Materials Sciences and Applicatio ns, 2011, 2, 111-115
doi:10.4236/msa.2011.22015 Published Online February 2011 (
Copyright © 2011 SciRes. MSA
Facile Synthesis of Polypyrrole/Titanate Core-Shell
Nanorods and Their Electrorheological
Jiexu Zhang1, Ying He2, Lijun Ji1
1College of Chemical Engineering, East China University of Science and Technology, Shanghai, China; 2Key Laboratory for Ul-
trafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and
Technology, Shanghai, China.
Received November 9th, 2010; revised January 14th, 2011; accepted January 24th, 2011.
In this work, polypyrrole (PPy)/titanate (TN) composite nanorods were successfully synthesized using cetyl trimethyl-
ammonium bromide (CTAB) as a structure-directing agent by in situ chemical oxidative polymerization. The structural
characterization indicated that the new composite rods were core (TN)-shell (PPy) nanostructure with the average di-
ameter in the range of 250-300 nm. Further, this semiconducting composite can be used as a dispersed phase in sili-
cone oil for a new electrorheological (ER) fluid, and its ER behavior was investigated under steady and oscillatory
shear. It was found that the PPy/TN fluid showed typical ER characteristics under an external electric field.
Keywords: Polypyrrole, Titanate Nanorods, Conducting Composite, Electrorheological Fluid, Viscoelastic Properties
1. Introduction
In recent years, considerable efforts have been made to-
wards the design and synthesis of one-dimensional (1D)
nanostructured materials (e.g. nanotube, nanowire and
nanorod) due to their potential applications in nanoscale
electronic and photonic devices, as well as in biotech-
nology. More recently, interesting ER properties induced
by 1D materials -based fluids have also attracted wide
attention [1-3].
As one of the important smart materials, ER fluids
have been intensively investigated over the past decades.
ER fluids are commonly known as suspensions consist-
ing of polarizable particles dispersed in an insulating
liquid medium [4]. Their rheological properties can rap-
idly and reversibly change upon application of an electric
field. This rapid and reversible electric-controlled me-
chanical response makes ER fluids to be used in the
automotive industry for clutch, brake and damping sys-
tems [5]. To facilitate the practical application of ER
technology, current research has focused on the devel-
opment of optimal anhydrous ER materials with high-
performance. Among these materials, 1D nanomaterials
have had the advantage of the ER materials with a good
ER efficiency due to their large aspect ratio (large in-
duced dipole moments) and good suspended stability. In
particular, 1D conducting nanocomposites, containing
inorganic nanotubes/nanowires coated with conducting
polymer, provide an exciting system exhibiting improved
chemical and physical properties over those of core or
shell materials [6]. Since conducting polymers (e.g.
polyaniline and polypyrrole) have been developed for ER
application in the past years because of their high po-
larizability, good thermal stability and controllable con-
ductivities and dielectric properties. Therefore, it is ex-
pected that 1D conducting nanocomposites with core-
shell structure could be used as advanced ER fluids.
In this paper, we present a facile way to prepare a new
conducting nanocomposite in which titanate (TN) rods
are encapsulated in the shell of polypyrrole (PPy). TiO2-
derived TN nanorods with wide band-gaps have also
recently received increasing interest due to their impor-
tant photocatalytic, photovoltaic, and semiconducting
properties [7]. Hydrothermal treatment of TiO2 precur-
sors in a highly alkaline medium is an effective way to
the synthesis of 1D TN nanostructures. The PPy/TN
composite nanorods were obtained by chemical oxidative
polymerization directed by CTAB in the presence of TN.
Facile Synthesis of Polypyrrole/Titanate Core-Shell Nanorods and Their Electrorheological Characteristics
The structure and morphology of the nanorods were
characterized. Furthermore, the potential application of
PPy/TN nanorods as an ER fluid under both steady and
dynamic shear is also investigated, which might be help-
ful in the design and fabrication of ER materials with
2. Experimental
2.1. Synthesis of PPy/TN Composite Nanorods
TN rods were prepared according to the report [8], with a
minor modification. In a typical synthesis, 1.5 of TiO2
powder (Degussa P25, Germany) was mixed with 70 ml
of 10 M NaOH solution, which was followed by hydro-
thermal treatment of the mixture at 200˚C in a 100 ml
Teflon-lined autoclave for 24 h. The white precipitate
was separated by filtration and washed with distilled wa-
ter until pH was around 7. The samples were then dried
in an oven at 60˚C for 12 h.
