الفهرس 
Theoretical BackgroundOnly 14 pages are availabe for public view
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Abstract
The increased indigence and miscellaneous applications of modern
electronic devices have resulted in competition for cost, reliability and
speed. This in turn has led to the search for new materials which can meet
the specific requirements. Polymer nanocomposites are among these
materials and have a number of technological applications, such as
telecommunications, optics industries, optical fibers, infrared sensors,
optoelectronic devices, and gas sensors.
The specific research objectives of this dissertation are preparation as
well as studying structural, thermal, optical, and dielectric properties of
PVC/SnO2 nanocomposites.
Chapter one:
This chapter explains the polymers, polymerization process and the
importance of poly (vinyl chloride) (PVC) which consider one of the major
thermoplastics with low production cost, as well as good insulation
performance, chemical and fire resistance, thermal stability and wide
energy gap so it is widely used in different fields of applications.
Additionally, the chapter showed the importance of the tin oxide
nanoparticles because it has high photocatalytic activity and storage
capacity used in many useful applications.
It also contained a survey of the various researches that included the
preparation, optical, thermal and the dielectric properties of the polymer
nanocomposites.
Chapter two:
That chapter contains the preparation of SnO2 nanoparticles with two
different sizes 50 nm and 15 nm and PVC/SnO2 nanocomposites with
different concentrations 2.0, 4.0 and 6.0 wt%.
The prepared PVC/SnO2 nanocomposites are characterized by X-ray
diffraction (XRD), scanning electron microscopy (SEM), Fouriertransform
infrared (FTIR) spectroscopy, Raman spectroscopy, Ultraviolet-
Visible (UV- VIS) spectroscopy, differential thermal analysis (DTA), and
dielectric spectroscopy.
Chapter three:
That chapter contains the analysis and discussion of different data.
XRD patterns of the PVC/SnO2 nanocomposites illustrated the amorphous
nature of PVC and its characteristic broad feature at 2θ~24°. The samples
doped with 2.0, 4.0, and 6.0 wt % SnO2 with two different sizes showed
the crystallization phase of SnO2. The average size of SnO2 nanoparticles
is calculated for two sizes by Scherrer’s formula (32.9 nm and 15.29 nm)
and W-H(UDM) method (43.86 nm and 16.57 nm). The values of strain
decreased as the SnO2 nanoparticle doping increased.
SEM images showed the morphology of PVC/SnO2 nanocomposites
films and the excellent dispersion of SnO2 nanoparticles on the polymer
surface is observed in the case of 50 nm of SnO2 nanoparticles, however,
in the case of 15 nm of SnO2 nanoparticles the agglomeration and
encapsulation of dopant nanofillers by the polymeric chain of PVC is
observed.
FTIR and Raman spectroscopy illustrated the characteristic peaks of
pure PVC and transmission intensity changed as the concentration and size
of SnO2 nanoparticles change that demonstrate the insertion and complexation between the dopant of SnO2 nanoparticles and polymeric
matrix of PVC polymer. Also, the Raman spectroscopy showed two peaks
at about 911 and 1030 cm-1, which are assigned to the Raman-active
vibrations of THF. Furthermore, the Raman peak at 350 cm-1 corresponds
to the surface phonon mode of SnO2 nanoparticles.
Optical absorption measurements showed that the transmission and
normalized absorbance decreased while the reflectance increased as the
addition of SnO2 concentration increased and size decreased. The direct
energy gap changed as the concentration of SnO2 increased from 5.04 eV
to 3.8 eV and from 5.04 eV to 4.4 eV for 50 nm and 15 nm of SnO2
nanoparticles. The indirect energy gap changed with the filler
concentration from 4.2 eV to 1.6 eV and 4.2 eV to 1.2 eV for 50 nm and
15 nm of SnO2 nanoparticles. Also, Urbach energy is increased as the
concentration and size of SnO2 decreased.
According to the Wemple and Didomenico (WDD) single oscillator
model the dispersion parameters were calculated. The values of Eo, Ed and
no for the PVC/SnO2 nanocomposites indicated that, as SnO2 nanoparticle
concentration increased, the Eo, Ed and no values increased for the
PVC/SnO2 nanocomposites. Additionally, as size of SnO2 nanoparticle
decreased the values of no increased and inversely Eo and Ed values
decreased. The incident optical spectrum moments M-1 and M-3 magnitudes
values increased with increasing SnO2 nanoparticle concentration.
Additionally, as the SnO2 nanoparticle size decreased the values of M-1
decreased and inversely the values of M-2 increased. Notably, as the SnO2
nanoparticle concentration increased, the plasma frequency ωp and real part
of the dielectric constant ℇ∞(1) values decreased. Also, as the SnO2
nanoparticle size decreased, the ωp and ℇ∞(1) values increased. The single
oscillator wavelength λo and the average oscillator strength So values for the PVC/SnO2 nanocomposites decreased as the SnO2 nanoparticle
concentration increased. Additionally, results showed that as the size of
SnO2 nanoparticle decreased the λo values is decreased and So values
increased for the PVC/SnO2 nanocomposites. The real and imaginary parts
of the dielectric constant increased with increasing addition of SnO2 in the
PVC/SnO2 nanocomposites, however, a hump in the curve was observed
for samples at energies between 4 to 5 eV. Additionally, as the size of SnO2
nanoparticle decreased the values of ℇ1 and ℇ2 increased. The optical
conductivity increased as the SnO2 nanoparticle content increased. The
optical conductivity increased with an increasing energy, and at energies
between 4 – 5 eV, a hump appeared in the curve. Additionally, at the visible
light energies range between 1.5 – 3 eV, as the size of SnO2 nanoparticle
decreased the optical conductivity increased. The obtained high optical
conductivity makes the present polymer nanocomposites suitable for the
fabrication of optoelectronic devices. The volume energy loss function
(VELF) values are always greater than the surface energy loss function
(SELF) values for all the samples. The VELF and SELF decreased as the
SnO2 nanoparticle concentration increased. However, for pure PVC, the
SELF at lower energy (1.5 – 4eV) is smaller than the values of the 2.0 wt
% and 4.0 wt % samples. Additionally, The VELF decreased and the SELF
increased as the size of SnO2 nanoparticle decreased.
The DTA analysis was confirmed, the enhancement of Tg after adding
SnO2 which could be attributed to the increase of amorphous region of
PVC matrix. The TGA curves of the PVC/SnO2 nanocomposites samples
have three stages of thermal degradation and thermal stability increased as
the concentration of SnO2 nanoparticles increased. The mass loss
decreased as the SnO2 concentration and size increased in the temperature
range of 350 to 500 ˚C, corresponding to increased thermal stability.
The dielectric spectroscopy showed that, the variation of the dielectric
permittivity against the frequency. The cole – cole model was applied and
the values of 𝜏𝜊 , ℇ𝑠, and ℇ∞ were determined.
The universal law was used to study the relation between the ac
conductivity and the frequency. The relation was represented by one
straight line at low temperature and at high temperatures was represented
by three regions depending on counter-ion model (CM). The values of
exponents, β and pre exponent were calculated to determine the conduction
mechanism.
Austin-Mott model was applied to study the relation of ac
conductivity σac(ω) with the density of states N(EF) at the Fermi level. The
variation of N(EF) at high temperature was observed. Also, based on the
Elliot model the ac conductivity σac(ω) is related to the concentration of
localized states N, the minimum binding energy Wm, and the minimum
hopping length, Rmin.