Search results for "Microemulsion"
showing 10 items of 99 documents
Microwave radiation effect on the synthesis of cadmium sulphide nanoparticles in water in oil microemulsion: a preliminary study at different frequen…
2004
AbstractCadmium sulphide nanoparticles have been synthesised in water/sodium bis (2-ethylhexyl) sulfosuccinate (AOT)/n- heptane microemulsions kept at 30 °C by microwave irradiation coupled with water-cooling and in conventional thermostatic conditions at the same temperature. The study has been performed exposing the reaction media to microwave radiation at five different frequencies (2.45, 2.85, 8, 12 and 18 GHz). For each frequency, a suitable microwave exposure set-up has been assembled. During the growth process, the dimensions of the nanoparticles have been characterised by means of UV-Vis spectroscopy. At the end of the growth process, the surface morphology of the nanoparticles has …
Configurational entropy of microemulsions : The fundamental length scale
1993
Phenomenological models have been quite successful in characterizing both the various complex phases and the corresponding phase diagrams of microemulsions. In some approaches, e.g., the random mixing model (RMM), the lattice parameter is of the order of the dimension of an oil or water domain and has been used as a length scale for computing a configurational entropy, the so‐called entropy of mixing, of the microemulsion. In the central and material section of this paper (Sec. III), we show that the fundamental length scale for the calculation of the entropy of mixing is of the order of the cube root of the volume per molecule—orders of magnitude smaller than the dimension of such a domain…
Oscillations in the dynamics of temperature-driven phase separation
1997
We examine the dynamics of the phase separation of a single phase of water-in-oil microemulsion droplets towards a phase of smaller droplets coexisting with a water-rich phase. Oscillations are observed in the turbidity of the mixture and in the specific heat, when this transition is induced by a continuous temperature increase. The oscillations indicate an unusual type of dynamics which involves an energy barrier only to be overcome by a large number of droplets collectively. It is due to the spontaneous curvature of the water-oil-interface, and conservation of volumes.
Composite nanoparticles based on hyaluronic acid chemically cross-linked with alpha,beta-polyaspartylhydrazide.
2007
In this paper, new composite nanoparticles based on hyaluronic acid (HA) chemically cross-linked with alpha,beta polyaspartylhydrazide (PAHy) were prepared by the use of a reversed-phase microemulsion technique. HA-PAHy nanoparticles were characterized by FT-IR spectroscopy, confirming the occurrence of the chemical cross-linking, dimensional analysis, and transmission electron micrography, showing a sub-micrometer size and spherical shape. Zeta potential measurements demonstrated the presence of HA on the nanoparticle surface. A remarkable affinity of the obtained nanoparticles toward aqueous media that simulate some biological fluids was found. Stability studies showed the absence of chem…
A Study of the Separation of 1-Dodecene and 1-Tetradecene Hydroformylation Products in Aqueous Medium
2009
Abstract Experimental results of the solubilization of olefins in hydroformylation model systems, comprising 1-dodecene and 1-tridecanal or 1-tetradecene and 1-pentadecanal, water, butanol, sodium dodecylsulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), and/or tri(m-sulfofenyl)phosphine trisodium salt (TPPTS-Na) are presented. The selected systems were used for the hydroformylation of 1-dodecene and 1-tetradecene whereby high yields of aldehydes were obtained. After the reaction, the mixture spontaneously separated into an organic phase with the reaction products and an aqueous phase comprising the catalyst and excess phosphine ligand.
Tuning size and thermal hysteresis in bistable spin crossover nanoparticles.
2010
Nanoparticles of iron(II) triazole salts have been prepared from water-organic microemulsions. The mean size of the nanoparticles can be tuned down to 6 nm in diameter, with a narrow size distribution. A sharp spin transition from the low spin (LS) to the high spin (HS) state is observed above room temperature, with a 30-40-K-wide thermal hysteresis. The same preparation can yield second generation nanoparticles containing molecular alloys by mixing triazole with triazole derivatives, or from metallic mixtures of iron(II) and zinc(II). In these nanoparticles of 10-15 nm, the spin transition "moves" towards lower temperatures, reaching a 316 K limit for the cooling down transition and mainta…
Thermodynamic and kinetic properties of water–oil–surfactant mixtures
1998
Abstract We present experimental data on thermodynamic and kinetic properties of the emulsification failure of a droplet-phase microemulsion, and model them by a bending free energy. In contrast to most other models used to describe water–oil–surfactant mixtures no entropic contributions are included in the present description. Still, there is quantitative agreement between theory and measurements, even though there are no free parameters in our model – only experimentally accessible material constants appear.
On multi-scale percolation behaviour of the effective conductivity for the lattice model with interacting particles
2015
Recently, the effective medium approach using 2x2 basic cluster of model lattice sites to predict the conductivity of interacting droplets has been presented by Hattori et al. To make a step aside from pure applications, we have studied earlier a multi-scale percolation, employing any kxk basic cluster for non-interacting particles. Here, with interactions included, we examine in what way they alter the percolation threshold for any cluster case. We found that at a fixed length scale k the interaction reduces the range of shifts of the percolation threshold. To determine the critical concentrations, the simplified model is used. It diminishes the number of local conductivities into two main…
Dynamics of Pattern Formation in Biomimetic Systems
2008
This paper is an attempt to conceptualize pattern formation in self-organizing systems and, in particular, to understand how structures, oscillations or waves arise in a steady and homogenous environment, a phenomenon called symmetry breaking. The route followed to develop these ideas was to couple chemical oscillations produced by Belousov-Zhabotinsky reaction with confined reaction environments, the latter being an essential requirement for any process of Life. Special focus was placed on systems showing organic or lipidic compartments, which represent more reliable biomimetic matrices.
Rate Effects of AOT-Stabilized Microemulsions on Reactions of Ligand Substitution in Cationic Palladium(II) Complexes
1998
Rate data for the substitution reactions of the coordinated ligand X (=2,2‘-bipyridine or 4,4‘-dimethyl-2,2‘-bipyridine) of the palladium(II) complex [Pd(en)X]2+, where en = ethylenediamine, by en or N,N-dimethylethylenediamine in heptane−AOT−water microemulsions have been obtained at 25.0 °C as a function of the AOT concentration at the constant R (=[H2O]/[AOT]) values of 3, 8, and 20 or 30. The overall second-order rate constants are higher in microemulsions than in bulk water and decrease significantly as both the AOT concentration (at constant R) and the molar ratio R (at a given [AOT]) increase. The quantitative analysis of the kinetic data, made by applying the pseudophase model, lead…