Multiple Relaxations in Poly (p-hydroxybenzoic acid-CO-ethylene terephthalate) Liquid Crystal Polymer: TSD Current Inves
- PDF / 295,503 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 59 Downloads / 142 Views
0949-C03-20
Multiple Relaxations in Poly (p-Hydroxybenzoic Acid-CO-Ethylene Terephthalate) Liquid Crystal Polymer: TSD Current Investigations Jitendra Kumar Quamara, Sridharbabu Yarramaneni, and Geetika Goyal Department of Applied Physics, National Institute of Technology, Kurukshetra, India ABSTRACT
The PET/x.PHB samples were polarized at different temperatures (30-2500C) under various biasing fields ranging from 40 to 200 kV/ cm. The TSD currents were obtained at a heating rate of 2 0C/min in the temperature range (15-250)0C. The TSD current spectra in general comprise of three maxima namely β, α and δ in ascending order of temperature. However number of peaks actually appearing in these spectra, their location, height and sharpness are governed by polarization/depolarization parameters as well as the value of ‘x’ in a particular sample. The β peak appearing around (110-1400C) has been recognized as a dipolar relaxation process and is due to PET rich phase. The α- peak (160-1800C) recognized as space charge process is due to PHB rich phase and cold crystallization of PET rich phase. The δ peak (190-2100C) is a melting process due to the movement of large segments leading to Smectic-E like phase. In addition PET/x.PHB also exhibit a weak low temperature dipolar relaxation process β′ peak around (30-40)0C. In the vicinity of α-relaxation a rigid amorphous phase dipolar relaxation process γ relaxation is also observed. INTRODUCTION The liquid crystalline state in the polymers was reported in the year 1937 by Bawden and Pirie [1]. It was observed that under certain conditions of temperature, pressure and concentration some of the polymers (termed as polymer liquid crystals, PLC) exhibit this liquid crystalline behavior. Considerable amount of work has been reported on polymer liquid crystals [2-3]. The major work reported is related to thermal properties, visco elastic behavior, processability and mechanical properties. The present paper is principally concerned to elaborate in detail the TSD current behavior in pristine PET/x.PHB PLC samples (x = .8) under various polarizing and depolarizing conditions. MATERIAL AND METHODS The polymer liquid crystal used in the present investigations is a copolymer of polyethylene terephthalate [PET] and poly(p-hydroxybenzoic acid) [PHB]. This will be referred to as PET/0.8 PHB where 0.8 represents the mole fraction of the liquid crystalline PHB sequences in the copolymer. C
C
O
C H2
2
O
C
O
x y O O O Fig1: Structural unit of poly(p-hydroxybenzoic acid-co-ethylene terephthalate) polymer liquid crystal.
The samples were procured from Eastman Kodak (USA). The electrical contacts were made by vaccum evaporation of aluminum onto both surfaces. The samples were polarized by following the usual method [5]. The samples were then cooled to the room temperature within fixed time(1/2 h) in the presence of Ep. The frictional stray surface charges accumulated during polarization were eliminated by short-circuiting the electrodes for about 10 min. In order to obtain depolarization cu
Data Loading...
