Open Journal of Acoustics
2011. Vol.1, No.1, 9-14
Copyright © 2011 SciRes. DOI:10.4236/oja.2011.11002
Synthesis and Ultrasonic Characterization of Cu/PVP
Nanoparticles-Polymer Suspensions
Giridhar Mishra1, Satyendra Kumar Verma1, Devraj Singh2*,
Pramod Kumar Yadawa2, Raja Ram Yadav1
1Department of Physics, University of Allahabad, Allahabad, India;
2Department of Applied Sciences, Amity School of Engineering and Technology, New Delhi, India.
Received June 2nd, 2011; revised June 19th, 2011; accepted June 24th, 2011.
A polymer colloidal solution having dispersed nanoparticles of Cu metal has been developed using a novel
chemical method. Colloidal solutions of representative concentrations of 0.2 to 2.0 wt% Cu-nanoparticles con-
tents in the primary solutions were prepared to study the modified ultrasonic attenuation and ultrasonic velocity
in polyvinyl pyrrolidone (PVP) polymer molecules on incorporating the Cu-nanoparticles. The synthesized cop-
per metal nanoparticles dispersed in the polymer solutions were characterized by UV-Visible absorption spec-
troscopy, X-ray diffraction (XRD) and Transmission electron microscopy (TEM). The nanofluid sample showed
a symmetrical peak at 592 nm due to the surface plasmon resonance of the copper nanoparticles. XRD results
confirmed that copper nanoparticles were crystalline in the colloidal solution. The TEM micrograph revealed
spherical copper nanoparticles having diameter in the range 10 - 40 nm. A characteristic behaviour of the ultra-
sonic velocity and the attenuation are observed at the particular temperature/particle concentration. It reveals that
the colloidal suspension occurs in divided groups in the small micelles. The results are discussed in correlation
with the thermophysical properties predicting the enhanced thermal conductivity of the samples.
Keywords: Nanofluids, Colloids, Thermal Properties, Nanoparticles, Ultrasonic Properties
Nanoparticles with sizes in the nm range are used extensively
(Kota, 2007; Gatos, 2007; Cheng, 2008; Giraldo, 2008; Arribas,
2009; & Singh, 2009). Most of work on nanohybrids deals with
materials in the solid state. However, nanofluids are no less
interesting. Such fluids containing small amounts of metal (Cu,
Ag etc.) or nonmetal (SiC, Al2O3, TiO2, CuO etc.) nanoparticles
exhibit substantially enhanced thermal conductivity compared
to the base fluids. Therefore, nanofluids can be used as heat
transfer fluids; the thermal conductivity of the latter determines
the efficiency of heat exchange systems. Heat transfer fluids
with higher efficiency allow reduction of the sizes of heat ex-
change systems, thus miniaturization of devices. For example, a
small amount ( < 2wt%) of Cu nanoparticles or carbon nano-
tubes dispersed in ethylene glycol or petroleum increases the
inherently poor thermal conductivity of the liquid by 40% and
150% respectively. The thermal conductivity of nanofluid plays
an important role in the development of energy-efficient heat
transfer devices. However, the thermal conductivities of the
working fluids such as ethylene glycol, water, and engine oil
are relatively lower than those of solid particles. Therefore, the
development of advanced heat transfer fluids with higher ther-
mal conductivity is thus in a strong need now a days. The cen-
tury-old technique used to increase cooling rates is to disperse
millimetre or micrometer-sized particles in heat transfer fluids.
The major problem with suspensions containing millimeter or
micrometer-sized particles is the rapid settling of these particles.
Furthermore, such particles are not applicable to microsystems
because they can clog micro channels. Nanomaterials have
unique mechanical, optical electrical, magnetic and thermal
properties. Nanofluids (nanoparticles-fluid suspensions) are
engineered by suspending nanoparticles in traditional heat
transfer fluids such as water, oil, polymers and ethylene glycol.
A very small amount of guest nanoparticles, when dispersed
uniformly and suspended stably in host fluids, can provide
dramatic improvements in the thermal properties of host fluids.
More recently there has been an increasing interest in the
acoustical properties of suspensions for acoustic telemetry
through drilling fluids as well as arising demand for ultrasonic
particle size instrumentation. Commercial instrument have been
developed to characterize the properties of suspensions using
ultrasound (Kytömaa, 1995). Several scientists have made the
study of ultrasonic propagation behaviour through the suspen-
sion of solid particles particularly in micrometer or millimeter
size in a liquid aiming to identify the mechanism that enable
useful information to be extracted from the behaviour of ultra-
sonic properties, such as particle size, concentration and me-
chanical properties of the constituents (Biwa, 2004; Mbhele,
2003; Ensminger, 2005; & Shin, 2004). Polymers have been
found effective stabilizers of colloidal metal nanoparticles.
