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The effect of magnesium oxide nanoparticles on the optical and dielectric properties of (PVA-PAA-PVP) blend.

INTRODUCTION

In recent years, polymer nanocomposites and understanding their chemical and physical properties have attracted great attention. The presence of nanoparticles in polymer improves the optical, mechanical and electrical properties of the materials; metal oxide nanoparticles doped polymer materials have been studied as alternative materials for optical applications such as microoptical elements and planar waveguide devices.

Many polymers have been proved to be suitable matrices in the development of composite material structures due to light weight, resistance to corrosive environment, good adhesion with reinforcing elements, and in some cases ductile mechanical performance [1]. Low cost polymer dielectric capacitors and low weight play a key role in electrical energy storage applications including portable mobile electronic devices, pulse power devices, stationary power systems and hybrid electric vehicles. Currently, neither ceramics nor polymers can reach the requirements of the growing need for faster discharge rate capacitors and high gravimetric energy. Hence, finding novel materials or systems with the aforementioned properties is essential. One way of making these systems will be combining superior mechanical properties of polymer material with the excellent dielectric properties of metal oxide. These materials will be especially useful in pulse power devices for a variety of military and commercial applications. Ceramic polymer nanocomposites are typically formed by introducing inorganic metal oxide nanoparticles fillers into a polymer matrix. Due to their size and concomitant surface tension effects, nanoparticles often agglomerate in polymer matrices [2]. Nanocomposites on base of semiconductor nanoparticles and polymer matrix are prospective materials for application in optoelectronics, sensor electronics and for creation of luminescent materials..etc. Introducing semiconductor nanoparticles into polymer matrials volume changes physicochemical properties of the system. The properties of the obtained structures depend on a semiconductor particle type, dimensions of particles. Furthermore, the physicochemical properties of the nanocomposite will be under influence of the effects of interaction of nanoparticles with polymer, interphase phenomena in polymer-nanoparticle nanocomposite[3]. Optical properties of polymers very important in study of electronic transition of polymer material and the possibility of polymers application as a cover in solar collection, optical filters, green house and selection surfaces. The information of the electronic structure for amorphous and crystalline semiconductors has been mostly accumulated from the studies of optical properties in wide wavelength range [4]. Poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP) and are included in the list of synthetic polymers which are used in medicine. PVP has a good reputation due to its outstanding absorption and complexes abilities, whereas PVA presents important features such as recognized biodegradability, high hydrophilicity, biocompatibility and good processability on film formation [5].

MATERIALS AND METHODS

Polyvinyl alcohol- poly-acrylic acid- polyvinyl pyrrolidinone- magnesium oxide nanoparticles nanocomposites re prepared by using casting method. The pure blend prepared with different weight percentages of polymers are (90 wt.% of polyvinyl alcohol, 4wt.% of poly-acrylic acid- 6 wt.% of polyvinyl pyrrolidinone. The magnesium oxide nanoparticles was added to polymers blend with different concentrations are (0, 1.5, 3, 4.5) wt.%. The optical properties of (PVA-PAA-PVP-MgO) nanocomposites measured by using the device UV/1800/ spectrophotometer in wavelength range (200-800) nm. The dielectric properties of (PVAPAA-PVP-MgO) nanocomposites were measured using LCR meter in the frequency(f) range100Hz-5MHz at room temperature.

RESULTS AND DISCUSSION

The absorbance spectra of (PVA-PAA-PVP-MgO) nanocomposites with wavelength range (200-800) nm is represented in Fig.1. As shown in the figure, the absorbance of blend increases with the increase of the magnesium oxide nanoparticles concentration. The increase of the absorbance due to the increase of charge carriers in the nanocomposite [6].

The effect of magnesium oxide nanoparticles on the absorption coefficient of (PVA-PAA-PVP-MgO) nanocomposites is shown in Fig.2. The absorption coefficient (a) is defined as the ability of a nanocomposite to absorb the incident light of a given wavelength [[alpha]=2.303A/t, where A: is the absorbance , t: the sample thickness in cm]. The figure shows that the absorption coefficient of (PVA-PAA-PVP-MgO) nanocomposites is increased with the increasing of the magnesium oxide nanoparticles weight percentages. The increase of absorption coefficient with concentration of magnesium oxide nanoparticles attributed to the increase the absorbance of the light [7].

From the Fig. 2, the values of absorption coefficient of (PVA-PAA-PVP-MgO) nanocomposites is less than [10.sup.4] [cm.sup.-1], this mean the (PVA-PAA-PVP-MgO) nanocomposites have indirect energy gap as shown in Fig. 3 and Fig.4. The energy band gap is calculated by the relation: [alpha]h[upsilon] = c[(h[upsilon] - [E.sub.g]).sup.r] where h[upsilon] is the photon energy, c is a constant, [E.sub.g] is the optical energy band gap, r=2, or 3 for indirect allowed and indirect forbidden transition. The energy band gap of the (PVA-PAA-PVP-MgO) nanocomposites decreases with increasing of the magnesium oxide nanoparticles weight percentages which related to the increase of the local level in forbidden energy gap[8].

