Concentrated magnetic fluids on water and short chain length organic carriers (original) (raw)
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Journal of colloid and interface …, 1991
A comparison of the ability of C6-Cj8 carboxylic acids to stabilize aqueous magnetite fluids is made. Micelle formation prevented complete dispersion of magnetite by stearic and myristic acids, but was overcome by introducing the acid in several portions. Improvements in fluid preparation are reported, achieved by perchloric acid treatment of surfactant-stabilized magnetite produced in basic solution, followed by redispersion of the particles in dilute base. The quantity of surfactant in the primary layer has been determined for C~0-Cl8 acids, and the particle surface area occupied per molecule of surfactant found to range between ca. 21 and 38 ~2. For decanoic and myristic acids the groups pack efficiently and form a "condensed" film over the surface of the particles. Ammonium and monomethylammonium salts of the same acids were used in attempts to form the secondary layers. Ammonium salts produced dispersion in all cases except Sarkosyl-"O," whereas MeNH~ salts of oleic and myristic acids were successful. Quantitative data on the relative amounts of surfactant in each layer are presented and discussed.
Journal of Magnetism and Magnetic Materials, 2002
The preparation procedure for very concentrated magnetic fluids on various polar liquids, especially on C 3-C 10 (propanol, y, decanol) alcohol carriers is presented. Double layer sterical stabilization mechanism ensured the high colloidal stability of samples, up to the limiting value of the hydrodynamic volume fraction (B0.65), corresponding to saturation magnetization values of about 70 kA/m. The low-field part of the reduced magnetization curve of the most polar high concentration propanol sample is compared to those corresponding to low and medium concentration waterbased samples.
Sterically stabilized water based magnetic fluids: Synthesis, structure and properties
Journal of Magnetism and Magnetic Materials, 2007
Magnetic fluids (MFs), prepared by chemical co-precipitation followed by double layer steric and electrostatic (combined) stabilization of magnetite nanoparticles dispersed in water, are presented. Several combinations of surfactants with different chain lengths (lauric acid (LA), myristic acid (MA), oleic acid (OA) and dodecyl-benzene-sulphonic acid (DBS)) were used, such as LA+LA, MA+MA, LA+DBS, MA+DBS, OA+DBS, OA+OA and DBS+DBS. Static light scattering, transmission electron microscopy, small angle neutron scattering, magnetic and magneto-rheological measurements revealed that MFs with MA+MA or LA+LA biocompatible double layer covered magnetite nanoparticles are the most stable colloidal systems among the investigated samples, and thus suitable for biomedical applications. r
Nanomaterials
The present work reports the synthesis of a stable aqueous magnetic fluid (AMF) by dispersing double-surfactant-coated Fe3O4 magnetic nanoparticles (MNPs) in water using a facile ambient scalable wet chemical route. MNPs do not disperse well in water, resulting in low stability. This was improved by dispersing double-surfactant (oleic acid and sodium oleate)-coated MNPs in water, where cross-linking between the surfactants improves the stability of the AMFs. The stability was probed by rheological measurements and all the AMF samples showed a good long-term stability and stability against a gradient magnetic field. Further, the microwave spin resonance behavior of AMFs was studied in detail by corroborating the experimental results obtained from the ferromagnetic resonance (FMR) technique to theoretical predictions by appropriate fittings. A broad spectrum was perceived for AMFs which indicates strong ferromagnetic characteristics. The resonance field shifted to higher magnetic fiel...
Structural Aspects of Stabilization of Magnetic Fluids by Mono-Carboxylic Acids
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The structure of magnetic fluids (magnetite in decahydronaphtalene) stabilized with saturated mono-carboxylic acids of different chain lengths (lauric, myristic, palmitic and stearic acids) is studied by means of magnetization analysis and small-angle neutron scattering. It is shown that magnetite nanoparticles are dispersed in the carrier approximately with the same size distribution whose mean value and width are significantly less as compared to the classical stabilization with non-saturated oleic acid. The found thickness of the surfactant shell around magnetite is analyzed with respect to stabilizing properties of mono-carboxylic acids.
Rheological properties of water-based magnetic fluid and its emulsion
Journal of Magnetism and Magnetic Materials, 2005
Field-induced rheological properties were studied for pure magnetic fluids (MFs) and 5% MF-cetyltrimethylammonium bromide (CTABr) emulsion for varying CTABr concentration (0-0.1 M) at different temperatures. The zero-field rheological study for 5% MF-CTABr emulsion shows maximum viscosity for 0.01 M CTABr concentrations. In-field viscosity results for 0.01 M CTABr-MF emulsion shows nearly 10 times more change in viscosity than the pure fluid, indicating the interaction between micelles and magnetic particles. r
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Soft Matter, 2012
Emulsions are mixtures of two or more immiscible fluids, stabilised by interfacial adsorption of surfactants or particles. As such emulsions are essential components in multifarious processes and products, such as foods, pharmaceutical and agrochemical formulations, paints, inks, lubricants, oils and oil recovery. Stability and structure of responsive colloids and emulsions can be controlled by changes in composition, pH, as well as by external stimuli temperature, pressure and light. This is the first report of easy to formulate magnetically responsive emulsions stabilized by a new class of magnetic surfactant stabilizers.
International Journal of Thermophysics, 2012
The effect of the molecular weight of poly(ethylene glycol) (PEG) on the physical properties of water-based magnetic fluids with sodium oleate and PEG stabilization was investigated. The structure as well as magnetic, rheological, and thermal properties of the obtained samples were studied using transmission electron microscopy (TEM), photon cross correlation spectroscopy (PCCS), superconducting quantum interference device (SQUID), and differential scanning calorimetry (DSC) methods. The molecular weight of PEG had a strong effect on the rheological properties while the effect was rather insignificant on the particle size distribution and the self-heating of the studied magnetic fluids. The heating ability of the PEG-stabilized magnetic fluids was determined by calorimetric measurements of the specific absorption rate (SAR). The thickness of the PEG layer was calculated from the experimental data of the temperature rise rates as a function of the magnetic field strength using the Rosensweig theory.
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