Recently, polymer nanofluids are the subject of considerable
interest because of the unique properties that can be achieved
with these materials. At the same time, because of their high
surface to volume ratio, nanoparticles suspended polymer ma-
trix significantly are revealing some new properties which are
not present in either of the pure materials. Therefore, the inves-
tigation of the influence of nanoparticles on the properties of a
polymer matrix is necessary in order to be able to better predict
the final properties of the complex fluids. In the present work
we have made the study of the ultrasonic attenuation and veloc-
ity in a polymer colloidal solution with dispersed Cu-metal
nanoparticles (nanofluid). We prepared stable nanofluids con-
taining copper metal nanoparticles suspended in the base fluid
polyvinyl pyrrolidone (PVP) and measured ultrasonic proper-
ties. Copper nanoparticles are of great interest because of their
use as coolant and its application in heat exchanger. The results
are analyzed and discussed in correlation with the microstruc-
ture and improved thermal properties of the complex nanofluid.
Experimental Details
Synthesis of Polymeric Nanofluids
CuCl2·2H2O and PVP were received from M/s Merck
Chemicals & Reagents. A freshly prepared homogeneous col-
ourless transparent PVP aqueous solution has been used. It was
obtained by dissolving 3.0 g PVP in 100 ml of double distilled
water. A continuous stirring over a magnetic stirrer at a con-
stant temperature of 25˚C - 30˚C promotes the PVP dissolution
in water in a clear solution. 1.0 M aqueous solution of
CuCl2·2H2O has been used to derive the nanofluids of Cu-PVP
having concentrations of Cu contents 0.2, 0.5, 1.0 and 2.0 wt%
in total solution using chemical route. The reactions were car-
ried out at room temperature (25˚C) with constant stirring over
a magnetic stirrer for 5 hours. These solutions were used as
stock solutions to perform the proposed ultrasonic velocity and
ultrasonic attenuation studies in Cu-PVP colloids.
Spectroscopy and Microscopy Me asurements
The absorption spectrum was recorded using a Lambda 35,
Perkin-Elmer double beam UV-visible absorption spectrometer.
A film of the nanofluid was dried on the glass plate for X-ray
diffraction analysis. XRD measurement was done by X’Pert-
Pro, PANalytical (with CuKα radiation λ = 1.5406 Å) operating
at room temperature. The particle size and its distribution were
analysed with E.M.-C.M.-12 (Philips) transmission electron
microscope operating at 200 KeV.
Ultrasonic Velocity and Ultrasonic Attenuation
Ultrasonic velocity measurements have been made at 2 MHz of
frequency with help of a variable path interferometer. Water is
circulated around the sample using a specific thermostat. The
measured value of ultrasonic velocity is accurate to 0.1%
with an error of measurement of 0.5˚C in temperature. The
ultrasonic attenuation (α/f2) measurements have been made by a
pulse-echo technique. The measured value of (α/f2) is accurate
to 2%. The standard liquids have been used to check the cali-
bration and accuracy of the measurements. Pulses are sent by a
5 MHz quartz crystal and the decay is observed on the cathode
ray oscillograph. The decay is made exponential by adjusting
the levelling screws and adjusting the crystal and the reflector
parallel to each other. The measured value of the temperature is
accurate to 0.5˚C as in the ultrasonic velocity measurements.
Results and Discussion
Physical Properties of Polymeric Colloids
When adding a CuCl2·2H2O solution (1.0 M) to a PVP solu-
tion (3.0 g/100ml) in water, a polymer complex forms by a
redox reaction of CuCl2·2H2O with the PVP molecules of re-
freshed reactive nascent surfaces caused during the processing
using the mechanochemical stirring under heating conditions of
the solution. The reaction occurs in steps, depending on the
initial concentrations in the two solutions and other experimen-
tal conditions. Ultimately, a colloidal solution consisting of Cu
metal nanoparticles embedded in a moiety of modified PVP
molecules appears in a colloid complex in a characteristic equi-
librium colour.
