AC Conductivity and Conduction Mechanism of Iron (II) Chloride (FeCl2) /Poly (vinyl alcohol) (PVA)/Poly (vinylpyrroldone) (PVP) Polymer Blend Electrolyte

Blend sample based on Poly (vinyl alcohol) (PVA)/Poly (vinylpyrroldone) (PVP), (50:50), and their blend electrolyte with different weigh ratio of Iron (II) Chloride (FeCl 2 ), (0.5, 1 and 2 wt.%), have been prepared using casting method. The AC electrical properties of these samples were investigated in the frequency range 1 kHz to 1 MHz and in temperature ranging from 30 to 150 °C. The real and imaginary impedance, frequency and temperature dependence, indicate the enhancement of the electrical conductivity of the blend due to addition of FeCl 2 . Pure and electrolyte blend samples were found to be characterized by a plateau region at low frequency and high temperature, and this plateau region increases with increase in temperature and /or FeCl 2 weight ratio. Nyquist plots for pure and blend electrolyte samples presented depressed semicircles at all temperatures. For pure blend sample, the ac conductivity was attributed to hopping mechanism while for blend electrolyte sample ionic conduction represents the predominant conduction mechanism. Jonscher universal power law was used to study the conduction mechanism for pure and electrolyte blend sample. The activation energy for blend and blend electrolyte samples was calculated and two activation regions were appeared for blend electrolyte samples. increases which indicates the active participation of the ionic conductivity through the samples. For pure blend sample, the AC conductivity was attributed to hopping mechanism. The results for blend electrolyte samples was interpreted based on the increase of chain mobility due to thermal activation and the contribution of ionic conduction. Jonscher universal power law was used to study the conduction mechanism for pure and electrolyte blend sample. The activation energy for blend and blend electrolyte samples was calculated and two activation regions were appeared for blend electrolyte samples.


Introduction
The characteristics of PVP depend on its molecular weight. PVP is available in several grads (molecular weights) and it is soluble in aqueous organic solvent in addition to its nontoxic character, all these characteristics give PVP great exibility for several applications. PVP was used as adhesive agent for improving the strength of paper in paper manufacture and also in painting industry and ink, imaging, lithography and other industries [1,2]. In medical applications [3,4], PVP has been used as a blood plasma expander for trauma victims [5]. It can also be used as a binder in many pharmaceutical industries [6,7], as it is easily absorbed into the body, making it gain great importance in the eld of pharmacology. PVP also was used as a pore forming agent to enhance the polymeric water lter membrane [8] and its addition can affect the quality of the resulting ultra ltration polymeric membrane.
Poly(vinyl alcohol) (PVA) represent one of the famous polymer which has a wide range of applications such as packing, biomedical and medical applications [9][10][11]. It has some natural characterization such as non-toxicity, chemical resistance biocompatibility and hydrophilicity. Beside these characteristics, PVA is a good member for preparation of several kinds of polymer blends and polymer electrolytes. PVA is water soluble polymer and it was used in several kind of water ltration researches [12,13]. Both polymers PVA and PVP has excellent wetting properties and readily forms lms, which makes it good as a coating or an additive to coatings.
The eld of polymer blend and polymer blend composite represent one of the advanced area for research in polymer physics and this due to its contribution in several types of applications [14]. Two or more polymers can be used to prepare a new blending of polymeric material with unique and interesting properties, different from those in the original components [15] .
Since PVP and PVA possess an interesting set of dipolar groups [25], the formation of polymer blend electrolyte based on such polymer blend will be interesting for the scientists and researchers. The dielectric relaxation spectroscopy (DRS) may be a suitable method for investigating the properties of such electrolytic polymer blende in a wide range of frequency and temperature [26]. Dielectric relaxation spectroscopy is a useful technique to investigate the relaxation behavior of polymeric electrolyte.

