%0 Journal Article
%T Study of Dielectric Relaxation Behavior of Liquid Crystal Copolyester Vectra-A by Thermally Stimulated Discharge Current Technique
%A Sapna Kalia
%A J. K. Sharma
%A Vandana Sharma
%J ISRN Polymer Science
%D 2013
%R 10.1155/2013/590682
%X The dielectric relaxation behavior of thermotropic liquid crystal copolyester of 73% of p-hydroxy-benzoic acid (HBA) and 27% of 2-hydroxy-6-naphthoic acid (HNA) (Vectra-A) at poling temperature 80¡ãC has been studied using thermally stimulated depolarization current (TSDC) technique in the temperature range from 15¡ãC to 250¡ãC. The TSD currents were obtained for different polarizing fields ranging from 3.8£¿kV/cm to 19.2£¿kV/cm. TSD current spectra in the temperature range from 15¡ãC to 250¡ãC show three current maxima around 25¡ãC, 110¡ãC, and 220¡ãC. The maxima around 25¡ãC and 110¡ãC correspond to characteristic dipolar relaxations ¦Â and ¦Á, respectively. The peak around 220¡ãC is due to space charge effects named as ¦Ä-relaxation. The various relaxation parameters like activation energy (U), relaxation strength , preexponential factor , the quantity of charge released (Q) and concentration of trap for ¦Â- and ¦Á-relaxations at polarizing temperature 80¡ãC for different polarizing fields were evaluated using Bucci-Fieschi fit. The linear variation between activation energy and natural logarithm of preexponential factor indicates the presence of compensation effect for dipolar relaxations of Vectra-A under present poling conditions. 1. Introduction Liquid crystal copolymers of hydroxybenzoic and hydroxynaphthoic acids have received much interest due to their high chemical resistant which makes them suitable for making surgical instruments; their easily molded sheets have very good dimensional accuracy and strength and stiffness, and high strength-to-weight ratio makes them suitable for metal replacement applications. The dielectric and electrical properties of liquid crystal polymer (LCP) are strongly influenced by the molecular order and orientation. Thermally stimulated discharge current (TSDC) is a powerful tool for determining the characteristics of dielectric relaxation behavior of polymeric materials [1¨C4]. The advantage of this technique is its high sensitivity. In the present work, TSDC technique has been used to investigate the dielectric relaxation behavior of liquid crystal copolyester of 73% of p-hydroxybenzoic acid (HBA) and 27% of 2-hydroxy-6-napthoic acid (HNA) commercially known as Vectra-A in the temperature range from 15¡ãC to 250¡ãC at poling temperature 80¡ãC. The TSD currents were obtained as a function of temperature for polarizing fields ranging from 3.8£¿kV/cm to 19.2£¿kV/cm. The TSDC spectra were analyzed using Bucci-Fieschi-Guidi analysis [5]. The relaxation parameters activation energy, relaxation strength, preexponential factor, charge released,
%U http://www.hindawi.com/journals/isrn.polymer.science/2013/590682/