Figures 1 and 2 show the UV-visible spectrum of the copper
nanoparticles-polymer suspension having concentrations 0.2
and 0.5 wt% Cu nanoparticles in PVP. The UV-visible spec-
trum shows strong absorption peaks at 588 nm and 590 nm due
to the plasmon oscillation modes of conduction electrons in the
colloidal nanoparticles-liquid suspensions. This indicates that
size of Cu nanoparticles increases with increasing the concen-
tration. This prediction is confirmed by the TEM results of the
synthesized samples (Figures 3 - 5). The crystal structure of the
400 500 600 700 800 9001000
Absorbance (a.u.)
Wavelength (nm)
Figure 1.
UV-Visible spectrum of 0.2 wt% Cu nanoparticles-PVP suspension.
400 500 600 700 800 9001000
Absorbance (a.u.)
Wavelength (nm)
Figure 2.
UV-Visible spectrum of 0.5 wt% Cu nanoparticles-PVP suspension.
Figure 3.
TEM micrograph of 0.2 wt% Cu nanoparticles-PVP suspension.
Figure 4.
TEM micrograph of 0.5 wt% Cu nanoparticles-PVP suspension.
Figure 5.
TEM micrograph of 2.0 wt% Cu nanoparticles-PVP suspension.
Cu-nanoparticles dispersed in this polymer complex is exam-
ined with X-Ray diffraction. Figure 6 shows the XRD pattern
of the Cu naoparticles dispersed in PVP. All the peaks on the
XRD pattern can be indexed to that of pure Copper metal. The
peaks are corresponding to the 111, 200, 220 and 311 planes
respectively. The average crystalline size of the copper
nanoparticles was calculated to be 20 nm according to the half
width of the 111 diffraction peak using the Debye-Scherrer
formula. The Cu-nanoparticles occur in the usual cubic crystal
structure. TEM images of the Cu nanoparticles-polymer sus-
pensions with corresponding particles size distribution are
shown in Figures 4, 5 and 6 for three different concentrations.
The TEM images reveal that the Cu nanoparticles are spherical
in shape with sizes around 10 nm and clusters with size distri-
bution between 10 - 40 nm. The copper particles are well dis-
persed in colloidal solution as evidenced by TEM micrographs.
The corresponding selected area electron diffraction pattern is
displayed in the Figure 7 showing the crystalline structure of
Cu nanoparticles. It can be indexed to the reflection of
face-cantered cubic structure verifying the results obtained by
XRD pattern.
Figure 6.
XRD pattern of 0.5 wt% Cu nanoparticles-PVP suspension.
Figure 7.
SAED pattern of 0.5 wt% Cu nanoparticles-PVP suspension.
Ultrasonic Velocity and Ultrasonic Attenuation
As the ultrasonic velocity/attenuation is highly sensitive to the
local structure, we applied it here to examine its value in
Cu-PVP polymer colloids at various temperatures. The results
of the temperature dependent ultrasonic velocity and ultrasonic
attenuation are presented in Figures 7 and 8 respectively.
The results are showing the effect of Cu nanoparticles on the
ultrasonic velocity and attenuation. Figure 8 shows that the
ultrasonic velocity in Cu-PVP increases with temperature and
for higher temperatures it becomes constant. From Figure 9, we
find that maximum value of attenuation (
/f2) is at 25˚C in 0.2
wt% Cu-PVP polymer colloid sample. Also, there are charac-
teristic minima for different concentrations respectively. A
perusal of ultrasonic velocity and attenuation plots reveals that
the temperature dependency of the ultrasonic velocity and the
ultrasonic attenuation does not follow a linear curve. This
seems to be in contrary to the results in a sample of pure Cu
metal. In general, as in other materials (Mougin, 2003), both the
Figure 8.
Temperature dependent ultrasonic velocity in Cu-PVP nanofluids.
Figure 9.
Temperature dependent ultrasonic attenuation in Cu-PVP nanofluids.
