Nanoparticles surfaces colloidal stability

A major obstacle in making precise structures with metal colloids has been the control of aggregation and particle size distribution. The use of micelles has allotted some success in this regard with the formation of different metal colloid geometries [30]. It is known that the nanoparticles must be stabilized by organic molecules attached to their surface [31] and in general must be embedded in a solid matrix [32], This is done to prevent agglomeration and precipitation as... 

Reaction of the sandwich-type POM [(Fc(0H2)2)j(A-a-PW9034)2 9 with a colloidal suspension of silica/alumina nanopartides ((Si/A102)Cl) resulted in the production of a novel supported POM catalyst [146-148]. In this case, about 58 POM molecules per cationic silica/alumina nanoparticle were electrostatically stabilized on the surface. The aerobic oxidation of 2-chloroethyl ethyl sulfide (mustard simulant) to the corresponding harmless sulfoxide proceeded efficiently in the presence of the heterogeneous catalyst and the catalytic activity of the heterogeneous catalyst was much higher than that of the parent POM. In addition, this catalytic activity was much enhanced when binary cupric triflate and nitrate [Cu(OTf)2/Cu(N03)2 = 1.5] were also present [148],... 

Another aspect of this topic is the colloidal stability of nanoparticles, mainly in metal oxides. In water, the most common liquid medium, metal oxide surface chemistry is controlled by the surface hydroxyl groups [42-44]. The following surface equilibrium condition must therefore be considered ... 

Ferrofluids synthesized by chemical coprecipitation may be surfactant-stabilized ferrofluids or ionic ferrofluids. Surfactant ferrofluids are iron oxide nanoparticles coated by stabilizers or surfactant layer(s) for colloidal stability. The coating agents are polymers and surfactants, be they polar, non-polar or non-ionic. Fatty acid derivatives are most often used to stabilize these iron oxide nanoparticles either in organic or aqueous medium. If the particles are dispersed in an aqueous medium, a double layer of surfactant is needed to form a hydrophilic layer. On the other hand, if the particles are dispersed in an organic non-polar medium, one layer of surfactant forms a hydrophobic layer on the surface of the particles. 

Mori and Kawaguchi reported the preparation of magnetic polystyrene particles containing 30 wt% of magnetite. Magnetic polystyrene particles of 300 nm were produced and easily separated when persulphate, KPS or APS initiator was used. Conversely, due to high colloidal stability, the latex prepared by oil-soluble initiator (for instance AIBN) was not easy to separate, and the magnetite nanoparticles were located on the surface of the polystyrene latex. A mixture of initiators resulted in intermediate properties compared to individual systems [170]. 

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