Mechanically Compliant Electrodes and Dielectric Elastomers from PEG-PDMS Copolymers
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Mechanically Compliant Electrodes and Dielectric Elastomers from PEG-PDMS Copolymers Aliff Hisyam A Razak1,2, Frederikke Bahrt Madsen1 and Anne Ladegaard Skov1 1 Danish Polymer Center, Department of Chemical and Biochemical Engineering, Technical University of Denmark, Building 227, 2800 Kgs. Lyngby, Denmark. 2 Faculty of Engineering Technology, University of Tun Hussein Onn Malaysia, 86400 Parit Raja, Batu Pahat, Johor, Malaysia. ABSTRACT Soft conducting elastomers have been prepared from polydimethylsiloxanepolyethyleneglycol (PDMS-PEG) copolymer and surfactant-stabilized multi-walled carbon nanotubes (MWCNTs). The copolymer was chain-extended with PDMS of molecular weight 17.2 kg mol-1 in order to obtain a crosslinkable PDMS with molecular weight around 20 – 30 kg mol-1. MWCNTs were treated with surfactant and sonicated for better dispersion in the polymer matrix. The conductivity and mechanical properties of conducting elastomers were thoroughly investigated including stress and strain at break. The developed conducting elastomers showed high conductivity combined with inherent softness. The high conductivity and softness, PDMSPEG copolymers with incorporated MWCNTs hold great promises as compliant and highly stretchable electrodes for stretchable devices such as electro-mechanical transducers. INTRODUCTION Stretchable, conductive materials have been extensively studied for many applications such as biomedical devices [1], electro-mechanical transduction [2] and solar power [3]. For the dielectric elastomer (DE) technology, an inherently soft and highly conductive compliant electrode material is required for optimum performance in electro-mechanical transduction. Conventional compliant electrodes, such as carbon black in the form of powder and carbon grease, can be easily applied on surfaces, but they lack adhesion to the elastomer. Other investigated electrode materials for DEs include silver nanowires, ionic hydrogels, single-walled carbon nanotubes (SWCNTs) and polymer-carbon conductive composites [2]. These materials however suffer from poor stretchability which renders them unattractive as flexible electrodes [2]. On the other hand, commercial conductive elastomers such as LR3162 from Wacker Chemie have high conductivity, but they contribute with a stiffening effect due to their high Young’s modulus. As an alternative to the above mentioned materials polydimethylsiloxanepolyethyleneglycol (PDMS-PEG) copolymers, which are somewhat conductive with conductivities around 10-8 S cm-1 [4], have great adhesion to silicone surfaces and great flexibility and compliance due to their partly silicone nature. Furthermore, their moderate conductivities can be easily enhanced by incorporating highly conductive nano-fillers such as multi-walled carbon nanotubes (MWCNTs). The high interaction energies of MWCNTs due to strong van der Waals forces, however, often result in poor dispersibility and weak interfacial interactions with the matrix[5]. Well-dispersed MWCNTs are important in order to avoid agglomeration which would g
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