Enhancement of dielectric properties with the addition of bromine and dopamine modified barium titanate particles to sil
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esearch Letter
Enhancement of dielectric properties with the addition of bromine and dopamine modified barium titanate particles to silicone rubber Liang Jiang, Centre for Elastomer Research, Focas Research Institute, Dublin Institute of Technology, Dublin 8, Ireland David Kennedy, Department of Mechanical Engineering, Dublin Institute of Technology, Dublin 1, Ireland Stephen Jerrams, Centre for Elastomer Research, Focas Research Institute, Dublin Institute of Technology, Dublin 8, Ireland Anthony Betts, Applied Electrochemistry Group, Focas Research Institute, Dublin Institute of Technology, Dublin 8, Ireland Address all correspondence to Liang Jiang at [email protected] (Received 20 July 2016; accepted 24 October 2016)
Abstract Dual-coated barium titanate (BT) particles were prepared using dopamine (DP) in conjunction with bromine (Br) in order to enhance the dielectric constant of silicone rubber (SR) composites containing evenly distributed BT particles. The results showed that both DP and Br were deposited on the BT particles. The dielectric constant of the SR/BT composite was significantly increased from 3.6 to 4.7 at 1 kHz with the addition of BT modified with dopamine (DP–BT). Moreover, the dielectric constant further rose to 4.9 at 1 kHz when the DP–BT particle was grafted with bromine (Br–DP–BT).
Introduction Dielectric elastomers (DEs) can respond to electrical stimuli by changing their shapes and belong to the family of smart materials.[1–3] Generally, DEs can induce several levels of strains (from 10% to 300%), but they require large electric fields (usually about 100 V/μm) to achieve large actuated strains.[4] It has been reported that the operating electric field of DEs could be decreased for these materials by increasing the DEs’ dielectric constants and also through lowering Young’s modulus.[5] A soft silicone rubber (SR)-based DE has the advantages of low Young’s modulus combined with lower viscoelasticity and good thermal stability.[6] However, its deformability under an electric field is limited with a low inherent dielectric constant (≈2.9).[2,6] The most popular approach to increasing the dielectric constant is by incorporating nano/micron-sized highdielectric filler particles into the DE matrix. Examples of fillers used are titanium dioxide (TiO2),[7–9] lead magnesium niobate– lead titanate (PMN–PT),[10,11] barium titanate (BT)[12,13] and functionalized graphene sheet.[14] Ferroelectric oxides, which exhibit a spontaneous electric polarization can also be reoriented in an external field. In particular, these oxides possess a large dielectric constant. Perovskite BT is one example of such oxides and exists as a white powder. It has a highdielectric constant of above 1200.[15] Nevertheless, inorganic BT has poor compatibility with SR and this disadvantage prevents its further application in soft actuators. To negate this limitation, researchers focused on surface modification of BT.[13,16] Dopamine, which can interact strongly with metal oxides by forming hydrogen bonds,[17] was considered an effecti
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