Preparation Of High-performance Dielectric Composites By Biomimetic Method Toward Dielectric Filler

Dielectric elastomers（DEs）are electronic polymers,which are one kind of electroactive polymers（EAPs）.With an external electric field is applied,the EAP can significantly change its shape and size.When the applied external electric field is cancelled,it can return to its original shape and size;in addition,when the EAP is deformed,a corresponding electrical signal can be generated.DEs have the advantages of large deformation,fast response speed,and high electromechanical conversion efficiency,which can be applied to various applicatons,such as bionic muscles,aviation,small generators,and capacitors.However,the high driving voltage required by the dielectric elastomer and the generally low dielectric constant of dielectric elastomer limit its wide application.In this paper,the dielectric filler was firstly modified via bimmimetic method and then added into the nitrile-butadiene rubber（NBR）matrix to prepare high performance dielectric elastomers.In Chapter 3 of this paper,TiO₂ nanoparticles are first modified by non-covalent deposition of poly（catechol/polyamine）（PCPA）,and then grafted withγ-（2,3-glycidoxy）-propyl trimethoxysilane（GPTMS）to form TiO₂-PCPA-GPTMS nanoparticles.The modified TiO₂-PCPA-GPTMS nanoparticles enhanced the mechanical,dielectric and electromechanical properties of NBR composites.The NBR composite filled with 10 phr of TiO₂-PCPA-GPTMS showed an actuated strain of about 11%under an electric field of 47 k V/mm,which was about 230%of pure NBR（4.8%）.In Chapter 4 of this paper,the boron nitride（BN）was firstly modified by dopamine for introducing catechol and amino groups,then followed by grafting withγ-（2,3-epoxypropoxy）propytrimethoxysilane（KH560）to form BN-PDA-KH560 platelets.The as-prepared BN-PDA-KH560platelets were added into NBR matrix to prepare composites with high thermal conductivity and dielectric constant.The results showed that the30 volume（vol）%BN-PDA-KH560/NBR composite achieved a large thermal conductivity（0.409 W/m K）,which was 2.6 times higher than pure NBR（0.157 W/m K）.In addition,the 30 vol%BN-PDA-KH560/NBR composite not only exhibited a relatively high dielectric constant（9 at 100Hz）,but also maintained a low dielectric loss angle（0.12 at 100 Hz）.In Chapter 5 of this paper,the high-dieletric-constant BaTiO₃ was first modified with dopamine for introducing poly（dopamine）（PDA）functional layer.Then the[Ag（NH₃）²]⁺ions were adsorbed by the catechol and amine groups on PDA and reduced into the silver nanoparticles via electroless plating to synthesis of core-satellite structured（BT-PDA-Ag）nanoparticles.The prepared BT-PDA-Agnanoparticles were added into NBR matrix for improving the dielectric properties.Due to the increased conductivity of the filler/matrix interlayer and Ag nanocapacitor structure in NBR composites,the dielectric constant of NBR nanocomposites increased.In addition,the ultrasmall Ag nanoparticles trapped the carriers by Coulomb blockade and quantum confinement effects,which resulted in low dielectric loss and low electrical conductivity of nanocomposites.