Composite Characterization
The polymer blend composite samples were characterized by FT-IR, and AC spectroscopy. FTIR spectra for PVA/PVP blend and FeCl 2 electrolyte samples were recorded using Perkin Elmer spectrum 400.
Dielectric measurements were carried out using Keithley Instruments 4200 Semiconductor Characterization System over a frequency range 1 kHz to 1 MHz and temperature range from room temperature up to 150 °C.
The spectrum of FeCl 2 /PVA/PVP showed peaks at a similar wavenumber to that of the polymer blend PVA/PVP, suggesting that FeCl 2 did not affect the structural characteristics of blend. However, a change in the relative intensity of certain bands (2922 cm -1 ) in the spectrum of the 1wt.% FeCl 2 sample. This peak is become sharper and a clear peak at 2853 cm -1 was obtained. This can be attributed to the hydrogen bonding between the blend and FeCl 2 (see Figure 2).

Impedance Spectroscopy
One of the most important techniques for detecting the dielectric relaxation processes in polymer, polymer blend and polymer composite is the impedance spectroscopy. The analysis of complex impedance represents a powerful tool to investigates and distinguish between different components which may contributes in the material. From the complex impedance analysis and the expected equivalent circuit based on its data, we can get more deep information about the physical process that takes place inside the material under test. Pure blend sample (PVA/PVP) does not show any signi cant dependence on temperature for either the behavior of the real part (Z') or the imaginary part (Z'') of impedance. This behavior can be ascribed to the dielectric nature of the blend sample, and thus the behavior is closer to the capacitive behavior over the used frequency range. The motion of the main chain due to thermal activation is small and it adds a slight change in the impedance behavior.
It is clear that, blend electrolyte samples have different behavior than pure sample. At low temperatures, the behavior has a tendency to to that of the capacitive reactance and the relationship between impedance and frequency is linear relation. This can be attributed to the incapability of the dipoles to oriented or respond to the applied frequency. The frequency-independent plateau region increases with temperature and it is connected with the dc-conductivity of the polymer blend electrolytes (see Figures  4(a), 5(a) and 6(a)). In the high frequency region, the capacitive component of real part of impedance was predominating and the dependence become linear. As the concentration of FeCl 2 increases, the high frequency dispersion (Z'') is shifted towards the higher frequency side, and the conductivity was found to be increased (see for temperature higher than 50 °C, the semicircles were followed by spikes at lower frequency side which increase with increasing salt weight ratio and temperature. These results indicates a non-Debye relaxation nature (a single relaxation time) for pure and electrolyte blend samples [29]. The equivalent circuit which represents such depressed semicircle plot comprising a constant phase element capacitor (CPE) in parallel with a resistor. This combination was connected in series with another constant phase capacitive element to represent the shape of the spike at low frequency region [30]. Figure 11 shows the effect of FeCl 2 weight ratio (concentration) and temperature on Nyquist plots. It was noted that increasing the temperature and /or FeCl 2 weight ratio reduces the diameter of the semicircle, which indicates the active participation of the ionic conductivity through the samples. AC conductivity behavior of all blend electrolyte samples is characterized by plateau region (frequencyindependent) at higher temperature. This plateau become more predominated for higher weight ration doped samples (2 wt.%).

