Encapsulation of magnetic particles

Zhang QY, Xie G, Zhang HP, et al. (2(X)7) Encapsulation of magnetic particles via miniemulsion polymerization of styrene. II. Effect of some parameters on the polymerization of styrene. J Appl Polym Sci 105 3525-3530... 

The effect of the amount of surfactant SDS, hydrophobe hexadecane, iron oxide magnetic particles, MAA and non-ionic cellulose ether, hydroxyethylcellulose, on the magnetic latex morphology, surface quality and size distribution was studied by Forcada et al. for the encapsulation of magnetic particles by miniemulsion polymerization of St. Optimal conditions were 2-3% of SDS, 9-12% of hexadecane, 10% of iron oxide and 2% of HEC, relative to the total amount of St and iron oxide [177]. 

Encapsulation of magnetic particles into polymeric nanofibers. Reprinted with permission from reference 88. Copyright 2006 Elsevier. 

Emulsion polymerization techniques have also been used for the direct encapsulation of magnetic particles [113,114]. A double layer of surfactant was generally used (sodium oleate combined with sodium dodecyl benzene sulfonate). The method yielded up to 20 wt% of encapsulated magnetite into polystyrene polydis-perse latex particles. Sometimes, the formation of large amounts of coagulum could not be avoided [113a]. 

Cationic PNIPAM-covered magnetic particles Hetero coagulation of iron oxide nanoparticles onto cationic particles. Encapsulation of preformed particles by polymerization of NIPAM, BAM and AEMH 300-1000 nm Superparamag-netic, bioreactive particles. Temperature, salinity and pH sensitive [10,18,19]... 

The novel properties of magnetic nanoparticles are in focus of many fundamental research and practical applications [1,2], It is difficult to prevent metallic magnetic (Fe, Co, Ni) nanoparticles from oxidization under conventional experimental conditions. Several techniques, such as carbon encapsulation, reagent stabilizing, and passivation of nanoparticles, have been developed to protect metallic particles. 

In an interesting variation of the technology. Law et al, (L2) described a liposome-based TSH assay in which the liposomal membrane surface contained covalently attached antibodies, and a modified membrane-impermeable acridinium ester derivative was encapsulated inside the vesicles. A normal sandwich assay was conducted using magnetic particles as the solid phase and antibody-sensitized liposomes as the label. The total assay time was 5 min, compared with the normal 2.5 hr, and showed superior sensitivity. 

The use of several techniques testing the magnetic response of particles ensembles on different time scales is desirable, especially when their size reaches the limit of resolution in TEM and their diffraction peaks are too broad for permitting the identification of all formed phases. The incorporation of Fe, Ni salts in TH permits to obtain metallic particles by ion irradiation or aimealing at low temperatures, simply in vacuum, while undesired phases are formed in TEOS (often even when heat treated in pure H2 atmosphere [9]). The formation of smaller particles, perfectly encapsulated in dense films of glass, under ion irradiation should permit to increase the areal density of information in magnetic memories. 

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