Rheological characterizations of ionic liquid-based gel polymer electrolytes and fumed silica-based composite polymer electrolytes S. Ramesh * , Chiam-Wen Liew Centre for Ionics University Malaya, Department of Physics, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia Received 8 November 2011; received in revised form 11 December 2011; accepted 19 December 2011 Available online 27 December 2011 Abstract In this work, two different polymeric systems were investigated. Ionic liquid-based gel polymer electrolytes (IL-GPEs) are designated as the first system and composite polymer electrolytes (CPEs) with addition of nano-sized fumed silica (SiO 2 ) are assigned as the second system. From amplitude sweep and oscillatory shear sweep tests, it was found out that the values of storage modulus (G 0 ) are much higher than loss modulus (G 00 ), indicating the elastic behavior of these samples. No behavioral transition of samples was observed in the tests. Linear visco-elastic range (LVE) of samples becomes wider with increasing content of ionic liquid and SiO 2 . Long-term structural stability was enhanced upon addition of ionic liquid. In the frequency sweep test, the absence of G 00 further confirmed the solid properties of samples. The inclusion of SiO 2 did not show any improvement in the frequency sweep test. The zero-shear viscosities were reduced upon inclusion of ionic liquid and SiO 2 . In the viscosity curve, the decrement of viscosity was shown as increase in shear rate due to the structural changes. # 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: Rheological behavior; BmImTFSI; SiO 2 1. Introduction In recent years, many researchers have shown keen interest in ionic liquid-based gel polymer electrolytes. In general, ionic liquids are composed of bulky organic cations and inorganic anions [1]. These room temperature molten salts have low melting point with some attractive characteristics. These inherent properties are wide electrochemical potential win- dow, relatively high ionic conductivity, non-volatility, non- flammability, negligible vapor pressure, excellent thermal and chemical stabilities as well as high ability to solubilize both organic and inorganic compounds [2–4]. However, the mechanical stability of ionic liquid-based polymer electrolytes may not reach the desirable level. Therefore, inorganic reinforcement filler is introduced to enhance the mechanical strength. This results the formation of composite polymer electrolytes (CPEs). In this work, fumed silica (SiO 2 ) is embedded into the polymer matrix to improve mechanical properties of polymer electrolytes. Fumed silica is a hydrophilic material prepared through vapor phase hydrolysis of silicon tetrachloride (SiCl 4 ) through thermal combustion in a hydrogen–oxygen flame atmosphere. Formation of three- dimensional network is originated by its native surface group on the fumed silica through hydrogen bonding and Van der Waals attractive forces. This native surface group is so-called as silanol (Si–OH) [5,6]. Upon addition of ionic liquid, the polymer electrolytes show the gel appearance. The viscosity of these gel polymeric systems would be decreased as ionic liquid manifests low viscosity. As aforementioned, fumed silica forms hydrogen bonds and Van der Waals of native Si–OH on the surface of fumed silica. However, these interactive bonds may be partially replaced by other functional group. An internal network structure which may result from physical bonds (known as physical gel) is formed through hydrogen bonding and/or Van der Waals attraction of native or functional surface groups when fumed silica is incorporated in the polymer matrix. This type of gel is able to flow under shear by disrupting the physical bonds between the fumed silica and polymer matrix. However, the physical bonds reform when the shear is removed [5]. Therefore, the physical properties of polymer electrolytes are the main features in this work. www.elsevier.com/locate/ceramint Available online at www.sciencedirect.com Ceramics International 38 (2012) 3411–3417 * Corresponding author. Tel.: +60 3 7967 4391; fax: +60 3 7967 4146. E-mail address: rameshtsubra@gmail.com (S. Ramesh). 0272-8842/$36.00 # 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2011.12.053