Study Effect KPF6 Salt and TiO2 Nanocomposite on the Characteristics of PVP Polymer Electrolyte

INTRODUCTION
In general Polymer materials are the materials of the new era have important properties as light weight, low cost and easy processibilty. These polymeric materials can be used as a polymer electrolyte in rechargeable batteries or solid state devices [1], in super capacitors [2], smart windows [3], gas sensors [4], etc. The polymer can be blended with another polymer or a dopant so as to improve its properties. Studies on optical properties of these polymers have attracted much attention in different application in optical and electronic devices [5, 6]. Adding the materials as doping to polymers leads to change and improves their optical properties by charge transport of doped polymer electrolyte films [7].
The polymer poly vinyl pyrrolidone (PVP) is soluble in water and other solvents, Chemical formula was (C6H9NO)n ,  melting point equal to 150oC and the density is 1.2 g/cm3. It is a light flaky hygroscopic as a dry powder, readily absorbing up to 40% of its weight in atmospheric water. In solution, can be used it as a coating or an additive to coatings because of it has excellent wetting properties and readily forms films [8]. The electrical properties of polymer PVP can be improved with the incorporation of cupric sulphate (CuSO), as it has the capacity to significantly modify the electrical and optical properties of a material. The ionic nature of CuSO causes it to dissociate into Cu2+, and SO2- ions in aqueous solution and these ions are responsible for the conductivity of the host polymer [9].
The aim of project was study the effect of KPF6 salt and TiO2 nanomaterials on the polymer PVP as thin films polymers. This study was represented by determine TGA analysis and the energy gap from the optical properties for thin films polymers.

MATERIALS AND METHODS
The electrolyte solution of polymer PVP were prepared by dissolving PVP with each of KPF6 and TiO2 in distal water for different weight ratio (0, 10, 20) %.  This solution was mixing using hotplate stirrer for 120 min with 600rpm at room temperature. After that thin film for different weight ratio was then prepared on glass substrate (1.5 X 2.5) cm2 by cast Solution method and put at room temperature for (24 h.) to get polymerized homogeneous solid films of doped polymer PVP. The solid thin films were put on hot plate for 30 min to do annealing for it at 70oC. To measure thickness of the films was that by using (digital thickness gauge meter) where the films put on the stainless steel substrate, table 1 describe the weight ratio with thickness for all types of thin films. The optical measurements were recorded at room temperature using (T80-uv/vis. Spectrophotometer) in wavelength range from (300-800) nm

RESULTS AND DISCUSSION
Thermal gravimetric analysis (TGA)
A thermal gravimetric analysis of polymer thin films of PVP/KPF6, PVP/TiO2 and PVP/KPF6-TiO2 were done by Perkin Elmer (TGA4000) under nitrogen atmosphere, 20ml/min gas flow rate and 20OC/min. In this case TGA is a useful analytical technique to asses thermal stability of materials thin films by recording weight loss of a sample as a function of temperature [10, 11]. Fig. 1 show TGA thermogram of polymers thin films, from Fig. 1 we see that PVP undergoes two decomposition steps ,the first occurs at temperature range of  (40-165.38)OC with weight loss of 6.997% that represents the loss of residual solvent and low molecular weight oligomers. The second decomposition step occurs at temperature range of (463 – 522.09) OC with weight loss of 80.668% that represents the decomposition of PVP.   Also for all thin films can be insert the effect KPF6 and TiO2 on polymer PVP in table 2, If we compared between PVP and all films that containing on KPF6 and TiO2 for different weight ratio we see that the weight loss was decreases with increase of weight ratio for added KPF6 but it’s don’t effect with increase TiO2 nanocomposite.
  
Optical Properties
The Absorption spectra of thin films at the range wave number (300-800) nm were studies using spectrophotometer type (T80 UV/Vis Spectrometer).  Fig. 2 show the relationship between the Absorption spectra as a function of the wavelength for PVP after adding KPF6 salt and TiO2 nanocomposite for it. From Fig.2a we see that decreases in the absorption spectra with increase wavelength for all ratios, but its increases with increase the ratio of KPF6 from (0.008) at the wavelength (354) nm to (0.076) at the wavelength (442) nm. And when replaced  KPF6 with TiO2 nanocomposite as Fig. 2b, we get on better result represented by increases in the absorption spectra with increase weight ratio of added, the maximum absorption was (0.838) at the wavelength (556)nm. The materials can be crystalline and amorphous and having energy band gap (BG) that can be determined using the optical absorption spectrum. The electrons will be excited from the VB to the CB by the absorption spectrum to tackle the nature and quantification of the energy (BG). In this case the absorption coefficient (α) can be determined using the relation [12, 13]:
                   
                                                          

Where: d is the film thickness and A is the optical Absorbance. 
Fig. 3 represent the relationship between Log(α) as a function of energy, The  data of  absorption coefficient lead to obtain on the energy band gap which is depend on the theory of Bardeen et all[14]:

Where, r is equal to (1/2, 2/3, 2 or 3) and ,Eg, is the optical energy band gap.  The plot of (αhν)2 versus the energy (photon energy) are shown in Fig. 4, from figure we determine the energy gap by intercept with x-axis and its increases with increase the weight ratio each of KPF6 and TiO2 nanocomposite (Table 3). From table we see that the added of TiO2 nanocomposite to polymer PVP was better than added KPF6 salt as thin films that clear in value of the energy gap.  

CONCLUSION
For study TGA, If we compared between PVP and all films that containing on KPF6 and TiO2 for different weight ratio we see that the weight loss was decreases with increase of weight ratio for added KPF6 but it’s don’t effect with increase TiO2 nanocomposite. For study Absorption spectra, we see that the best result was for added TiO2 nanocomposite to polymer PVP if we compared it with KPF6 salt, where the maximum absorption was (0.838) for added TiO2 nanocomposite but for added KPF6 salt the absorption value was (0.076).

CONFLICT OF INTEREST
The authors declare that there are no conflicts of interest regarding the publication of this manuscript.