ultrasonic velocity and the ultrasonic attenuation are quite sen-
sitive to the particles size, morphology and dispersion of the
particles. A macroscopic interaction of Cu nanoparticles with
the PVP molecules appears to be a critical parameter to control
their final values in this specific example of an inorganic-or-
ganic polymer nanocolloidal solution. The effective attenuation
in this example can be expressed as:
α = αp +αm + αpm (1)
where αp is the contribution from the Cu-metal, αm is the coun-
terpart contribution from the polymer matrix, αpm describes the
change in the final α-value owing to a macroscopic interaction
between the two components in a Cu-PVP nanocolloid struc-
ture and associated modified thermophysical properties of the
Biwa et al. (Biwa, 2004) analysed the ultrasonic attenuation
in millimeter sized particles-reinforced polymers by a differen-
tial scheme and found good agreement between the theory and
experiments. The wave attenuation in these composites is a
complex process where the viscoelastic loss and the scattering
loss coexist. It is also important to recognize that the relative
contributions of these loss mechanisms may change not only
depending on the acoustic properties of the constituent (matrix
and particles) but also according to the particle size, particle
concentration and the frequency of interest. In the differential
scheme, the changes of macroscopic properties of the complex
due to infinitesimal increase of particles concentration are given
in differential (incremental) forms. Thus the composite with the
particle volume fraction is regarded as a homogeneous effective
medium with the equivalent macroscopic properties given by
the Lame moduli λ and μ as well as the density (ρ). The com-
plex moduli λ and μ of an isotropic viscoelastic medium can be
given in terms of the ultrasonic velocities and ultrasonic at-
tenuation coefficients of longitudinal and shear waves. The
complete description of this theoretical model which we have
tried to apply is given in the literature (Biwa, 2004). The sig-
nificant attenuation due to scattering by the particles-reinforced
was incorporated in the total attenuation in their theoretical
model (Biwa, 2004). The observed attenuation in our case
could not be explained by the exact theoretical model following
the differential scheme. We found that the attenuation due to
scattering from the Cu-nanoparticles in the nanofluid is not
significant. It is also important to note that the characteristic
behaviour of the ultrasonic attenuation in the Cu + PVP
nano-colloids is not found in any of the individual components
of the composite (Abdul, 1982; & Awasthi, 2005). Calculated
value of the ultrasonic attenuation in the sample (0.2wt% of the
Cu nanoparticles) at 30˚C following the differential scheme
including the ultrasonic absorption due to nanoparticles and
thermo-elastic loss following the Mason scheme comes 85.54 ×
103 Np/cm. Here the thermal conductivity ‘K’ of the nanopar-
ticles for the calculation of thermo-elastic loss has been taken
following the molecular dynamics method. Here we incorpo-
rated the attenuation due to thermoelastic loss determined by
the formula αTh = ω2 <
> 2KT/(2ρ5
V). Here K is thermal
conductivity, ω(2πf) is frequency of the ultrasonic wave,
is Gruneisen number, T is the temperature in Kelvin scale, ρ is
the density, VL is the ultrasonic wave velocity. Here we have
not incorporated the thermal conductivity of complex thermoe-
lastic medium of our nanofluid as it is not known to us. As the
above formulations attenuation due to thermoelastic mechanism
is directly proportional to the thermal conductivity of the sam-
ples. The total observed attenuation in our experiment for the
sample is 101.76 × 103 Np/cm. At this juncture it is interesting
to investigate the source of excess ultrasonic attenuation.
Most importantly scientists have been perplexed by the
thermal phenomena behind the recently discovered nanofluids
like the present samples. One fascinating feature of nanofluids
like copper-ethylene glycol is that they have anomalously high
thermal conductivities at very low nanoparticles concentrations
(Hong, 2006; & Eastman, 2001). To date, the exact mechanism
of thermal transport in nanofluids is not fully known, and sev-
eral possible mechanisms based on theoretical models, experi-
ments and previous heat transfer theory have been suggested to
describe experimental results on thermal conductivity of nan-
ofluids. Brownian motion of suspended nanoparticles is attrib-
uted as one of the key factors of the greatly enhanced thermal
conductivity performance and it was not considered in conven-
tional thermal transport theory. Recently Philip et al. have con-
firmed the anomalous enhancement in the thermal conductivity
of the nanofluids of Au nanoparticles in PVA suspensions by
photoacoustic measurements (The work was presented in the
National Symposium on Ultrasonics, India in 2007). This en-
hancement is seen characteristic in nature at particular tem-
perature and particle concentration of the Au nanoparti-
cles-suspensions. The Brownian motion of nanoparticles at the
molecular and nanoscale level is considered as a key mecha-
nism governing the thermal behaviour of nanoparticles-fluid
suspensions (nanofluids). Eastman et al. proposed the theoreti-
cal model that accounts for the fundamental role of dynamic
nanoparticles in the nanofluids (Eastman, 2001). They have
derived a general expression for the thermal conductivity of
nanofluids involving different modes of energy transport in the
nanofluids. The important mode is thermal interaction of dy-
namic or dancing nanoparticles with base fluid molecules. Even
though the random motion of nanoparticles is zero when time
averaged, the vigorous and relentless interactions between liq-
uid molecules and nanoparticles at the molecular and nanoscale
level translate into conductions at the macroscopic level, be-
cause there is no bulk flow.