Fig. 5: shows the variation of extinction coefficient (K=[alpha][lambda]/4[pi]) of (PVA-PAA-PVP-MgO) nanocomposites with the wavelength for different concentrations of magnesium oxide nanoparticles. The extinction coefficient is increased with increasing of the magnesium oxide nanoparticles weight percentages, this increase of extinction coefficient attributed to loss of energy for incident light because the reaction between the incident light and the molecules of the nanocomposite [9].

Fig.6: shows the variation of refractive index (n= (1+[R.sup.1/2])/ (1-[R.sup.1/2])) of (PVA-PAA-PVP-MgO) nanocomposites and incident photon energy. The refractive index of (PVA-PAA-PVP-MgO) nanocomposites is increased with the increase of the magnesium oxide nanoparticles weight percentages, this is due to the increase of scattering of the light [10].

Fig.7 and Fig.8 show the variation of the real part (:[[epsilon].sub.1] =[n.sup.2]-[k.sup.2]) and imaginary part ([[epsilon].sup.2] =2nk) of dielectric constant for (PVA-PAA-PVP-MgO) nanocomposites with wavelength for different concentrations of magnesium oxide nanoparticles. The real and imaginary parts of dielectric constant of (PVA-PAA-PVP-MgO) nanocomposites are increased with increasing of the concentrations of magnesium oxide nanoparticles; This increase of parts of dielectric constant attributed to the increase of the absorption and scattering of incident light [11].

Fig.9 shows the variation of the dielectric constant ([[epsilon].sup.-] = [C.sub.p]/[C.sub.o] where: [C.sub.p] is parallel capacitance and [C.sub.o] is vacuum capacitor). of (PVA-PAA-PVP-MgO) nanocomposites with the frequency of applied field. The dielectric constant of (PVA-PAA-PVP-MgO) nanocomposites is decreased with the increase of frequency, this behavior due to the space charge polarization which is decreased to the total polarization where this type of polarization becomes the more contributing at low frequencies The dielectric constant of nanocomposites increases with the increase of concentrations of the magnesium oxide nanoparticles, this is due to the increase the dipoles charge [12], as shown in Fig. 10.

The variation of dielectric loss ([??] = [??]D where D is loss factor) of (PVA-PAA-PVP-MgO) nanocomposites with the frequency is shown in Fig. 11. From the figure, the dielectric loss of nanocomposites decreases with the increase of the frequency which attributed to the decrease of the space charge polarization contribution. The dielectric loss of (PVA-PAA-PVP-MgO) nanocomposites increases with increasing of the concentration of nanoparticles; the increase of dielectric loss with increase of nanoparticles weight percentages due to the increase of the charge carriers [13], as shown in Fig. 12.

Fig. 13: shows the variation of A.C electrical conductivity ([[sigma].sub.A.C] = w [epsilon]" [[epsilon].sub.0] where [[epsilon].sub.o] is Vacuum permittivity) of (PVA-PAA-PVP-MgO) nanocomposites as a function of the frequency. The figure shows that the electrical conductivity is increased with the increase of the frequency which attributed to the polarization effect and hopping. The A.C electrical conductivity is increased with the increasing of concentration of the magnesium oxide nanoparticles, this is related to the hopping of charge carrier conduction mechanism [14], as shown in Fig.14.

Conclusions

1--The optical absorbance for (PVA-PAA-PVP-MgO) nanocomposites was increased with the increase of the magnesium oxide nanoparticles weight percentages.

2--The optical constants for (PVA-PAA-PVP-MgO) nanocomposites were increasing with the increase of the magnesium oxide nanoparticles weight percentages.

3--The energy band gap for (PVA-PAA-PVP-MgO) nanocomposites was increased with the increase of the concentrations of the magnesium oxide nanoparticles.

4--The dielectric constant of (PVA-PAA-PVP-MgO) nanocomposites was decreased with the increase of the frequency and it increases with the increase of the weight percentages of magnesium oxide nanoparticles.

5--The dielectric loss of (PVA-PAA-PVP-MgO) nanocomposites was decreased with the increase of the frequency and it increases with the increase of the weight percentages of magnesium oxide nanoparticles.

6--The A.C electrical conductivity of (PVA-PAA-PVP-MgO) nanocomposites increases with the increase of the concentration of magnesium oxide nanoparticles and frequency.

ARTICLE INFO

Article history:

Received 19 January 2015

Accepted 18 February 2015

Available online 28 February 2015

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(1) Ibrahim R.Agool, (2) Firas S. Mohammed and (3) Ahmed Hashim

(1,2) Al- Mustansiriah University, College of Science, Department of Physics, Iraq

(3) Babylon University, College of Education of Pure Science, Department of Physics, Iraq

Corresponding Author: Ibrahim R.Agool, Al- Mustansiriah University, College of Science, Department of Physics, Iraq E- mail: ahmed_taay@yahoo.com
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Author:Agool, Ibrahim R.; Mohammed, Firas S.; Hashim, Ahmed
Publication:Advances in Environmental Biology
Article Type:Report
Date:Jun 1, 2015
Words:1958
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