To obtain PPy/TN composite nanorods, 0.5g of TN
nanorods were dispersed in 50 ml of 0.1 M CTAB solu-
tion under ultrasonication at room temperature for 1 h.
After that, the mixture was cooled to 0-5˚C with vigorous
stirring. Then, a precooled solution of pyrrole monomer
was introduced into the above-mentioned solution. After
0.5 h, 50 ml of ammonium persulfate (APS) precooled
solution was added dropwise to the mixture (molar ratio
of Py/APS = 1), and the polymerization reaction was
allowed to proceed at 0-5˚C for 24 h. The resulting pre-
cipitate was filtered and washed with distilled water and
acetone. Finally, the product was dried in a vacuum oven
at 60˚C for 24 h.
2.2. Characterization of Materials
FT-IR spectra of the samples were obtained on Nicolet
Magna-550 spectrometer in the range of 4000-400 cm1,
the morphology of the nanocomposite was studied using
JEOL JSM-6360LV scanning electron microscope (SEM).
To prepare the ER fluid, PPy/TN particles were firstly
dedoped by immersion in 3 vol.% ammonia and then
dried in a vacuum oven at 60˚C for 12 h. The dried parti-
cles were dispersed in silicone oil (Fluid 200, Dow
Corning, UK; viscosity
c = 108 mPas, density dc =
0.965 g/cm3) to form the fluid concentration of 10 wt.%.
Measurements of rheological properties of the prepared
fluids were carried out under controlled shear rate (CSR)
mode using a coaxial cylinder viscometer (Bohlin
GEMINI, Malvern Instruments, UK). The suspensions
were placed in the Couette cell with the rotating inner
cylinder of 14 mm in diameter and the outer cylinder
separated by a 0.7 mm gap. They were connected to a
DC power supply producing the following field strength:
E = 0.5-3 kV/mm. All the experiments were carried out
at the temperature of 25˚C in the shear rate range 0.1-700
s1. Static yield stress was obtained from measurements
performed in CSS mode. Further, dynamic viscoelastic
tests were performed through dynamic strain sweeps and
frequency sweeps. The strain sweep was carried out with
applied strains of 104 to 1.0 at a frequency of 10 Hz un-
der an electric field in order to determine the linear vis-
coelastic region. The rheological parameters were then
obtained from the frequency sweep tests (0.1 to 50 Hz) at
fixed strain amplitude in the linear viscoelastic region.
3. Results and Discussion
3.1. Structure of Materials
The chemical structure of PPy/TN composite nanorods
was investigated using FT-IR spectroscopy. Figure 1
shows the IR spectra of the PPy and PPy/TN nanorods. It
is evident that the composite shows similar FT-IR char-
acteristic bands to those of polypyrrole in the 900-1600
cm1 range, i.e., 1550, 1460, 1300 and 1040 cm1 bands,
which are assigned to the pyrrole ring stretching, C–N
stretching mode, the in-plane vibrations of C–H, respec-
tively [9]. In addition, a broad band at 3430 cm1 is at-
tributed to the N–H stretching mode, and the bands at
1640 cm1 correspond to the bending mode of H–O–H.
On the other hand, other bands at 914 and 465 cm1 sug-
gest the occurrence of the TiO6 octahedra [10]. The
above results indicate that the as-synthesized composite
contain both PPy and TN components.
The morphologies of TN and PPy/TN nanorods char-
acterized by SEM are shown in Figure 2. The as-syn-
thesized TN nanorods with diameters of about 200 nm
and lengths of up to several micrometers are observed
(Figure 2(a)). In contrast to them, PPy/TN composite
exhibits larger diameter than that of TN, i.e. 250-300 nm.
PPy particles are almost deposited on the surface of TN
4000 3500 3000 2500 2000 1500 1000500
Transmitt ance ( %)
Wavenumber (cm-1)
1550 1460
Figure 1. FT-IR spectra of (a) PPy and (b) PPy/TN compos-
ite nanorods.
