Tough and flexible styrene-butadiene block copolymers with defined carbon-based nanofillers for electrical and sensing applications

该项目的目标是开发基于韧性和柔性的丁苯嵌段共聚物(BCP)和碳纳米管(CNTs)的功能纳米复合材料，适用于电气和传感应用。本研究以第一个课题中所研究的BCP/CNT纳米复合材料为基础。它们在碳纳米管含量为~1 mA%的情况下就表现出了很高的导电性，同时保持了BCP的纳米结构和非凡的机械性能。为了实现碳纳米管在纳米尺度的BCP相中的最佳分散和局域化，从而在低碳纳米管含量时进一步提高导电性，使用了强烈缩短的碳纳米管。通过球磨机或微流控涡流装置的特殊激光处理，可以实现500~80 nm的不同粒度。用PS基团对碳纳米管进行改性，可以增强填料与PS相之间的相互作用，支持碳纳米管在PS相中或在两相界面上的分散和选择性排列。通过溶液混合和熔融混合制备了BCP复合材料，并定义了其形貌，并通过后续回火可重复地调整其形貌。分析了碳纳米管的尺寸分数(临界碳纳米管长度)和化学官能化对碳纳米管的形貌、电性能和力学性能的影响。此外，利用适用于高韧性聚合物材料的基本断裂功概念，对所选材料的缺口试件进行了断裂力学研究，并利用断裂功的基本概念评估了断裂韧性。通过测量复合材料在单轴拉伸和粘弹性范围内的变形诱导电阻变化，对导电BCP/CNT复合材料的压阻行为进行了表征。对于作为变形传感器的应用，高压阻灵敏度(高规因数)的调整和大变形范围内随变形变化的高线性度以及循环传感测量的良好重复性是决定性的。这些性质由基质聚合物的延展性和碳纳米管网络的密度和规律性决定。目的是了解碳纳米管的浓度和修饰对BCP中填充网络性能的影响及其对复合材料压阻行为的影响，以便能够调整复合材料的性能，使其应用于变形传感领域。

The aim of the project is the development of functional nanocomposites based on tough and flexible styrene-butadiene block copolymers (BCPs) with carbon nanotubes (CNTs) suitable for electrical and sensing applications. The nanostructured BCP/CNT composites with modified nanofillers, which were comprehensively investigated in the first project, are used as a basis for this study. They exhibit a high electrical conductivity already at low CNT contents of ~ 1 Ma% while retaining the nanostructure and the extraordinary mechanical property profile of the BCPs. To achieve an optimal dispersion and localization of the CNTs in the nm-scaled BCP phases and thus to further increase the electrical conductivity at low CNT contents, strongly shortened CNTs are used. Different size fractions from 500 nm to 80 nm are realized by shortening in a ball mill or by a special laser treatment with a microfluidic vortex flow device. A modification of the CNTs with PS groups should increase the interaction between filler and PS phase in the BCP and support the dispersion and selective arrangement of the CNTs in the PS phase or at the interface of both phases. The BCP composites are prepared by solution mixing and melt mixing and the morphologies are defined and reproducibly adjusted by subsequent tempering. The influence of the size fractions used (critical CNT lengths) and the chemical functionalization of the CNTs on the morphology and the electrical and mechanical properties are analyzed. In addition, fracture mechanical investigations are carried out on notched test specimens of selected materials with evaluation of the crack toughness by using the Essential Work-of-Fracture concept, which is suitable for highly ductile polymer materials.The characterization of the piezoresistive behavior of electrically conductive BCP/CNT composites is carried out by measuring the deformation-induced resistance change during the uniaxial tensile test and in cyclic hysteresis tests in the viscoelastic range of the composites. For the application as deformation sensors, the adjustment of a high piezoresistive sensitivity (high gauge factor) and a high linearity of the deformation-dependent resistance change within a wide deformation range as well as a good repeatability of the measurement with cyclic sensing are decisive. These properties are governed by the ductility of the matrix polymer and the density and regularity of the CNT network. The aim is to understand the influence of the CNT concentration and the CNT modification on the properties of the filler network in the BCP and its effects on the piezoresistive behavior of the composites in order to be able to adjust the properties of the composites for applications in the field of deformation sensing.