Encapsulation, particle polymerization methods

Encapsulation of Solid Particles by the Concentrated Emulsion Polymerization Method [35]... 

Very fine solid particles, namely fumed silica, were also encapsulated via the concentrated emulsion polymerization method. The amounts of the components involved are listed under PLS1 in Table 21. The PLS1 capsules range in size from 1.0 to 1.5 pm. 

According to Hergeth and coworkers [55], a minimum surface of the inorganic particles is needed to prevent secondary nucleation. To estimate this amount, a formula was derived for seeded emulsion polymerization with spherical particles and a water-soluble initiator [55]. This formula was based on the observation that primary particles are produced by a coUapse and micellization process of oligomeric chains. An upper limit for the particle size was estimated to be 100 nm for the encapsulation of silica with polyvinyl acetate. A relatively water-soluble monomer is applied here for more hydrophobic monomers this upper limit will be higher. Because the surface area needed to prevent secondary nucleation is proportional to the monomer conversion per unit of time, the encapsulation efficiency can be improved by using monomer-starved conditions. So far, mainly submicrometer particles have been encapsulated with this method. The encapsulation of the larger filler particles... 

Interfacial polymerization techniques can be used to prepare robust microcapsules (about 4 pm) that have selectively incorporated functionality such as catalytic groups in their liquid-core domains. The synthesis of these particles is achieved via an oil-in-oil emulsion in combination with interfacial polymerization methods and allows for the encapsulation of substrates not compatible with water-in-oil or oil-in-water emulsion systems (Kobalija and McQuade, 2006). Often these capsules have polyurea shells that can be formed from w/o emulsions containing reactive polyols and isocyanates. This has been very elegantly demonstrated by McQuade and coworkers for the DMAP-catalyzed acylation transformation of an alcohol within the protected environment of polyurea microcapsules formed from reaction of a polyisocyanate and a poly(vinyl alcohol) in the presence of an amine catalyst (Price et ah, 2006 Poe et al, 2007). 

Other research groups reported the modification of the surfaces of iron oxides by hydrophilic macromolecules such as PVA and proteins. In this work, Lee et al. carried out a coprecipitation of iron salts in an aqueous solution of PVA to form a stabilized dispersion. They reported a decreasing crystallinity of iron oxide particles accompanying the increase of the concentrations of PVA, while the morphology and particles size remained unchanged. Other studied materials to encapsulate individual iron oxide nanoparticles or small clusters via polymerization methods involved natural polymers - or albumins. ... 

The extremely rapid fabrication method involves the mixing of two polymeric aqueous solutions. This direct method does not require any further purification. Neither organic solvents nor surfactants are required. The fabrication yield is above 95% and nanoparticle size ranges between 100 and 400 nm. Particles contain empty CyD moieties, which can entrap a variety of compounds depending on the stability constant of the resulting complex. Encapsulation is based on the same, simple, one-step procedure. 

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