilizes spherical magnetite particles with a diameter of 17 nm, which can be redispersed without a change in size.
“…Since reverse micelles are most often regarded as "nano-templates" or "nano-reactors" for the synthesis of nanosized particles, special emphasis in the field of their investigation is, from the point of view of materials synthesis, placed on the attempts to determine their structural parameters, that is primarily micellar sizes and shapes as well as spatial distributions of these parameters. Beside many attempts to model reverse micellar structures, [34][35][36] initiated by the pioneering attempts by Brown and Clarke, 37 within indirect experimental methods that are regularly used in order to determine or evaluate different properties of reverse micelles, are included: light scattering (LS) 38 and small angle neutron scattering (SANS) studies, [39][40][41][42] small angle X-ray scattering (SAXS), 41 quasi-elastic light scattering (QELS), 43 infrared spectroscopy, including FTIR, 44,45 picosecond IR pump-probe spectroscopy 46 and near-IR spectroscopy, 11 dielectric spectroscopy, 47,48 fluorescence light and visible light scattering measurements, 49 X-ray scattering techniques, 50,51 ESR spectroscopy, 52 freeze-fracture etching transmission electron microscopy, 53 NMR, 53,54 measurements of diffusion coefficients, 55 conductometric measurements 29,33,56,57 spectrophotometric measurements, 57,58 shear and extensional viscosity measurements, [59][60][61] photon correlation spectroscopy, 62 fluorescence quenching measurements, 63 dynamic light scattering, 46 Raman spectroscopy, 64 and DSC measurements. 45 In general, spectroscopy has been a p...…”
Section: Basic View Of Reverse Micelles Microemulsions and Their Potmentioning
Reverse micelles as nanosized aqueous droplets existing at certain compositions of water-in-oil microemulsions are widely used today in the synthesis of many types of nanoparticles. However, without a rich conceptual network that would correlate the properties and compositions of reverse micellar microemulsions to the properties of to-be-obtained particles, the design procedures in these cases usually rely on a trial-and-error approach. As like every other science, what is presently known is merely the tip of the iceberg compared to the uninvestigated vastness still lying below. The aim of this article is to present readers with most of the major achievements from the field of materials synthesis within reverse micelles since the first such synthesis was performed in 1982 until today, to possibly open up new perspectives of viewing the typical problems that nowadays dominate the field, and to hopefully initiate the observation and generation of their actual solutions. We intend to show that by refining the oversimplified representations of the roles that reverse micelles play in the processes of nanoparticles synthesis, steps toward a more complex and realistic view of the concerned relationships can be made. The first two sections of the review are of introductory character, presenting the reader with the basic concepts and ideas that serve as the foundations of the field of reverse micellar synthesis of materials. Applications of reverse micelles, other than as media for materials synthesis, as well as their basic structures and origins, together with experimental methods for evaluating their structural and dynamic properties, basic chemicals used for their preparation and simplified explanations of the preparation of materials within, will be reviewed in these two introductory sections. In Secs. 3 and 4, we shall proceed with reviewing the structural and dynamic properties of reverse micelles, respectively, assuming that knowledge of both static and dynamic parameters of microemulsions and changes induced thereof, are a necessary step prior to putting forth any correlations between the parameters that define the properties of microemulsions and the parameters that define the properties of materials synthesized within. Typical pathways of synthesis will be presented in Sec. 5, whereas basic parameters used to describe correlations between the properties of microemulsion reaction media and materials prepared within, including reagent concentrations, ionic strength, temperature, aging time and some of the normally overlooked influences, will be mentioned in Sec. 6. The whole of Sec. 7 is devoted to reviewing water-to-surfactant molar ratio as the most often used parameter in materials design by performing reverse micellar synthesis routes. The mechanisms of particle formation within precipitation synthesis in reverse micelles is discussed in Sec. 8. Synthesis of composites, with special emphasis on silica composites, is described in Sec. 9. All types of materials, classified according to their chemical compositions, that were, to our knowledge, synthesized by using reverse micelles up-to-date, will be briefly mentioned and pointed to the corresponding references in Sec. 10. In Sec. 11, some of the possible future directions for the synthesis of nanostructured materials within reverse micelles, found in combining reverse micellar syntheses and various other synthesis procedures with the aim of reaching self-organizing nanoparticle systems, will be outlined.
“…9b we can see that there are no obvious changes in the sub-peak positions after adding PVP-K30 to the reversed micelle at x 0 =15. The contents of different water states are obtained according to reference [39] and listed in Fig. 10.…”
Section: Viscosities Of the Aot Reversed Micelles In The Presence Of mentioning
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