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Multifunctional Nanocomposites Comprised of Magnetic Nanoparticles Grafted with pH and
Temperature Responsive Polymer
Swati Kumari*, Cayla Cook**, Evan Prehn*, Erick S. Vasquez***, Keisha B. Walters*
*Dave C. Swalm School of Chemical Engineering, Mississippi State University
**Department of Civil and Environmental Engineering, Mississippi State University
*** Department of Chemical and Materials Engineering, University of Dayton
Acknowledgments
This research was supported in part by the National Science Foundation (IIA-1430364, EPS-0903787, CBET-1403872). We appreciate I2AT at Mississippi State University for TEM imaging assistance.
Abstract
Stimuli responsive polymers (SRPs) have been of great interest in the last
few decades because of their potential in biomedical and environmental
applications. When SRPs are grafted from surface-modified magnetic-core
nanoparticles, they can be utilized for drug delivery and magnetic
resonance imaging. In this study, a one-step 3-
aminopropyltrimethoxysilane (APTS) hydrothermal approach was used to
synthesize APTS-coated iron oxide (Fe3O4@APTS) nanoparticles with
reactive surface amine groups. Using two successive surface initiated
atom transfer radical polymerizations (SI-ATRP), a pH and temperature
responsive block copolymer, poly-(itaconic acid)-b-poly(N-
isopropylacrylamide) (Fe3O4@PIA-b-PNIPAM) were grown from the
surface of Fe3O4@APTS. The nanocomposite consisting of a magnetic
nanoparticle (MNP) core and a polymer shell were characterized over a
range of temperature and pH using transmission electron microscopy
(TEM), light scattering, zeta potential, and Fourier transform infrared
spectroscopy (FTIR) to verify particle morphology, size distribution, charge,
and chemical composition. Results showed a successful synthesis, and
the resultant Fe3O4@PIA-b-PNIPAM demonstrated temperature and pH
responsiveness.
Introduction
Currently biomedical uses for magnetic nanoparticles includes drug
delivery, imaging and targeting [1]. Stimuli responsive polymers, or ‘smart’
polymers, can be grafted from MNPs via SI-ATRP to add polymers with
well-controlled molecular weight, chemical composition, and architecture
[2, 3]. Furthermore, PIA-b-NIPAM is of particular interest since it has
significant relevance for biomedical applications due to its lower critical
solubility temperature (LCST) of 32 °C [4], similar to human body
temperature. It’s potential has been highlighted in recent medical
applications [5].
Materials & Methods
Magnetic nanoparticles were synthesized through a hydrothermal reaction,
followed by a sequence of ATRP reactions to produce Fe3O4@PIA-b-
NIPAM , and characterized with:
 Transmission electron microscopy (TEM)
 Dynamic light scattering (DLS)
 Fourier transform infrared (FITR) spectroscopy.
Results and Discussion
References
Conclusions
 The structure, morphology, composition, and surface properties of
the formed particles were characterized by TEM, FTIR, and dynamic
light scattering measurements. A pH- and thermo-responsive block
copolymer comprised of PIA and PNIPAM was successfully
polymerized from the surface of nanoparticles.
 FTIR, TEM, and DLS was used to characterize the polymers and
showed that the modified MNPs were well dispersed and stable in
water as well as some organic solvents. In particular, these
thermoresponsive and pH responsive polymers can be used in smart
drug delivery and other biomedical applications that is guided by
external stimuli.
Experimental Scheme
 Fourier Transform Infrared Spectroscopy (FTIR)
❖ Transmission Electron Microscopy (TEM)
TEM image of (a) Fe3O4@APTS, (b) Fe3O4@APTS-PIA, and (c,d) Fe3O4@APTS-PIA-b-PNIPAM.
(a) The effective diameter of Fe3O4@APTS is ~300 nm. (b) The effective diameter of Fe3O4@APTS-
PIA more than doubles to ~800 nm. The grafted stimuli responsive polymer is visible around the
MNP. (c) Uniform nanocomposite size (narrow polydispersity) and effective diameter of the block
copolymer-modified ferrofluid/MNPs are shown. No nanoparticle agglomeration was observed. (d) A
magnified image of Fe3O4@APTS-PIA-b-PNIPAM shows an effective diameter of ~1000 nm (or ~1
micron).
❖ Dynamic Light Scattering (DLS)
DLS analysis was conducted on a dilute solution of approximately 1 μL of
Fe3O4@PIA-b-PNIPAM in a 3 mL solution with pH varying from 2 to 12.
Next, these samples were analyzed from 25 °C to 45 °C. DLS allows for
the measurement of the effective particle diameter and polydispersity.
At pH 12, pH 7, and pH 2—comprising the extreme and neutral pH values examined—all effective
diameters began < 600 nm. Previous DLS data denoted the effective hydrodynamic diameter at ~1100
nm; therefore, the PIA-b-PNIPAM coating was in a contracted state. Results show that at pH 10 the
polymer shell expands initially and then contracts at higher temperatures, matching the expected LCST
behavior.
0
200
400
600
800
1000
1200
1400
1600
25 27 29 31 33 35 37 39 41 43 45
EffectiveDiameter(nm)
Temperature (C)
pH 2
pH 4
pH 7
pH 10
pH 12
FTIR spectra of Fe3O4@APTS nanoparticles (blue spectrum) and Fe3O4@APTS-PIA-b-PNIPAM (red
spectrum). The white region indicates the regions for peaks assigned to hydroxyl, amine, alkane, and
carbonyl functional groups which matches the expected compositions of these SRP-MNP samples.
FTIR data characterizes the chemical functional groups present in the
sample using absorbance of infrared light.
TEM analysis allows for the visual interrogation of the samples on the
micro- to nano-scale in order to examine particle shape, polydispersity,
and other characteristics.
Sample Effective Hydrodynamic Diameter
Fe3O4@APTS 208.5 ± 2.7 nm
Fe3O4@PIA 880.9 ± 8.2 nm
Fe3O4@PIA-b-PNIPAM 1164.1 ± 63.1 nm
(a)
(d)(c)
(b)
NHO
( )n
COOH
COOH
( )n
Polymer and Surface
Engineering
Laboratory
(PolySEL)
http://www.polysel.che.msstate.edu//