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Because of the large surface area of colloids interface effects are dominant in contrast to volume effects. The study presents experimental results of the direct transfer of magnetite nanoparticles from an aqueous to a non-miscible organic phase. The starting point is a water-based colloid that is synthesized through a precipitation reaction. The transfer is based on the adsorption of surfactants onto the particle surface at the liquid–liquid interface. While penetrating the liquid–liquid interface, the particles are covered with surfactants and a partial de-agglomeration is initiated. The intention is to produce a stable organic colloid, which has important applications in industry. The optimized process parameters for the successful phase transfer process, the adsorption reactions at the liquid–liquid interface and the stabilization of primary particles in the organic phase are demonstrated.

Magnetic composite particles with a magnetic core consisting of superparamagnetic iron oxide and a cover layer of hydrophobic polyvinylbenzylchloride are described. The magnetite was prepared by precipitation starting with mixed iron II and iron III salts and coating of the solid with oleic acid. The coating is conducted via the liquid–liquid phase transfer. Thereby oleic acid adsorbed on the magnetite surface. In a second step the oleic acid treated magnetite was coated with polyvinylbenzylchloride in a miniemulsion polymerization to get a protective layer. The obtained magnetite core-shell nano-composites with chlorine functionality were characterized by different methods: particle size measurement, acid treatment, iron content, morphology and elemental profiles across the composite particles diameter. The test result reveals the binding of the iron oxide inside the composites which can be also recognize in TEM pictures.

The study presents first experimental results of the transfer of magnetite nanoparticles from an aqueous to a second non-miscible non-aqueous liquid phase. The transfer is based on the adsorption of macromolecular surfactants onto the particle surface at the liquid–liquid interface. For a successful direct phase transfer, it is essential to have cations, like ammonium ions, present in the aqueous phase as well as a threshold concentration of surfactant in the organic liquid phase. While penetrating the liquid–liquid interface, the particles are covered with the surfactant and therefore a partial de-agglomeration is initiated. Based on literature and experimental data a mechanism of surfactant adsorption is proposed. The competing adsorption of the surfactant molecules at the liquid–liquid interface leads to the formation of emulsions and therefore to a hindrance for particles passing the interface. Nevertheless a high efficiency of 100% yield can be reached using optimized process parameters for the phase transfer process.

Durchflussreaktoren werden fur Fallungsreaktionen als Alternative zu den bisher verwendeten Ruhrkesselreaktoren gesehen. Der Einsatz von Ultraschall ermoglicht hier einen definierten, intensiven, lokal begrenzten Energieeintrag in den Verfahrensraum. Diese Reaktoren sind aber bisher wenig untersucht worden und damit am Markt nicht in optimierter Form erhaltlich. Die hergestellten Partikel werden mittels Partikelgrosenanalyse charakterisiert. Der Effekt der Betriebsparameter Ultraschallleistung, Verweilzeit und Hilfswasserstrom auf die Partikelgrose wird herausgearbeitet. Weiterhin werden experimentelle Ergebnisse diskutiert, die sich auf das geometrische Design des Reaktionsraums konzentrieren. Dabei sind die Position des Ultraschallhorns, die Fuhrung der Feed-Strome und die Strategie fur die Bereitstellung des Stabilisierungsmittels von Interesse.

The study presents the transfer of nanoparticles from the aqueous phase to the second nonmiscible nonaqueous liquid phase. The transfer is based on the sedimentation of the dispersed particles through a liquid-liquid interface. First, the colloidal aqueous dispersion is destabilised to flocculate the particles. The agglomeration is reversible and the flocs are large enough to sediment in a centrifugal field. The aqueous dispersion is laminated above the receiving organic liquid phase. When the particles start to penetrate into the liquid-liquid interface, the particle surface is covered with the stabilising surfactant. The sorption of the surfactant onto the surface of the primary particles leads to the disintegration of the flocs. This phase transfer process allows for a very low surfactant concentration within the receiving organic liquid, which is important for further application, that is, synthesis for polymer-nanocomposite materials. Furthermore, the phase transfer of the nanoparticles shows a high efficiency up to 100% yield. The particle size within the organosol corresponds to the primary particle size of the nanoparticles.

The emphasis of the study presented is on a new process of particle extraction to transfer magnetite nanoparticles from an aqueous into an immiscible organic phase directly through the liquid-liquid interface. For the production of high-quality organosols, stabilized colloidal and functionalized particles are required in a liquid organic phase. The mechanism of phase transfer is initiated by adsorption and chemical binding of surfactants (fatty acids) at the particle surface. The resulting physico-chemical dispersion of the hydrophobically modified particles leads to the formation of the stabilized organic colloid, or organosol. The aim here is to demonstrate the entire chain of the transfer process in a continuous miniplant, which comprises particle synthesis, conditioning, and transfer, and which uses a drop column for extraction and as a transfer device. Based on the investigation of the governing principles and the material parameters, the results obtained for the transfer kinetics in the individual contact devices (centrifuge, single-drop column, and drop column for different operations) are used for the dimensioning of the entire process chain.