In FTIR results of Ag-nanoparticles-PVA, disappearance of
several bands (837, 711, 650 and 570 cm1) on increase in the
Ag-nano filler content in Ag-PVA suggests that the interaction
between Ag-nano particles and the matrix PVA molecule takes
place (Seok, 2004; Mbhele, 2003; Garcia-Serrano, 2004; &
Khanna, 2005). So on the basis of the FTIR results of Ag-PVA
we may say that there is interaction between Cu nanoparticles
and PVP molecules.
Thus we may postulate that the Brownian motion of the
Cu-nanoparticles in nanofluids produces convection like effects
at the nanoscale. Moreover, the thermal conductivity model not
only captures the concentration and temperature dependent
conductivity, but also predict strongly size-dependent conduc-
tivity. As we know, thermo-elastic ultrasonic attenuation is
directly proportional to the thermal conductivity of the compos-
ite and the attenuation due to scattering for the nanoparticles is
negligible. Therefore, we may predict that the effective in-
creased thermal conductivity of this nanofluid has such an im-
pressive effect as the excess attenuation on the total ultrasonic
attenuation behaviour. Thus, we have developed ultrasonic
mechanism to predict enhanced thermal conductivity due to
suspension of the metallic nanoparticles with very low concen-
tration into polymeric fluid. On the other hand the ultrasonic
velocity may be correlated to the viscoelastic property of the
complex fluid as follows:
If the polymer has sufficient molecular mobility due to
nanoparticles suspension, larger scale rearrangement of the
atoms may also be possible.
Since rate of conformational change α exp (E*/RT) (Ar-
henius-type expression), where E* is an apparent activation
energy of the process and R is gas constant (Fridley, 1989).
More technically the leathery behavior can be understood as
viscoelastic. Its response is a combination of viscous fluidity
and elastic solidity. The value of Tg is an important descriptor
of fluid thermomechanical response, and is a fundamental
measure of the materials propensity for mobility. The viscoe-
lastic response can be a source of substantial energy dissipation
during the nanoparticles dispersion. On the basis of the above
description correlating the behavior of temperature dependency
of the ultrasonic velocity, we may have the idea of the modified
glass transition temperature of the complex showing viscoelas-
tic behavior of the complex fluid.
We have successfully synthesized Cu-PVP nanofluids hav-
ing different concentrations of Cu metal nanoparticles in
ambient condition.
The UV-Visible spectra, XRD, TEM image and SAED
pattern confirm the formation of crystalline Cu nanoparti-
cles dispersed in PVP and also UV-Visible results are con-
sistent with TEM results.
The Brownian motion of the Cu-nanoparticles in nanofluids
produces convection like effects at the nanoscale.
On the basis of the behaviour of ultrasonic wave propaga-
tion we have developed ultrasonic mechanism to predict
enhanced thermal conductivity due to suspension of the
metallic nanoparticles with very low concentration into
polymeric fluid.
The authors are thankful to the Department of Science and
Technology, Govt. of India (DST project no. SR/S2/CMP-
0069/2006) for the financial support to carryout the work. We
are very grateful to Emeritus Prof. O.N. Srivastava-F.N.A.,
Department of Physics, Banaras Hindu University for his kind
permission for the XRD and TEM measurements in his labora-
tory. We are thankful to Prof. Ram Gopal, Department of
Physics, University of Allahabad for UV-visible facility and Mr.
Dinesh Jaiswal for his technical assistance in BHU, Varanasi.
Authors are also grateful to Dr. A.K. Tiwari (BSNVPGC,
Lucknow), Dr. Priyanka Awasthi (DMO, Lucknow), Dr. D.K.
Pandey (PPNPGC, Kanpur), Dr. Akhilesh Mishra (DST, New
Delhi), Dr. A.K. Gupta (NIOS, Noida), Dr. D.K. Singh (GIC,
Jalaun), Dr. A.K. Yadav (Ambedkar University, Lucknow), Mr.
Meher Waan (AU, Allahabad) and Mrs. Neera Bhutani (ASET)
for many useful helps like reading the manuscript, discussion
and knowledgeable suggestions during the preparation of the
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