Biomedical Engineering Reference
In-Depth Information
actively employed as effi cient stabilizers for the controlled synthesis of cobalt
nanoparticles. The as-synthesized polymer nanocomposites consisting of inor-
ganic nanoparticles and organic polymers, often exhibit a host of mechanical,
electrical, optical and magnetic properties, which are far superior to those of the
individual components. These desirable properties are derived from a synergistic
and hybrid interaction between the inorganic and organic interfaces that separate
the building blocks. Many reviews have been produced describing the role of
polymer stabilizers and polymer-supported magnetic nanocomposites [44].
Currently, the
in situ
synthesis of cobalt nanostructures in polymer matrix has
been widely utilized, where the polymer material and cobalt source are mixed in
solution, after which a reducing agent is added to reduce the cobalt ions to metallic
cobalt. A seminal study reported the synthesis of well-defi ned cobalt colloids by
using random poly(methyl methacrylate- ethyl acrylate -
N
- vinyl - pyrrolidone) ter-
polymers as stabilizers, with Co
2
CO
8
being decomposed in refl uxing toluene and
the particle size readily controlled by varying the cobalt to surfactant loading ratio
[45]. Subsequently, a variety of polymers with functional groups such as -COOH,
- NH
2
and - SO
3
H have been used to produce polymer-supported cobalt nano-
composites. As an example, a perfl uorinated sulfo - cation membrane (MF - 4SK),
prepared using an ion-exchange method, was used to create superparamagnetic,
self-aggregated cobalt nanoparticles, the magnetic properties of which indicated
that such nanoparticles exhibited superparamagnetic properties above the block-
ing temperature (
T
B
) [46]. Most recently, water-soluble cobalt spherical nanopar-
ticles and nanorods have been produced using alkyl thioether end-functionalized
poly(methacrylic acid) as ligands, where the dispersion was stable for approxi-
mately two months and could, potentially, be used for biomolecular conjugation
due to its carboxylic functional groups [47]. Polymers spheres such as polystyrene
were used as sacrifi cial templates for other air-stable cobalt nanoparticles where,
through a single-step swelling process, the cobalt precursors diffused into uni-
form polystyrene microspheres, followed by a decomposition of the polymer-
encapsulated metal complexes under an inert atmosphere at 600 ° C. Ultimately,
the carbon and metal oxide formed a thin shell which protected the core of the
cobalt nanoparticles against further oxidation [48].
Pyun and coworkers have recently prepared phosphine oxide and amine-
functionalized styrenic polymers, and used these as surfactants to mediate the
growth of ferromagnetic cobalt nanoparticles [49]. The polymer moiety was capable
of encapsulating the nanoparticle to form a shell, and of imparting long-term col-
loidal stability to the magnetic dispersions in solution, such that the 1-D structure
of the assembled nanoparticles could be formed in the solid state. In addition,
functionalized cobalt nanoparticles have been used as the macroinitiators for
surface-initiated polymerizations when preparing magnetic polymer brush shells
with an adjustable thickness [50].
Most recently, polyvinyl pyrrolidone (PVP) has been demonstrated as one of
the most effective stabilizers and modifi ers to prevent the agglomeration of
metal nanoparticles, and to provide an elaborate control of the growth of metal
nanocrystals in chemical solution synthesis, such as Ag [51] , Au [52] , Pd [53] , and
