Intrinsically Tuning the Electromechanical Properties of Elastomeric Dielectrics: A Chemistry Perspective

Dielectric elastomers have the capability to be used as transducers for actuation and energy harvesting applications due to their excellent combination of large strain capability (100-400%), rapid response (10^-3  s), high energy density (10-150 kJ m^-3 ), low noise, and lightweight nature. However, the dielectric properties of non-polar elastomers such as dielectric permittivity ε_r , breakdown strength E_b , and dielectric loss ε ″, need to be enhanced for real world applications. The introduction of polar groups or structures into dielectric elastomers through covalently bonding is an attractive approach to 'intrinsically' induce a permanent polarity to the elastomers, and can eliminate the poor post-processing issues and breakdown strength of extrinsically modified materials, which have often been prepared by incorporation of fillers. This review discusses the chemical methods for modification of dielectric elastomers, such as hydrosilylation, thiol-ene click chemistry, azide click chemistry, and atom transfer radical polymerization. The effects of the type and concentration of polar groups on the dielectric and mechanical properties of the elastomers and their performance in actuation and harvesting systems are discussed. State-of-the-art developments and perspectives of modified dielectric elastomers for deformable energy generators and transducers are provided.