Magnetoresponsive hybrid microgels: close packed magnetite nanoparticles core - double layer
polymeric shells with anionic or cationic functionalities
Rodica Turcu1, Izabell Craciunescu1, Vlad Socoliuc2 , Anca Petran1, Camelia Daia2, Ladislau Vekas2
1 National
Institute R&D for Isotopic and Molecular Technologies, 65-103 Donath Street, 400293 ClujNapoca, Romania
2
Romanian Academy-Timisoara Branch, Center for Fundamental and Advanced Technical Research,
Lab. Magnetic Fluids, Timisoara, Romania
rodica.turcu@itim-cj.ro
Abstract
Magnetic nanoparticles (MNPs) well separated or in clusters, with proper surface functionalization
usually dispersed in liquid carriers or embedded/encapsulated in polymeric networks, are the basic
building blocks of a large variety of multifunctional carriers. The encapsulation of magnetic nanoparticles
into polymeric micro/nanogel systems gives rise to hybrid magnetic carriers that combine the features of
a polymeric gel with the interesting properties of magnetic nanoparticles and make them suitable for
applications such as magnetically targeted drug delivery, hyperthermia treatments, magnetic resonance
imaging contrast enhancement, magnetic carriers in bioseparation equipments [1-2].
We report the synthesis and characterization of magnetic microgels based on controlled clustering of
hydrophobic magnetite nanoparticles and coating with different polymeric shells of poly(Nisopropylacrylamide), polyacrylic acid, poly(3-acrylamidopropyl)-trimethylammonium chloride.
The oil in water miniemulsion method [3] was applied for the preparation of magnetic nanoparticles
clusters (NPCs) using toluene based magnetic nanofluid (MF) containing Fe3O4 nanoparticles stabilized
with a hydrophobic layer of oleic acid. The MF was added to the aqueous solution containing sodium
dodecyl sulphate (SDS) as surfactant and treated ultrasonically to obtain small stable droplets with
NPCs. The as prepared magnetic miniemulsion was heated to remove the toluene and then was
carefully washed several times with methanol-water mixture, magnetically separated and redispersed in
water. Stable aqueous dispersions of magnetic nanoparticles clusters coated with the surfactant SDS
were used for encapsulation into polymers. Magnetic microgels with cation exchange (CEX) or anion
exchange (AEX) functionalities have been obtained by coating the NPCs with two polymer shells using
layer by layer free radical polymerization of either N-isopropylacrylamide and acrylic acid (M-NIPA-AAc)
or N-isopropylacrylamide and 3-acrylamidopropyl)-trimethylammonium chloride (M-NIPA-APTAC) in the
presence of the crosslinker N,N-methylene bis-acrylamide and oxidant ammonium persulfate.
The TEM image of NPCs coated with SDS, figure 1 shows that magnetite nanoparticles stabilized with
oleic acid are densely packed into spherical clusters coated with SDS with sizes in the range 100-500
nm. Dynamic light scattering and zeta potential measurements of the microgels gives values of the
mean hydrodynamic diameter, Dh in the range 517-914 nm and zeta potential values between -23mV
and -37mV for CEX microgels and between +35 mV and +39 mV for AEX microgels. The magnetization
vs. applied magnetic field at room temperature for NPCs stabilized with SDS and for magnetic microgels
shows superparamagnetic behavior, the saturation magnetization has relatively high values in the range
46-56 emu/g, figure 2.
The chemical surface analysis of magnetic nanoparticle clusters and magnetic microgels was performed
by X-ray Photoelectron spectroscopy (XPS). The coating of NPCs stabilized with SDS with double layer
of polymers poly(N-isopropyl acrylamide) and polyacrylic acid is evidenced by the characteristic peaks
in XPS spectra: (i) amide group N-C=O (286 eV) in C1s spectrum, NH (399 eV) in N1s spectrum, C=O
(532.5 eV) in O1s spectrum, which are specific for pNIPA; (ii) carboxyl group O-C=O in C1s and O1s
spectrum, specific for pAAc. XPS spectra of AEX magnetic microgel, confirm the double layer polymer
coating of SDS stabilized NPCs with poly(N-isopropyl acrylamide) and poly(3-Acryloamido-propyl
trimethylammonium chloride), figure 3.
The CEX and AEX magnetic microgels exhibit good stability, high saturation magnetization/large
magnetic moment, response to moderate magnetic fields, being promising materials for applications in
high gradient magnetic separation and nanomedicine.
References
[1] Y. Lu, M. Ballauff, Progress in Polymer Science, 36 (2011) 767-792.
[2] N.S. Satarkar, D. Biswal, J.Z. Hilt, Soft Matter, 6 (2010) 2364-2371.
[3] P. Qiu, C. Jensen, N. Charity, R. Towner, C. Mao, J. AM. CHEM. SOC. 132 (2010) 17724–17732
Acknowledgements
Support by the European project FP7 No. 229335 MAGPRO²LIFE and the Romanian project
83EU/2010 is acknowledged.
Figures
60
50
40
M (emu/g)
30
20
10
0
-10
-20
-30
NPCs
M-NIPA-AAc
M-NIPA-APTAC
-40
-50
-60
-1000 -800 -600 -400 -200
200 nm
Figure 1. TEM images of NPCs stabilized with
SDS prepared by oil in water miniemulsion
method
0
200 400 600 800 1000
H (kA/m)
Figure 2. Magnetization curves at room
temperature for NPCs and magnetic microgels
M-NIPA-AAc (CEX), M-NIPA-APTAC (AEX).
4
9.0x10
C 1s
C-C, C-Hn
O 1s
5
2x10
C=O
Intensity (c.p.s.)
Intensity (c.p.s.)
4
6.0x10
C-N, C-O
N-C=O
4
3.0x10
Fe-O
In-O (support)
5
1x10
0.0
OSO3
0
294
292
290
288
286
284
282
280
540
538
536
Binding energy (eV)
534
532
530
528
526
524
Binding energy (eV)
2
9.0x10
NH
N 1s
4
S 2p
1.0x10
Intensity (c.p.s.)
Intensity (c.p.s.)
2
+
N
3
5.0x10
S 2p1/2
6.0x10
2
3.0x10
0.0
0.0
408
S 2p3/2
406
404
402
400
398
Binding energy (eV)
396
394
174
172
170
168
166
164
Binding energy (eV)
Figure 3. High resolution XPS spectra for C1s, O1s, N1s, S2p, core levels from AEX microgel MNIPA-APTAC obtained by coating of SDS stabilized NPCs with poly(N-isopropyl acrylamide) and
poly(3-Acryloamido-propyl trimethylammonium chloride).