| Dielectric elastomer(DE)is a kind of electroactive polymer,which has three applications including dielectric elastomer actuator(DEA),dielectric elastomer generator(DEG)and dielectric elastomer sensor(DES).In recent years,DEA and DES have attracted great interest of researchers.For DEA,it typically composes of a thin dielectric elastomer(DE)film sandwiched between two compliant electrodes on both sides,and it is considered as the research direction of the new generation of artificial muscle.The shape of DE film can be changed by applying voltage on the electrode,in which electrical energy can be converted into mechanical energy.For DES,it is a device that can convert mechanical signal to electrical signal by taking advantage of the capacitance difference between initial state and stretching state,and its essence is a capacitive strain sensor.At present,silicone rubber(SiR)with low modulus and human compatibility is often used as DE material,but its low dielectric constant(ε’)limits the application of DEA and DES.Therefore,the key to the development of new generation of DEA and DES is to design and prepare new type of SiR DE materials with high ε’,and thus the large actuated strain at low electric field and high capacitance different at low strain were obtained.According to the previous work,too many strategies were employed to improve the ε’of SiR by improve the dipole polarization ability or interface polarization ability individually.The dipole polarization ability of DE can be enhanced by the synthesis of DE with new structure or chemical modification with polar dipole groups for polymer chain.By adding ceramic fillers with highε’or conductive fillers,a large difference in dielectric or conductive properties between the fillers and the matrix can be formed,which can enhance the interfacial polarization ability of DE.However,in order to effectively improve the ε’of DE,a large amount of fillers need be added,which will inevitably deteriorate the mechanical properties of DE.It is found that the enhancement of the dipole polarization ability of DE can promote the interfacial polarization ability and a synergistic effect can be obtain on the increase of the ε’.Therefore,the addition of a small amount of filler into the polar matrix can greatly enhanceε’,which provides guidance and inspiration for the design and application of high-performance DE.In this work,based on the synergistic effect of dipole polarization and interfacial polarization,the "polar group&ceramic filler" system and "polar group&conductive filler" system were designed to prepare high-performance SiR DE composites.The innovative work and results are as follows:(1)Preparation and actuation performance of E-TiO2/PMVS-COOH dielectric elastomer compositesBy introducing polar functional groups and multi-functional ceramic fillers,we designed and prepared the SiR DE composite as micro-actuator,and enhanced its tensile strength,dielectric constant and actuated strain at low electric field.Firstly,carboxyl groups were grafted onto PMVS chains by using the thiol-ene click reaction,leading to the improvement of dipole polarizability.Then,E-TiO2 particles were prepared and filled into PMVS-COOH,and the crosslinking reaction between carboxyl groups from PMVS-COOH and epoxy groups from E-TiO2 occurred.Thus,E-TiO2 plays multiple-functional roles including:acting as crosslinking agent for the crosslinking of PMVS-COOH,acting as good reinforcing filler to enhance tensile strength,providing good interfacial polarizability.As a result,the tensile strength largely increases from 0.33 MPa to 0.89 MPa as the content of E-TiO2 increases from 10 phr to 30 phr.The dielectric constant at 103 Hz of the composite with 30 phr E-TiO2 reaches 8.98,which is 3.3 times as reference SiR due to the simultaneously improved dipole and interfacial polarizability.The actuated strain at low electrical field(15 kV·mm-1)of the composite with 30 phr E-TiO2 reaches 3.7%without any pre-strains,which is 5.2 times than that of reference SiR.(2)Preparation and sensing performance of CNT-PDA/multiblock copolymer dielectric elastomer compositesThrough molecular design and introduction of conductive filler,high dielectric constant and high capacitance SiR DE composite for capacitive strain sensor were designed and prepared.Firstly,a polar(bis(3-aminopropyl)terminated poly(3,3,3-trifluoropropyl)methylsiloxane(H2N-PFMS-NH2))and a nonpolar(bis(3-aminopropyl)-terminated poly(dimethylsiloxane)(H2NPDMS-NH2))silicone oligomers were synthesized by anionic ring opening polymerization.Then,a series of PFMS/PDMS multiblock copolymer were synthesized through a one-pot polycondensation reaction between isocyanate groups from methylene-bis(4-cyclohexylisocyanate)and amino groups from the as prepared H2N-PFMS-NH2 and H2N-PDMS-NH2.And then,the CNT-PDA was prepared and introduced into the multiblock copolymers,which can further improve the dielectric and sensing properties of the polymer.The CNTPDA/multiblock copolymer composite with only 0.3 vol.%of CNT-PDA exhibits a dielectric constant of about 86.7 at 103 Hz and ΔC of about 0.91 nF at 200%strain,which was increased by 23.8 and 8.1 times,respectively,compared with that of CNT-PDA/reference SiR composite. |
