Supporting Information
Asymmetric Iron Oxide Nanoparticles Assemblies
by Phase Inversion
Yihui Xie, Rachid Sougrat and Suzana P. Nunes*
Figure S1. FT-IR spectra of (a) pristine MNPs, (b) oleic acid and (c) OA coated MNPs
Figure S1 displays the FT-IR spectra of the pristine Fe3O4 (a), pure oleic acid (b) and
Fe3O4 nanoparticles coated with OA(c). In (a), three bands at 572, 1624 and 3386 cm-1
can be observed from spectrum of pristine Fe3O4 nanoparticles. The broad band with a
maximum at 572 cm-1 corresponds to the vibration of the Fe–O bonds in the crystalline
lattice of Fe3O4. The presence of this characteristic peak indicates that the MNPs were
synthesized successfully by co-precipitating an aqueous Fe3+/Fe2+ solution.1 The
characteristic bands of hydroxyl groups, 1624 and 3386 cm-1, also appear in the spectrum
of pristine MNPs because during preparation in an aqueous environment, their surfaces
were readily covered with hydroxyl groups.2 In the curve of oleic acid, two sharp bands at
2926 and 2855 cm-1 are attributed to the asymmetric CH2 stretch and the symmetric CH2
stretch, respectively. The intense peak at 1712 cm-1 is derived from the existence of the
C=O stretch and the band at 1286 cm-1 exhibits the presence of the C–O stretch. The O–H
in-plane and out-of-plane bands appeared at 1466 and 939 cm-1, respectively.3 Compared
with the pristine MNPs, besides the characteristic bands of Fe–O bonds and hydroxyl
groups still exist in the spectrum of OA coated MNPs (see Figure S1 (c)), a few new
absorption bands appear after the oleic acid coating. It can be seen that the absorption
peaks at 2922 cm−1 and 2852 cm−1 represent the stretching vibration of C–H bond in the
OA chain coated on the nanoparticles. These two bands shifted to a lower frequency
region than that of pure oleic acid, which indicates that the hydrocarbon chains in the
monolayer surrounding the nanoparticles were in a closed-packed, crystalline state.4 The
C=O stretch band of the carboxyl group in oleic acid, present at 1712 cm-1 in the
spectrum of the liquid oleic acid, is absent in the spectrum of OA-MNPs. Instead, there
are two new bands at 1534 and 1406 cm-1, which are related to the asymmetric COO– and
symmetric COO– vibration, and an adsorption band at 1068 cm-1 arises from C–O single
bond stretching.
Figure S2. TGA curves of (a) pristine MNPs, (b) OA-MNPs, (c) NH2-MNPs, (d) Br-MNPs,
(e) PS-MNPs, (f) pure PS
Figure S3. FT-IR spectra of (a) OA-MNPs, (b) APTES, (c) NH2-MNPs, (d) BiBB, and (e) BrMNPs
In Figure S3 (a), the characteristic bands of Fe–O bonds at 568 cm-1 and hydroxyl
groups at 1628 and 3421 cm-1 exist in the spectrum of OA-MNPs. After the oleic acid
coating, it can be seen that the absorption peaks at 2922 cm−1 and 2852 cm−1 represent the
stretching vibration of C–H bond in the OA chain, two new bands at 1534 and 1406 cm-1,
which are related to the asymmetric COO– and symmetric COO– vibration, and an
adsorption band at 1068 cm-1 arises from C–O single bond stretching. It can be seen from
Figure S3 (b) that three strong peaks at 1123 cm−1, 1050 cm−1 and 961 cm−1belong to Si–
O–Si vibration from free liquid APTES, and two peaks at 3354 cm−1 and 1640 cm−1
contribute to N–H stretching vibration and NH2 bending, respectively. Two bands at 2932
cm−1 and 2891 cm−1 can be assigned to the C–H stretching vibration of propyl group in
APTES. The silica network is adsorbed on the magnetite surface by Fe–O–Si bonds. But
this adsorption band cannot be seen in the FTIR spectrum because it appears at around
584 cm−1 and therefore overlaps with the Fe–O vibration of magnetite nanoparticles.5 So,
the introduction of APTES to the surface of MNPs can be confirmed by the bands at 930
cm−1 assigned to the Si–O–Si groups (see Figure S3 (c)). It is worth to note that
compared with that of OA coated MNPs (at 572 cm–1), the characteristic absorption
bands of the Fe–O bond of APTES coated Fe3O4 shift to higher wavenumbers of 584 cm–
1
. The explanation is that Fe–O–H groups on the surface of the Fe3O4 particles were
replaced by Fe–O–Si(O–)2–R. Higher electronegativity of –Si(O–)2– than H leads to the
enhancement of bond force constant for Fe–O bonds, so that the absorption bands shift to
higher wavenumbers.6 Figure S3 (e) shows the FT-IR spectrum of Br-MNPs in
comparison with those of NH2-MNPs (Figure S3 (c)) and BiBB (Figure S3 (d)).
According to the spectra, the strong band at 1767 cm–1 which belongs to Br–C=O
stretching from BiBB is replaced by a new band at 1646–1 representing N–C=O group on
the magnetite nanoparticle surface.7 This result confirms that the reaction between the
anchored amino group on the nanoparticle surface and BiBB was successful with the
formation of N–C=O group and bromide group has been immobilized to obtain BrMNPs.
Figure S4. GPC traces of (a) free polystyrene and (b) cleaved polystyrene chains
Figure S5. FT-IR spectra of (a) polystyrene coated Fe3O4 nanoparticles, (b) pure PS
The spectrum of polystyrene coated MNPs (Figure S5 (a)) displays bands at 3025
cm-1 and 1601 cm-1 corresponding to the C–H asymmetric stretching and C=C stretching
of aromatic ring, respectively. The peak at 2920 cm-1 is attributed to C–H asymmetric
aliphatic stretching of the carbon chain backbone. The characteristic peaks at 1654–1942
cm-1, 756 and 696 cm-1 attests to the phenyl group in polystyrene. Figure S5 (b) shows
that the FT-IR spectroscopy of PS-MNPs agrees with the as-prepared pure polystyrene
perfectly. The Fe–O bond observed in the previous modification steps is absent in the
spectrum of PS-MNPs, which confirms that the iron oxide core was encapsulated by thick
polymer shell.
Figure S6. TEM image of pristine iron oxide nanoparticles
(a)
(b)
(c)
(d)
Figure S7. TEM images of (a, b) NH2 -MNPs in toluene and (c, d) Br-MNPs in toluene
(a)
D=30.5 nm
PDI=0.14
(b)
D=18.9 nm
PDI=0.14
Figure S8. Hydrodynamic size distribution of (a) NH2-MNPs and (b) Br-MNPs in toluene,
determined by dynamic light scattering.
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