低渗流阈值超弹导电复合材料的制备及其在柔性压阻传感器中的应用

Flexible pizeoresistive pressure sensors show promising application in various fields, like e-skin, wearable medical monitoring devices and so on. In current piezoresistive sensors, sensing layer consists of the elastic deformable layer and surface conducting layer, which are used to sense and transform the pressure, respectively. However, the match of mechanical property between these two layers has not been solved till now, which would easily cause delamination between these two layers. This will further cause poor stability and short lifetime of the device. To address this issue, one layer of hyperelastic conducting composite material is proposed to transform the signal by itself, which is highly deformable and conductive. Base on percolation theory, Ni-NWs with large length to width ratio assembled on rGO is introduced into hyperelastic matrix with excellent hyperelasticity, and magnetic field is applied to manipulate their alignment and the distribution. In this way, low percolation threshold can be achieved and high conductivity can be obtained while the hyperelasticity of matrix is maintained. The novel single layer of sensing layer will be prepared by this method and the mismatch issue of the piezoresistive sensor can be solved. For now, the controllable preparation and alignment of Ni-NWs has been preliminarily achieved. Later on, systematic study will be performed on the mechanism of controlling assembled conductor alignment by magnetic field. And the influence of conductor on the performance of composite will be investigated in detail, including conductivity and so on. Combing the application of the composite in piezoresistive sensor and intensive study of the effect on its stability, this project will be very meaningful in obtaining high performance piezoresistive sensor and promoting them in real applications.

柔性压阻传感器在电子皮肤、可穿戴医疗监测等领域应用前景广阔。现有结构中敏感层包括弹性变形层和表面导电层两层材料，分别实现对压力的感应及传导。但目前还无法使这两层材料力学性能达到匹配，导致两层间极易剥离，影响器件稳定性及寿命。针对这一问题，本项目提出一种超弹导电复合材料作为单层敏感层，既易变形又导电可独立完成信号传递。通过引入渗流效应，在具有优异超弹性的基体中引入组装有rGO的大长径比磁性Ni-NWs，通过外磁场协同调控两者的排列及分布，实现超低渗流阈值，得到高电导率同时保持了基体超弹性，以此制备新型单层敏感层，从而解决现有压阻传感器中界面失配问题。目前，已初步实现纳米线结构的可控制备及在基体中的排列调控。后续，将系统研究磁场对导电相排列的调控机理及其分布、含量对复合材料电导率等性能的影响规律，结合在压阻传感器中的应用及对稳定性影响的深入研究，将对得到高性能压阻传感器及推广应用产生重要影响。

高灵敏度与良好的稳定性对柔性压阻传感器在电子皮肤、可穿戴医疗监测设备等领域的应用至关重要。而现有传统传感器敏感层包括弹性变形层和表面导电层两层材料，不但常用的表层导电层材料杨氏模量过高，载荷下变形困难，导致传感器灵敏度偏低，且两层材料力学性能悬殊，循环加载卸载过程使表面导电层易生成微裂纹甚至与变形层脱离，影响器件稳定性及寿命。针对这些难题，本项目提出超弹导电复合材料作为单层敏感层，既易变形又导电可独立完成信号传递有效避免两层材料力学性能悬殊引起的界面失配问题。利用外加磁场对引入超弹基体Ecoflex中Ni-NWs及与之结合rGO的排列进行协同调控，在所需方向对二者充分利用，实现低渗流阈值，同时基本保持了基体的低杨氏模量。其中Ni-NW采用液相还原方法在外磁场作用下合成了珠链状且具有可控直径(小至180nm)和长径比L/D达到300的珠链状结构Ni-NWs，系统研究了还原剂、外加磁场等因素对Ni纳米颗粒与纳米线形成的控制机理，并探索了磁场作用下Ni-NWs在高黏度基体中的转向机理，系统研究了复合导电相Ni-NWs-rGO体积含量及空间排列对复合材料渗流阈值、电导率及杨氏模量的影响，并揭示复合材料的导电机制及压力传导机制，实现了在超低渗透阈值(0.27vol％)下达到了0.003S/m的高电导率、71.8％高透过率以及122.8kPa低杨氏模量的复合压敏材料。结合利用COMSOL Multiphysics优化获得的高性能传感器结构参数，以该压敏材料作为制造压阻传感器的单层敏感层，以经济高效热压印技术获得的大面积微半球作为模板，构造了大尺寸高性能显示出1302.1kPa-1优异平均灵敏度的压阻传感器，而传感器之间的偏差仅为3.74％，稳定性与一致性良好。本项目形成了可控制备Ni-NWs、超弹导电复合材料、热压印微观结构，进而对压阻传感器性能实现调控的理论体系，为实现高稳定性及寿命的压阻传感器奠定理论基础，为实现透明，高灵敏度和大面积电子皮肤及可穿戴医学传感器提供了一种新途径。