聚硅氧烷分子刷共价包覆MWCNTs及其与硅橡胶复合物电致应变调控机理

Dielectric elastomers (DEs) are smart polymeric materials sandwiched between two compliant electrodes and are capable of displaying strains in response to an applied voltage. To overcome the present problems of strong interfacial polarization effect, high dielectric loss and low dielectric breakdown strength for DEs，multi-walled carbon nanotubes(MWCNTs) were first covalently encapsulated with polysiloxane brushes via the nitrene addition reaction between MWCNTs and mono-azide terminated polysiloxane (PDMSN3).Then the encapsulated MWCNTs were blended with silicone rubber to obtain the DE composites. Effects of MWCNTs contents, encapsulation ratios as well as chain length of the PDMS on the morphological, mechanical, dielectric and electromechanical straining properties of the composites were investigated. Filler-matrix compatibility, homogeneity as well as interfacial polarization effect were greatly improved due to the similar chemical compositions between the PDMS brushes and the silicone matrix. In addition, the relatively short PDMS chains can act as plasticizers and alleviate the hardening effect of MWCNTs. Therefore, high dielectric constant, low dielectric loss, high dielectric breakdown strength as well as low modulus DEs can be prepared and the unification of large electromechanical strain and high electromechanical stability can be realized for the present DE materials. This research can help to establish the theoretical foundation of encapsulating inorganic conductive fillers with polymer brushes in a controlled manner and provide new approaches for large-scale production of DEs with large electromechanical strains.

介电弹性体（DEs）为表面涂覆柔性电极并在电压下能够产生应变的智能高分子材料；为克服目前DE材料界面极化效应显著、介电损耗高、击穿场强低的弊端，本项目拟通过多壁碳纳米管（MWCNTs）与单叠氮端聚硅氧烷（PDMSN3）的双键叠氮环加成反应，生成表面可控共价包覆PDMS刷的MWCNTs，并将其与硅橡胶复合制备DE材料。研究MWCNTs含量、包覆率及PDMS链长对复合材料相形态、力学、介电及电致应变性能的影响。由于PDMS刷与基体同质，MWCNTs基体相容性提高、相态均一性加强，界面极化效应减弱；此外，短链PDMS刷可以增塑基体，缓解MWCNTs填充引起的硬化效应。因此，本DE材料具备介电常数高、介电损耗低、击穿场强高及弹性模量低的特性，从根本上实现高电致应变与电机转换稳定性的统一。本研究可以为无机导电填料的高分子刷可控包覆奠定理论基础，同时为高电致应变DEs的大规模制造提供新途径。

为克服目前介电弹性体材料难以兼具低模量、高介电常数、低介电损耗，从而制备低驱动电压下高电致应变与电-机转换稳定的介电弹性体，本项目将聚硅氧烷和聚多巴胺（PDA）改性的碳纳米管（MWCNTs）填充至硅橡胶中制备了复合材料。由于聚硅氧烷和粘附性强的PDA层的存在使得MWCNTs与硅橡胶基体间的相互作用力增强，其在硅橡胶中的分散性增强，从而获得了兼具高介电常数、低介电损耗的复合弹性体。同时，由于具有绝缘特性的聚硅氧烷和PDA层的存在，使得因MWCNTs团聚及相互搭接而产生的漏导电流现象得到缓解，从而使得复合材料的介电损耗较低，击穿场强较高，电机转换稳定性较强。当采用甲基三乙氧基硅烷改性MWCNTs后，其在硅橡胶中的分散性得到改善，当其含量为2.0 wt%时，复合物的介电常数达5.02，比纯硅橡胶提高了57%，且介电损耗和弹性模量与纯硅橡胶几乎相当。此外，对于PDA改性的MWCNTs和BaTiO3共填充的硅橡胶复合体系，当MWCNTs的含量达2 wt%时，能够实现的驱动应变最大，为7.015%（@13.9 kV/mm），较纯硅橡胶的1.487%（@18.4 kV/mm）提高了3.7倍。