Surface Modification Of Inorganic Dielectric Fillers And Their Effect On The Electromechanical Properties Of Natural Rubber Composites

Dielectric elastomer（DE）is an intelligent material that can convert electrical energy into mechanical energy.With advantages of large deformation,fast response speed,and high electromechanical conversion efficiency,DE has been widely used in aviation,bionic muscles,and micro robots.When the external electric field was applied on DE,it could deform largely with the increase of voltage.When the external electric field was removed,the actuator could return to its original state.However,the deformation process of dielectric elastomer needs to be completed under high external voltage.Therefore,one of the challenges in this field is to prepare a kind of DE,which can obtain large deformation under low voltage.In this thesis,dielectric particles were modified by biomimetic method to improve the interfacial compatibility between dielectric particles and natural rubber（NR）matrix and electromechanical sensitivity dielectric elastomer composites,in order to prepare a kind of dielectric elastomer composites which can produce a large deformation under low electrical field.In the third chapter of this paper,firstly,the titanium dioxide（TiO₂）nanoparticles were deposited with the poly（catechol/polyamine）（PCPA）.Secondly,the PCPA-coated TiO₂ nanoparticles were further grafted withγ-methacryloxypropyl trimethoxy silane（KH570）to prepare TiO₂-PCPA-KH570 nanoparticles.Thirdly,different parts of TiO₂-PCPA-KH570 nanoparticles were added into NR matrix to prepare TiO₂-PCPA-KH570/NR composites.Because the C=C bond in KH570participated in the crosslinking reaction of NR,the dispersion of TiO₂filler in NR was improved,the polarization of filler/matrix interface was enhanced,and the dielectric and electromechanical properties of the composites were improved.Finally,the 10 phr TiO₂-PCPA-KH570/NR composite exhibited an electrical actuated strain of 12.3%at 70 k V/mm,which was about 2 times of the maximum electrical actuated strain of pure NR（6.0%）.In addition,the electrical breakdown strength of NR composites was improved by the PCPA-KH570 insulation layer effectively.In the fourth chapter of this paper,the modified TiO₂ nanoparticles,named m TiO₂,were prepared by grafting silane coupling agent KH570onto the surface of TiO₂ nanoparticles.Next,the natural rubber matrix was filled with different parts of m TiO₂ nanoparticles to prepare the m TiO₂/NR composites.It was found that the 10 phr m TiO₂/NR composite had the best mechanical and electrical properties.In order to further improve the electrical actuated strain of 10 phr m TiO₂/NR composite,dioctyl phthalate DOP plasticizer was added to it.The introduction of DOP could effectively reduce the interaction between NR molecular chains and weak the enhancement effect of filler network,which significantly reduced the elastic modulus of the composites.Under the electric field of 40 k V/mm,the maximum actuated strain of 50 phr DOP/m TiO₂/NR composite was 25.3%,which was 3.6 and 10 times of 10phr m TiO₂/NR composite（6.9%）and pure NR（2.6%）,respectively.In addition,the composite exhibited a stable electric actuated strain under repeated electrical field cycling.In the fifth chapter,boron nitride（BN）was modifed by bio-inspired dopamine modification,denoted as BN-PDA.Then the BN-PDA was dispersed into the natural rubber matrix to prepare dielectric elastomer composites,denoted as BN-PDA/NR.Because the PDA could effectively improve the dispersion of BN in NR matrix,the dielectric strength,energy density,mechanical properties and thermal conductivity of BN-PDA/NR composites were significantly improved.The 30 vol%BN-PDA/NR composite exhibited a high dielectric strength（126 k V/mm）and a high energy density（250 k J/g）.In addition,the thermal conductivity of the 30 vol%BN-PDA/NR composite was 0.46 W/m K,which was about 460%of pure NR（0.10 W/m K）.