Conductivity and optical studies of plasticized solid polymer electrolytes doped with carbon nanotube Suriani Ibrahim n , Roslina Ahmad, Mohd Rafie Johan Advanced Materials Research Laboratory, Department of Mechanical Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia article info Article history: Received 3 May 2011 Received in revised form 29 July 2011 Accepted 5 August 2011 Available online 18 August 2011 Keywords: Polymer electrolyte Optical absorption spectra Band gap Band edge Carbon nanotube abstract Solid polymer electrolyte films based on Poly(ethylene oxide) (PEO) complexed with lithium hexafluorophosphate (LiPF 6 ), ethylene carbonate (EC) and amorphous carbon nanotube (aCNTs) were prepared by the solution cast technique. The conductivity increases from 10 10 to 10 5 Scm 1 upon the addition of salt. The incorporation of EC and aCNTs to the salted polymer enhances the conductivity significantly to 10 4 and 10 3 Scm 1 . The complexation of doping materials with polymer were confirmed by X-ray diffraction and infrared studies. Optical properties like direct band gap and indirect band gap were investigated for pure and doped polymer films in the wavelength range 200–400 nm. It was found that the energy gaps and band edge values shifted to lower energies on doping. & 2011 Elsevier B.V. All rights reserved. 1. Introduction In recent years, studies on the optical properties of polymers have attracted much attention in view of their application in optical devices [1–3]. The optical properties have been studied aimed at achieving better reflection, antireflection, interference and polarization properties [1]. The optical properties of polymers can be suitably modified by the addition of dopants depending on their reactivity with the host matrix [1]. A change in polymer composition may affect the induced optical absorption due to several reasons, namely the polarization power of network for- mers, modifiers, their coordination numbers, the concentration of non-bridging oxygen (oxygen ions having dangling bonds), the presence of multivalent network forming and modifying ions [4]. Studying the optical absorption, particularly the shape and shift of the absorption edge, is a very useful technique for understanding the basic mechanism of optically induced transitions in crystal- line and non-crystalline materials, as well as providing informa- tion about the energy band structure. Although some work has been done on the optical properties of doped polymer electrolyte films [5–15], no report is available on polymer electrolytes doped with carbon nanotubes. The investigation of the optical properties of this system is still limited and much experimental work needs to be done in this direction. Poly(ethylene oxide) is an exceptional polymer; it dissolves in high concentration of a wide variety of salts to form polymer electrolytes. Studies have proved that in PEO–LiPF 6 and PEO–LiCF 3 SO 3 systems, conductivity increases with the increase of salt wt%. [16–19]. This paper is concerned with the optical properties of new polymer electrolytes based on a Poly(ethylene oxide) complexed with lithium hexafluoropho- sphate (LiPF 6 ), ethylene carbonate (EC) and carbon nanotube. The neural network model has been developed and it was successful to predict the ionic conductivity of nanocomposites polymer electrolyte system [20,21]. The optical properties of the polymer electrolytes are investigated to determine the optical transition characteristics and provide information about the band structure and energy gap. 2. Experimental Polymer electrolytes were prepared by standard solution-casting techniques. PEO (MW¼ 600,000, Acros Organics) was used as host polymer matrix, lithium hexaflurosphosphate (LiPF 6 ) (Aldrich) as the salt for complexation and ethylene carbonate (EC) (Alfa Aesar) as plasticizer. Amorphous carbon nanotube (aCNT) was prepared by the chemical route at low temperature [22]. Prior to use, PEO was dried at 50 1C for 48 h. Appropriate quantities of PEO, LiPF 6 , EC and aCNT were dissolved separately in acetonitrile (Fisher) and stirred well for 24 h at room temperature to form a homogeneous solution. All samples were stored under dry conditions. An electronic digital caliper was used for measuring films thickness and average thickness for films is 0.76 mm. The ionic conductivities of the samples were measured at temperature ranging from 298 to 373 K Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence 0022-2313/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jlumin.2011.08.004 n Corresponding author. Tel.: þ60 123010248; fax: þ60 379675317. E-mail address: sue_83@um.edu.my (S. Ibrahim). Journal of Luminescence 132 (2012) 147–152