Synthesis And Properties Of Dielectric Elastomers With Low Modulus And High Dielectric Constant

Dielectric elastomers, as a new class of electric actuated material, have attracted interest of a large number of researchers since they were discovered in the early 1990s. Compared with other actuator materials, dielectric elastomers have some unique advantages in properties, such as great actuated strain, high actuated energy density, quick strain response, low dielectric loss and good tolerance to temperature and humidity. These excellent performance also provide dielectric elastomers wide application field and huge application potential. At the same time, the development of dielectric elastomers face some challenges. The key factors of improving the performance of dielectric elastomers are dielectric constant and Young’s Modulus. This project aims at synthesizing a kind of dielectric elastomer with high dielectric constant and low Young’s Modulus. The main work and results are as follows:1. A series of polyurethane elastomers with different ratio of NCO/OH and different chain-extenders were synthesized using HDI and PTMG. The structure of PU was characterized by FTIR. Also, the thermal, mechanical, dielectric and electric actuated strain properties of PU were investigated. Some results were discovered as follows:with the increase of ratio of NCO/OH, the glass transition temperature increased and Young’s Modulus first increased and then decreased, but generally all the modulus were too high and the lowest modulus was 6.73MPa. The dielectric constant of PU almost stayed the same when the ratio of NCO/OH changed, and the dielectric constant reached to about 8 which was 33% higher than other PU elastomers(ε=3-6) at least. About to the PU elastomers with different chain-extenders, PU elastomers with longer chain of chain-extender had a lower glass transition temperature and dielectric constant which decreased from 7.35 to 3.03. Although the modulus decreased at the same time, the dielectric constant decreased more rapidly. It resulted in a lower ratio of dielectric constant and Young’s Modulus, which was harmful to actuated strain. Generally speaking, compared with other PU elastomers, PU elastomer with relatively high dielectric constant was synthesized while the modulus was still a problem which need more exploration.2. A series of polyester elastomers called PEC were synthesized using PEG and CA as monomers, and their properties were explored. The results indicated that PEC had a very high dielectric constant (reached to about 21) which was almost higher than any other dielectric elastomer matrix materials. And with the decrease of CA content in PEC, the dielectric constant of polymer decreased slightly. While the modulus decreased also, and it decreased from 1.42MPa (PEG/CA=3:2) to 0.7MPa (PEG/CA=1:1); thus PEC showed better electric actuated properties when the ratio of PEG and CA was 1:1. An actuated strain of 8.27% was obtained under the field of 14.7kV/mm. So the project purpose was achieved by synthesis of PEC polyester elastomers with a low modulus and high dielectric constant. Furthermore, it is foreseeable that PEC will be of great potential as a dielectric elastomer matrix.