Copyright © 2011 SciRes. MSA
Facile Synthesis of Polypyrrole/Titanate Core-Shell Nanorods and Their Electrorheological Characteristics 113
Figure 2. SEM images of (a) TN nanorods and (b) PPy/TN
composite nanorods.
nanorods to form a core-shell structure shown in Figure
2(b). Also, the aspect ratios of PPy/TN nanorods are es-
timated to be 10-15.
3.2. ER Behavior of PPy/TN Fluid
This new core-shell nanocomposite can be used for ER
application. Figure 3 provides the flow curve for PPy/
TN based ER fluid measured in CSR mode under four
different electric field strengths. Without an electric field,
the suspension shows a slight departure from Newtonian
fluid behavior due to the relatively high particle concen-
tration. When an electric field is applied to the suspen-
sion, the shear stress increases quickly with electric field,
and yield stresses appear like in a Bingham fluid, which
is the typical rheological characteristic of ER fluid under
an electric field [11]. The figure also shows that, in the
low-shear-rate region the shear stress slightly decreases
with increasing shear rate up to a critical shear rate, and
Shear stress (Pa)
Shear rate (s-1)
0.0 kV/mm
1.0 kV/mm
2.0 kV/mm
3.0 kV/mm
Figure 3. Shear stress versus shear rate for PPy/TN-based
fluid under different electric field strengths.
then increases with shear rate. The critical shear rate is a
transition point at which the fluid starts to exhibit
pseudo-Newtonian behavior. This phenomenon is related
to the structural change of ER fluid under shear. The
dispersed particles are polarized and formed chain-like
structures as a result of electrostatic forces generated
between the dipoles induced by the external electric field.
In the low-shear-rate region, with increasing shear rate
the slight decrease of shear stress is a consequence of the
destruction rate of chain-like structures exceeding their
reformation rate. In the high-shear-rate region, the shear
stress increases with shear rate showing pseudo-Newto-
nian, implying that the hydrodynamic forces rather than
the electrostatic forces begins to dominate the flow be-
havior. This is similar to other reports [12,13]. Further,
one can note that the critical shear rate shifts to high
value with increasing electric fields, which is related to
the magnitude of attractive interactions between the dis-
persed particles.
The change of the microstructure of PPy/TN compos-
ite fluid can also be detected under dynamic shear. Fig-
ure 4(a) shows the storage modulus (G) and loss mo-
dulus (G) as a function of strain for 10 wt.% PPy/TN
fluid. It can be found that both moduli increase with in-
creasing electric field strength and G is larger than G in
the linear viscoelastic range. This is mainly caused by the
elasticity of PPy/TN based fluid. The chain-like struc-
tures formed by the polarized PPy/TN particles become
more elastic and stiffer at higher electric field, which
makes the fluid behave like solid, resulting in a larger G.
When the strain is increased, for example, exceeds the
critical strain, the chain-like structures will collapse and
the fluid shows liquid behavior, i.e. G > G. Figure 4(b)
presents G and G of PPy/TN fluid as a function of fre-
quency at a small strain of 2 ×10–4 in the linear viscoelas-
Copyright © 2011 SciRes. MSA
Facile Synthesis of Polypyrrole/Titanate Core-Shell Nanorods and Their Electrorheological Characteristics
Copyright © 2011 SciRes. MSA
(a) (b)
Figure 4. G and G as a function of strain amplitude (a) and (b) frequency for PPy/TN fluid under different electric field
strengths: open symbols for G; shaded symbols for G.
tic range. At the same electric field strength, both moduli
are almost independent of frequency in the low fre-
quency range due to rigid chain-like structure, while with
increasing frequency they increase with frequency show-
ing a transition to a nonlinear region because of the onset
of chain rupture [14,15].
4. Conclusions
A new polypyrrole/titanate composite nanorod was syn-
thesized via chemical oxidative polymerization of pyr-
role directed by cetyl trimethylammonium bromide in the
presence of titanate nanorods. FTIR and SEM charac-
terization confirmed that polypyrrole was deposited on
the surface of titanate particles and formed a core-shell
structure. Further, it was observed that the suspension of
polypyrrole/titanate exhibited typical ER behavior under
an external electric field. Shear stress and dynamic
moduli increase with electric field due to elasticity of the
ER fluid. And in the linear viscoelastic range, storage
modulus is larger than loss modulus under an electric
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