Design, Preparation, And Properties Of Novel Dielectric Elastomer Composites

Dielectric elastomers (DEs) are one kind of smart materials, are capable of converting electrical energy to mechanical energy. Getting a large actuated strain at a low driving electric field is a big challenge for dielectric elastomer research field. Novel dielectric elastomer expect to have low elastic modulus and high dielectric constant, exhibit high actuated strain on low electric field, and maintain the stability of actuated strain. In this paper, based on obtaining an excellent dielectric elastomer with large actuated strain on low electric field, a series of dielectric elastomer materials were designed and prepared.In the third chapter, a high performance dielectric elastomer was prepared through adding a high-dielectric-constant ceramic filler lead magnesium niobate (PMN) into silicone elastomer (PDMS), and adjusted the elastic modulus through changing the crosslink density or adding plasticizing agent into composites. At last, we got a high performance dielectric elastomer composite and confirmed that the actuated strain of DE was determined by both the dielectric constant and the elastic modulus. Although the dielectric constant of silicone elastomer increased with increasing loading amount of ceramic particles, the actuated strain didn’t increase obviously as expected because the elastic modulus increased at the same time. Reducing the crosslink density or adding plasticizing agent into composite can obviously decrease the elastic modulus of silicone elastomer, leading to a visible increase in actuated strain.Hydrogenated nitrile-butadiene rubber (HNBR), which contains a large amount of strong polar groups, exhibits a high dielectric constant. In fourth chapter, a series of dielectric elastomer based on HNBR material was prepared. First, tuning the crosslink density of the elastomer and adding the plasticizer dioctyl phthalate (DOP) into the HNBR elastomer, an excellent dielectric elastomer was obtained. Second, titanium dioxide (TiO2) as the high-dielectric-constant filler and a nontoxic epoxidized soybean oil (ESO) as the plasticizer were introduced into a hydrogenated nitrile-butadiene rubber matrix to form a dielectric elastomer. This dielectric elastomer with excellent properties was obtained by simultaneously controlling the filler network and molecular interaction in the polymer matrix through changing amount of TiO2and ESO. At last, bio-inspired dopamine was used to functionalize the surface of barium titanate particles (BaTiO3) to improve interfacial interaction between the BaTiO3particles and HNBR matrix containing ESO. This method effectively improved the filler dispersion, leading to obviously increased dielectric properties and actuated strain of composites.In fifth chapter, a new polyester dielectric elastomer was synthesized. This polyester has not only high dielectric constant but also low glass transition temperature. In addition, the polyester elastomer can exhabit a large actuated strain at low electric field. In order to further improve the electromechanical performance of the polyester elastomer, high-dielectric-constant TiO2particles was added into polyester elastomer matrix. The results showed that the TiO2particles can decrease the crosslink density of composites. At a suitable content of TiO2particles, a lower elastic modulus of polyester composite than that of pure polyester elastomer was obtained, leading to a larger deformation of the polyester elastomer composite than that of pure polyester elastomer.In sixth chapter, slide-ring (SR) was selected as a dielectric elastomer material. The slide-ring (SR) materials with a necklace-like molecular structure in which many cyclic molecules (a-cyclodextrin (a-CD)) grafted with poly-ε-caprolactone (PCL) as the mobile side chains are threaded onto a linear poly(ethylene glycol)(PEG) molecule with two bulky end groups. These polyrotaxane (PR) chains are crosslinked by coupling the a-CD ring with crosslinking the terminals of the PCL side chains. The figure-of-eight crosslinks, which comprise two cyclic molecules, can slide along the polymer chains and thereby behave as pulleys to equalize the internal stresses in the SR materials. The special properties of SR material lead to the SR material exhibited a high actuated strain on a low electric field. In order to further improve the electromechanical performance of the SR materials, y-methacryloxypropyl trimethoxy silane (KH570) modified BaTiO3particles was introduced into SR matrix to improve the actuated performance. The actuated strain was obtained by SR composite was much more excellent than most of other dielectric elastomers reported in the literature.A dramatically increase of dielectric constant can be achieved by adding conductive particles into the polymer matrix until the percolation threshold. Nevertheless, the conductivity and dielectric loss dramatically increase as a result limit the application of dielectric materials. In order to overcome the disadvantage, the seven chapter firstly synthesized a novel multilayer core/shell conductive micro-particles by biomimetic poly(dopamine) coating, with silica/poly(dopamine)/silver core and poly(dopamine) shell (denoted as SiO2/PDA/Ag/PDA). The dielectric and electrical properties of composite can be easily controlled by adjusting the outer poly(dopamine) shell thickness, leading to the composite has a high dielectric constant, a low dielectric loss, and a low conductivity.