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Magnetic Nanohybrids for Magnetic Resonance Imaging 121
Fig. 13. (a)–(d) Schematic mechanism of polystyrene/Fe 3 O 4 @SiO 2 magnetic Janus
nanohybrids (MJNHs), (e) TEM image of asymmetric Fe 3 O 4 /silica/polystyrene
nanocomposites particles, and (f) TEM images of MJNHs obtained without γ-Meth
acryloxypropyltrimethoxysilane molecules (scale bar is 500 nm and inset is 50 nm).
Reprinted with permission from Ref. 78.^
structure.^80 In the preparation method, they made hydrophobic iron
oxide nanoparticles about 10 nm in size and then asymmetric magnetic
composite particles were synthesized by mixing of the sol–gel reaction
with miniemulsion polymerization. Initially, a little fraction of styrene (St)
is changed into polystyrene chain and started to become heterogeneous
droplets at stage 3 by accumulating Fe 3 O 4 @TEOS on one side
and polystyrene on an opposite side. Finally, ammonia solution was added
to hydrolyze the TEOS to form SiO 2 shell as shown in TEM image
(Fig. 13(b)). Later, they repeated the same experiment without
γ-Methacryloxypropyltri-methoxysilane (MPS) and the result is shown in
Fig. 13(c). Therefore, MPS played an important character in the synthesis
of MNHs. Furthermore, these Janus hybrid particles showed superpara-
magnetic behavior due to their small sized iron oxide particles.
