高电致形变介电弹性体的多层次结构调控、能量转换机理及应用

Development of dielectric materials with low drive voltage, large driven deformation, high drive response rate, and high energy density is of great significance. The key to improve the performance of dielectric elastomers is how to improve the energy density while deteriorating the mechanical properties and other dielectric properties as little as possible. The orientational polarization and energy density of elastomers can be efficiently enhanced by introducing strong polar organic groups into their chain structures. This project will prepare novel silicone rubber containing strong push-pull type azobenzene moieties on their chain structure; study the structure, properties and electromechanical deformation behaviors of this new type of dielectric elastomers. The relationship between the nature of hierarchical structure elements (molecular structure, loading, and orientation degree of the azobenzenes; crosslinking density and effective chain molecular weight of silicone rubber) and the performance of this new type elastomres (mechanical properties, electrical properties, electromechanical actuation behaviors) will be well understood to direct the preparation of advanced dielectric elastomer films. The electromechanical deformation performance will be further optimized by controlling the type, content, and orientation direction of the azobenzene groups. The prototype electromechanical actuation devices will also be developed based on this new type of elastomers. Efforts of this project are expected to offer a promising pathway to design advanced high performance dielectric elastomers as well as to understand the underlying operational mechanism of nanostructured electromechanical systems.

研究并开发具有低驱动电压、大驱动形变、高驱动响应速率、高能量密度的介电弹性体材料具有重要意义。提高介电弹性体电致形变性能的关键在于如何有效提高弹性体的能量密度而不劣化其他力学性质和电学性质。在分子链结构中引入强极性有机基团、制备全有机弹性体，能有效提高材料取向极化和能量密度。本项目拟制备含强极性偶氮苯基团的硅橡胶，将这类硅橡胶作为介电弹性体，系统研究其结构、性质、电致驱动形变行为等，建立偶氮苯化学结构与含量、取向态结构、硅橡胶交联密度及有效链分子量等多层次结构因素与该类弹性体力学性质、电学性质、电驱动形变性能之间的关系。通过控制偶氮苯基团类型、含量、取向方向以及硅橡胶的双峰网络结构等调控该类弹性体的电学性质、力学性质，综合提高力电耦合性能，得到一类性能优于目前研究水平的介电弹性体材料，并探索开发新型电驱动原型器件。本项目的实施将为研究和开发介电弹性体材料与器件提供新的思路。

开发具有高介电常数、低弹性模量的弹性体材料是实现高电致形变介电弹性体驱动器的关键。本项目设计、制备并表征了多种具有不同化学结构的弹性体材料，包括（1）由高分子量、低分子量预聚物共聚形成的双峰网络结构硅橡胶；（2）共价接枝强极性偶氮苯生色团的硅橡胶；（3）接枝极性不同偶氮苯生色团的硅橡胶；（4）物理掺杂偶氮苯生色团的热塑性聚氨酯；（5）硅橡胶/热塑性聚氨酯共混物；（6）高介电陶瓷纳米粒子填充的弹性体复合材料等。通过系统研究所得介电弹性体化学组成、微观结构、介电性质、力学行为、电驱动特性，获得了介电常数与弹性模量的解耦调控规律。有机物/弹性体复合体系较无机陶瓷/弹性体复合体系界面缺陷更少，有利于获得高绝缘强度、低弹性模量的弹性体。有机物/弹性体共混体系较共价接枝体系化学制备上简单，而在物理性质方面相差不大。优化的介电弹性体介电常数4.5，弹性模量约为35 kPa，断裂伸长率约300%，可提供约18%的电驱动应变，作为力电换能器收集电能时，可实现约0.8 mJ/cm3的电能收集能力。另外，在研究高性能介电弹性体过程中，我们认识到可伸缩柔性电极也是掣肘该类器件性能提高的瓶颈，进而发展了一类基于银纳米线与碳纳米管复合材料的柔性电极用于介电弹性体的驱动。对比通常采用的碳胶电极，这种新型复合电极可使驱动电场下降约50%。