Dielectric relaxation analysis and Ac conductivity of polyvinyl alcohol/polyacrylonitrile film
Introduction
Polyvinyl alcohol (PVA) is a semi-crystalline polymer, with a high solubility in water, low cost, non-toxicity, and flexible hydrophilic network. It has a high dielectric permittivity and good charge storage capacity. These properties make PVA is an important and interesting polymer [1], [2]. On the other hand, polyacrylonitrile (PAN), a synthetic vinyl homopolymer, offers quite good resistance [3], thermal stability [4], and mechanical strength [5]. It is regarded as the most preferable precursor material for the production of high strength, and high modulus carbon fibers. PAN fibers exhibit a high degree of molecular orientation, and higher melting point (Tm~317 to 330 °C) [6]. Moreover, PAN is completely non-toxic and suitable for biomedical applications [7], [8], [9], [10].
Incorporation of conducting polymer into another forming a blend, composite, or inter penetrated bulk network may lead to combine electrical conductivity with desirable physical properties of both two polymers [11], [12]. A treatment of polyaniline (PANI)/polyvinyl chloride (PVC) blend was examined [13]. The results of PANI/PVC blends showed an increase in conductivity at lower temperature.
knowing that the dielectric relaxation spectroscopy (DRS) is a useful method to throw light on the structure property relationships of polymers. Also, this method is sensitive to molecular fluctuation of dipoles within the dielectrics. These fluctuations are related to the molecular mobility of branched groups, segments or wholly polymer chains which show different relaxation processes. Moreover, the dipole motions within the amorphous and crystalline phases have an effect on the semi-crystalline polymers [14], [15]. Structural transitions in polymers are generally accompanied by changes in their relaxation properties. So, the relaxation properties are important for studying polymeric materials [16].
When an oscillatory electric field is applied to a polymeric material, several types of polarization are operative such as; electronic, ionic, orientational, or space charge. Orientational and space charge polarizations are particularly important when structural transitions are concerned. We reported previously on PVA/carboxymethyl cellulose (CMC) blends [17] as well as on 0.98 PVA/0.02 PANI film [18]. It become clear that the physical properties depend on the blend ratio of PVA and CMC. The physical properties of PVA are considerably affected by doping with PANI. Based on our knowledge, there is no previous report on the dielectric relaxation of PVA/PAN mixture. Therefore, we aimed in this work to throw light on the dielectric properties of (0.98/0.02) PVA/PAN film.
Section snippets
Experimental
PVA powder of molecular weight (Mw~17000 g/mol), and Polyacrylonitrile powder (Mw~150,000 g/mol) were obtained from (Polymer Laboratories, Essex, UK). (0.98/0.02) PVA/PAN film was prepared as follows: 0.98 g of the PVA and 0.2 g of PAN were dissolved separately each of them in 25 mL distilled water under stirring until clear solutions were obtained. The solutions were added to each other under ultrasonic stirring at room temperature (RT) for 2 h. The obtained mixture was then cast into Petri dishes
Dielectric permittivity
Fig. 1 depicts the frequency dependence of ε′ at different fixed temperatures. As seen, ε′ decreases with increasing of frequencies. The decrease in ε′ may be attributed to decreasing of the number of dipoles which contribute to polarization or the dipoles are no longer able to respond to the applied electric field. To emphasize the effect of PAN on the ε′ PVA, the inset of Fig. 1 shows the variation of ε′ of pure PVA and 0.98PVA/0.02PAN versus frequency at some selected temperatures. It is
Conclusions
The dielectric properties of 0.98 PVA/0.02 PAN film as a function of temperature and frequency were studied. The dielectric permittivity of PVA considerably increased by adding 0.02 wt% PAN. Different relaxation processes have been recognized. The first is ρ-relaxation due to space charge formation or Maxwell–Wagner polarization. The others are αa- and αc- relaxations that can be attributed to micro- Brownian motion of chain segments in amorphous and crystalline part of host PVA matrix,
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