Delivered by Ingenta to: Indian Association for the Cultivation of Science (IACS) IP : 202.54.54.240 Tue, 30 Oct 2012 18:45:19 ARTICLE Copyright © 2013 by American Scientific Publishers All rights reserved. Printed in the United States of America Advanced Science, Engineering and Medicine Vol. 5, pp. 126–132, 2013 (www.aspbs.com/asem) Ammonium Dihydrogen Phosphate/PVA Composite Films with High Dielectric Permittivity and Enhanced Thermal Stability Md Jamal Uddin 1 , Md G. Masud 1 , Arijit Ghosh 1 , T. R. Middya 2 , and B. K. Chaudhuri 1, * 1 Solid State Physics Department, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India 2 Department of Physics, Jadavpur University, Jadavpur, Kolkata 700032, India Transparent and anhydrous ammonium dihydrogen phosphate (NH 4 H 2 PO 4 or ADP) based polyvinyl alcohol (PVA) composite films of thickness 100 m have been prepared by solution casting technique. Several tech- niques like XRD, SEM, DSC, TGA and FTIR were used to characterize the prepared samples. The dielectric properties of the composites as a function of volume fraction of ADP, temperature, and frequency are studied in details. The dielectric permittivity decreases slowly with increasing frequency and gradually rises with increas- ing ADP contents in the composites. As the volume fraction of the ADP approaches percolation threshold, an abrupt increase in the dielectric permittivity occurs due to the formation of the conductive network in the matrix. The percolation theory, the microcapacitor model, and the simple concept of polarization in the capacitors are successfully employed to explain the experimental results. Thermal analysis of the composite films showed an increase in the glass transition temperature of the percolative polymer composite film, which confirms its enhanced thermal stability. KEYWORDS: Composites, Dielectric Properties, Filler, Film, Percolation, Thermal Stability. 1. INTRODUCTION Polymer-based composites with high dielectric permittiv- ity are important topics in the field of material science, and much attention has been paid in the past few years for various applications. 1–3 Polymers are selected as host materials for the energy storage applications on account of their intrinsic properties; such as good flexibility, easy processing, and cost effectiveness. 4 5 However, the dielec- tric permittivity () of many of the common polymers like, polyvinyl alcohol (PVA) is extraordinarily low (< 10). Thus, enhancement of  values of the polymer-based mate- rials, while maintaining their mechanical performance is necessary. Several important attempts have been made on ceramic–polymer composite (C/P) systems that adopt ceramics as fillers, e.g., BaTiO 3 , CaCuTi 4 O 12 , PZT, and PMN-PT. 6–10 However, these composites have relatively low dielectric permittivity (< 100) even at a high loading of ceramics (> 50 vol.%), and high loading also degrades the mechanical properties of the composites, such as flexi- bility and quality of the polymer composites. 11 12 To min- imize such problems of C/P, much effort has recently ∗ Author to whom correspondence should be addressed. Email: sspjamal@gmail.com Received: 14 May 2012 Revised/Accepted: 2 June 2012 been made to prepare inorganic filler/polymer compos- ite based on the percolation theory. 13 Dielectric permit- tivity of new polymer composites based on PVA such as graphene-PVA, 14 KDP-PVA, 15 poly(ethylene oxide)-PVA 16 have already been reported. But, the reported dielectric permittivity of such composite is moderately low (< 300 at 1 kHz) at room temperature. Recently, several stud- ies on transparent and solid proton conductor NH 4 H 2 PO doped PVA 17 and PVA/imidazole/NH 4 H 2 PO 4 . 18 Have been made for their use in solid electrochromic devices. Study of dielectric properties and percolative behavior of such system like NH 4 H 2 PO 4 /PVA composites are also important which have, however, not been yet reported. It is well known that ammonium dihydrogen phosphate (ADP) crystals are low cost and water soluble material. Therefore, if ADP is dispersed into polymer as a conduc- tive phase, much more microcapacitors could be formed, and the percolation would also be expected to appear at a suitable content of ADP, which subsequently could induce a high dielectric permittivity of the ADP/polymer composites. In this paper, we investigate ADP/PVA composites with low concentrations of ADP to significantly improve the dielectric permittivity of polymer matrix composites. This work focuses on frequency, temperature and concentration dependent dielectric behavior of the ADP/PVA composites 126 Adv. Sci. Eng. Med. 2013, Vol. 5, No. 2 2164-6627/2013/5/126/007 doi:10.1166/asem.2013.1241