Indian Journal of Pure & Applied Physics Vol. 45, November 2007, pp. 910-919 Electrical conduction behaviour of pristine and 100 MeV Ni ion irradiated PET/0.8PHB polymer liquid crystals J K Quamara*, Y Sridharbabu**, Geetika Goyal & Anu Sharma Department of Applied Physics, National Institute of Technology, Kurukshetra 136 119 Received 19 February 2007; accepted 18 Sepember 2007 Electrical conduction behaviour of pristine and 100 MeV Ni ion irradiated terephthalate (PET)/0.8 poly(p-hydroxy- benzoic acid) (PHB) polymer liquid crystals has been investigated in transient and steady state conditions at different electric fields (13-104.3 kV/cm) and temperatures (40-250°C). The various mechanisms responsible for charge transport phenomena can be thoroughly investigated by studying temperature and field dependent conduction behaviour. The origin of transient currents in polymers has been ascribed to number of mechanisms. The dipolar relaxation seems to be the major contributor to these currents at lower temperatures. The temporal decay of current may be due to trapping of charge carriers and/or due to the reduction of electric field owing to the formation of Schottky layers in the vicinity of the electrodes. The high temperature relaxations do not contribute much to the transient behaviour. The transient currents in ion irradiated samples are mainly governed by cross-link structures and free radical formation in addition to the δ-transition. Poole- Frenkel and Schottky conduction mechanisms appear to operate at high and low temperature regions, respectively, for both pristine and irradiated samples. Keyword: Liquid crystals, Electrical conduction, Pristine, Polymer IPC Code: C30B 1 Introduction Polymer liquid crystals (PLCs) have attracted the attention of numerous scientists and technologists because of their promising mechanical, electrical and non-linear optical properties 1-9 . Despite their fascination for many applications the conduction mechanism in polymer liquid crystals is not well understood till date. Though the electrical conduction in polymers is relatively poor owing to very few free electrons available, the I-V characteristics can provide a very good understanding between microscopic molecular structure and macroscopic electrical properties of polymers 10-12 . The various mechanisms responsible for charge transport phenomena like Poole Frankel, hopping, Schottky emission and tunneling can be thoroughly investigated by studying temperature and field dependent conduction behaviour 13 . The present paper principally concerns with the study of electrical conduction behaviour of pristine and high energy Ni ion irradiated PET/0.8PHB polymer liquid crystals. 2 Experimental Details The polymer liquid crystal used in the present investigations is a copolymer of polyethylene terephthalate [PET] and poly(p-hydroxybenzoic acid) [PHB], henceforth, referred to PET/0.8.PHB, 0.8 represents the mole fraction of crystalline PHB sequences in the copolymer. The chemical structure of the PET/0.8.PHB is shown below. n The samples procured from Eastman Kodak (USA) were of 150 µm nominal thickness. The samples were irradiated with 100 MeV Ni ion (fluence: 9.77×10 11 ions/cm 2 ) using PELLETRON facility at Nuclear Science center, New Delhi, India .The experimental set up used for electrical conduction measurements is shown in Fig. 1. The conduction measurements at ______________ *E-mail: jkquamara@yahoo.com **Present Address: Lingaya’s Institute of Technology and Management, Nachauli, Faridabad 120 002 Fig. 1 — Schematic diagram of Electrical Conduction experiment