Transient and steady state currents of γ-irradiated 70/30 (wt/wt.%) polyvinyl alcohol/glycogen blend samples undoped and doped with eosin F.H. Abd El-kader b , S.A. Gaafer a , K.H. Mahmoud b, ⁎, S.I. Mohamed a , M.F.H. Abd El-kader a a Department of Biophysics, Faculty of Science, Cairo University, Giza, Egypt b Department of Physics, Faculty of Science, Cairo University, Giza, Egypt abstract article info Article history: Received 17 November 2007 Received in revised form 9 July 2008 Accepted 14 July 2008 Keywords: Charge transport dc conductivity Activation energy PVA/glycogen films Mobility The transient currents, I–V characteristics and dc electrical conductivity of 70/30 (wt/wt.%) polyvinyl alcohol (PVA)/glycogen undoped and doped with eosin films have been studied under different conditions before and after irradiation by γ-doses in the range 5–100 kGy. The conduction mechanisms operative in the films at different temperature and γ-irradiation ranges are estimated from the behaviour of Log I versus V 1/2 plots. The results show that both temperature and γ-irradiation affects the type of electronic transport mechanism for undoped blend sample. On doping with eosin, there is only considerable influence on the type of conduction with varying temperature but γ-doses have no significant effect. The dc conductivity for blend sample doped with eosin is found to increase by 1–2 orders of magnitude compared to the undoped sample at both different temperatures and γ-doses. The values of mobility and charge carrier concentration for all samples under investigation were found to vary from (0.26–2.22) × 10 - 4 m 2 V - 1 s - 1 and (0.52–76.20) × 10 24 m - 3 respectively. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Blending biopolymer glycogen with another flexible synthetic polymer such as PVA seems to be an attractive way for improving properties of the films. PVA and glycogen are nontoxic, water-soluble, that are widely used in biomedical applications [1–3]. PVA and glycogen chains are intimately mixed. Thermal and IR analysis [4,5] suggests that intermolecular interactions, consisting mostly of polar interactions owing to closely matched polarity, are likely present in the PVA/glycogen blend system. Organic dye-polymer composites have received considerable attention as potential electro- optic materials [6,7]. Whenever a polymer matrix is impregnated by dye (an impurity), it increases the charge stability and electric con- ductivity of the polymer, because charge transfer complexes (CTCs) are formed. Gamma irradiation of polymers has become one of the most com- mon processes producing modifications in their physical, chemical and morphological structure [8–10]. These modifications depend on the chemical nature of the polymer, radiation dose, dose rate and irradiation environmental conditions. The present work is carried out to investigate the effect of both addition of eosin and γ-irradiation on mobility, carrier concentration and the conduction mechanism in polymeric blend of 70/30 (wt/wt.%) PVA/glycogen. 2. Experimental PVA was supplied by BDH company, England. Its molecular weight is approximately 20,000 g/mol. The degree of hydrolysis is 87–89%. Glycogen was extracted from bovine liver supplied from Fluka Bio- chemica, USA.Its molecular weight approximately 50,000 g/mol. Eosin was supplied by Sterm chemicals company, USA with purity 99.9%. Its molecular weight 691.86 g/mol. A known amount of PVA granules was dissolved in a mixture of distilled water and ethanol with ratio 4:1 to prepare 2 wt.% solution at room temperature. Also, a known amount of glycogen was dissolved in distilled water to prepare 2 wt.% solution at room temperature. Solu- tions of PVA and glycogen were mixed together by weight percentage 70/30 (wt/wt.%) PVA/glycogen (system A), using a magnetic stirrer at 50 °C. Thin films of appropriate thickness (≈ 0.01 mm) were cast onto stainless steel Petri dishes and then dried in air at room temperature for about 6 days until the solvent was completely evaporated. Eosin of concentration 0.1 wt.% was added to the mixed solution of 70/30 (wt/wt.%) PVA/glycogen (system B) and the same procedure was carried out to form the film. The samples were irradiated by different γ-doses in the range 5–100 kGy using 60 Co source with a dose rate of 8.6 Gy/h at room temperature. For ohmic contacts, the surfaces of the sample were coated with silver paste. The sample was sandwiched between two copper elec- trodes. Current measurements were made by means of an electrometer (Keithley 617 Aurora Cleveland, Ohio, USA) which was carefully groun- ded to avoid extraneous electrical noise. Current–voltage characteris- tics were studied with an effective area ≈ 1 cm 2 in the temperature range 30–160 °C and voltage range 10–600 V. The electrical conductivity was Solid State Ionics 179 (2008) 2124–2131 ⁎ Corresponding author. E-mail address: cairouni1@yahoo.com (K.H. Mahmoud). 0167-2738/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.ssi.2008.07.012 Contents lists available at ScienceDirect Solid State Ionics journal homepage: www.elsevier.com/locate/ssi