Effect of plasticizer on ionic transport and dielectric properties of PVA–H 3 PO 4 proton conducting polymeric electrolytes G.K. Prajapati, R. Roshan, P.N. Gupta n Physics Department, Banaras Hindu University, Varanasi, UP 221005, India article info Article history: Received 11 March 2010 Received in revised form 21 July 2010 Accepted 31 August 2010 Keywords: A. Thin films C. Differential scanning calorimetry (DSC) D. Electrical properties abstract Solid polymer electrolytes have attracted considerable attention due to their wide variety of electrochemical device applications. The present paper is focused on the effect of plasticizer to study the structural, electrical and dielectric properties of PVA–H 3 PO 4 complex polymer electrolytes. XRD results show that the crystallinity decreases due to addition of plasticizer up to particular amount of polyethylene glycol (PEG) and thereafter it increases. Consequently, there is an enhancement in the amorphicity of the samples responsible for process of ion transport. This characteristic behavior can be verified by the analysis of the differential scanning calorimetry results. FTIR spectroscopy has been used to characterize the structure of polymer and confirms the complexation of plasticizer with host polymeric matrix. Electrical and dielectric properties have been studied for different wt% of plasticizer and their variations have been observed. The addition of PEG has significantly improved the ionic conductivity. The optimum ionic conductivity value of the plasticized polymer electrolyte film of 30 wt% PEG has been achieved to be of the order of 10 4 S cm 1 at room temperature and corresponding ionic transference number is 0.98. The minimum activation energy is found to be 0.25 eV for optimum conductivity condition. & 2010 Elsevier Ltd. All rights reserved. 1. Introduction The development of new electrolyte materials for solid polymer electrolytes (SPE) and their application is creating opportunity for new types of electrochemical devices, which may themselves, in turn, revolutionize many industrial areas [1]. Solid polymer electrolytes have become the area of wide variety of fundamental and technological applications such as solid state batteries, fuel cells, double layer capacitors, sensors, electrochromic display devices, etc. [2–6]. The pioneering work of Wright et al. [4,7] and later Armand et al. [8] motivated researchers to work on SPEs due to their possible applications in various electrochemical devices. When polymers are complexed with host dopants like inorganic/organic acids/salts, they show appreciable change in their structural as well as electrical properties. However, these characteristics are not sufficient for application at ambient temperature due to low mobility of ionic charge carriers in the electrolytes. It is desirable to obtain films with high order electrical conductivity, which exhibit high fraction of amorphous phase due to addition of plasticizer into polymer matrix [9]. In the present report, polyvinyl alcohol (PVA) has been selected as a polymer matrix having hydrophilic properties, good transparency and fast charge transfer at electrode–electrolyte interface [10,11]. Considering these facts, thin films of PVA doped with H 3 PO 4 having PEG as a plasticizer have been prepared by well known solution cast technique. Here, an attempt has been made to investigate structural and electrical properties of plasticized polymer electrolytes with the help of B–G spectro- scopy, XRD, DSC and FTIR characterization. The effect of plasticizer has been discussed in terms of chain flexibility, enhanced amorphicity, polymer chain segmental motion and its dipole rotation. 2. Experimental 2.1. Thin film preparation PVA (average mol. wt. E1, 25,000 AR grade, Sd. Fine chem. make), PEG (mol. wt. E4,000 Sigma chem.) and H 3 PO 4 (88–93%, Ranbaxy Lab Ltd.) have been used as received. Thin films of pure PVA, PVA–H 3 PO 4 (70:30) and PVA–H 3 PO 4 –xPEG (x ¼ 10, 20, 30 and 40 wt%) have been prepared using triply distilled water as solvent by solution casting method. Details of thin film preparation have been discussed elsewhere [12]. Thin films, having thickness 50–100 mm are rinsed with benzene/methanol to remove impurities present on Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jpcs Journal of Physics and Chemistry of Solids 0022-3697/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2010.08.023 n Corresponding author. Tel.: + 91 0542 2570323. E-mail address: guptapn07@yahoo.co.in (P.N. Gupta). Journal of Physics and Chemistry of Solids 71 (2010) 1717–1723