AC conductivity
For low frequency region, σ ac for blend electrolyte samples was frequency independent especially at temperature higher than 50 °C. This can be interpreted due to the ionic conduction which dominates the ac-conductivity that arises as a result of the response of the polymer chains and dipoles to applied frequencies. For pure blend sample, it was notice that the dependence of the ac-conductivity on frequency continue up to 80 or 90 °C, and the ac-conductivity increases due to hopping mechanism which increase with frequency increases [31,32]. and 2 wt.% FeCl 2 electrolyte blend samples respectively. It is obvious from these set of gures that the acconductivity was thermally activated and the mobility of charge carrier and charge density increase with temperature increases. The main chain and segmental chain motion play an important role for the conductivity behavior for pure and electrolyte samples [32].
The addition of electrolyte to polymer or polymer blend can form complexes with the polymeric chains, which impede the movement of the chains and makes them require higher energy to contribute to the acelectrical conductivity, and the ionic conductivity has the advantage in the active participation of the acelectrical conductivity. Occasionally, at small concentrations of salt, the uid can act as a plasticizer and facilitate the movement of the polymeric chains. From the table it was note that the electrolyte blend samples have two linear regions, the rst at low temperatures in which the contribution return to polymer with activation energy in the range 0.13 to 0.19 eV (greater than pure blend) which indicates a complex formation between some chains and the ionic liquid. The activation energy for second region (ionic conduction contribution) was ranging between 0.2 to 0.43 eV. The activation energy was decrease with increasing of salt concentration. Jonscher universal power law can be used to analyses the overall behavior of AC conductivity based on the following equation [33,34]: where σ(ω), σ dc , A, ω and n are de ned as the total conductivity, dc-conductivity, constant, angular frequency and an exponent factor. The dependence of log σ vs. log f in the high temperature region and the dependence of exponent n on temperature are illustrated in Figures 16 and 17 for pure blend and blend electrolyte samples respectively. The exponent values n was determined by knowing the slope of log σ vs. log f relation and are summarized in tables 2 to 5.
It was noticed that the values of the exponent n varies with salt concentration [35,36]. Also, pure sample has two regions follows the power law which are depend on the frequency range. The change of n with concentrations was attributed to the change of the interface between different constituents of the samples. In the case of polymer blend electrolyte, the host was a polymeric blend beside a reminder of the individual polymers (partial miscibility) which were not contributed in the blend process. At this hypothetical region, one can imagine that three contributors are present, the blend electrolyte, the electrolyte solution (reminder) and the immiscible reminder of PVA and PVP polymers electrolytes.
It was also noted that the behavior of the exponent n with the temperature for pure blend sample is linear whether at temperatures below or higher than glass transition point. At higher temperatures (see Figure  (16-b)), two linear regions were detected and n was linearly depend on temperature. Whereas, for electrolyte samples the behavior of n(T) follows the exponential function (n decreases exponentially with temperature) [37]. This means that the movement of chains and side chain may be activated due to addition of electrolyte (FeCl 2 ). This will excites the movement of ions signi cantly and increase the conductivity reducing the effect of interfacial regions which increase the probability of hopping mechanism for ions [38]. Also, according to Correlated barrier hopping model (CBH), as temperature increase the ionic hopping between sites to overcome the potential barrier will increase [37,39,40].
The following tables ( Table 2 to 5) illustrates the values of the exponent n, the coe cient A, and the dcconductivity (σ dc ) for pure sample at different temperatures. It is obvious that the increase in the dcconductivity was accompanied by a decrease in the value of n and thus the expansion of the plateau region at the expense of the exponential region of σ(f) [36].
These results con rm the role of thermal activation of the main chains beside the side chains which are contribute signi cantly to the electrical conductivity. It is clear that the role of chain, movement due to thermal activation, was greater than the role of the applied alternating voltage. The presence of two regions for pure blend sample, (Figure (16)) at high temperatures, may be attributed to the presence of more than one conduction mechanism beside the possibility of contribution of polymer reminders side by side to polymer blend.

Conclusion
This work investigated the study of some electrical properties of a polymeric blend composed of PVA and PVP as well as a polymer blend electrolyte by adding FeCl2 with different weight ratios (0.5, 1 and 2 wt.%). Impedance analysis was carried out in the frequency range from 1 kHz to 1 MHz under different temperatures (30 to 150°C). The incorporation of FeCl2 in the blend matrix enhanced the electrical conductivity of the blend and the ac-conductivity increase as the FeCl 2 weight ratio increases. Nyquist plots for pure and blend electrolyte samples presented depressed semicircles at all temperatures. Pure samples did not show a complete semicircle shape due to the insulating nature of the blend and the inability of the charge carriers to move except at high temperature.
Nyquist plots diameter reduced as the temperature and /or FeCl 2 weight ratio increases which indicates the active participation of the ionic conductivity through the samples. For pure blend sample, the AC conductivity was attributed to hopping mechanism. The results for blend electrolyte samples was interpreted based on the increase of chain mobility due to thermal activation and the contribution of ionic conduction. Jonscher universal power law was used to study the conduction mechanism for pure and electrolyte blend sample. The activation energy for blend and blend electrolyte samples was calculated and two activation regions were appeared for blend electrolyte samples.