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苯乙烯-丁二烯嵌段共聚物（bcp）与碳纳米管（CNTs）的功能性纳米复合材料，适用于电气和传感应用。本研究以第一个项目中已全面研究的改性纳米填料的纳米结构BCP/CNT复合材料为基础。它们在低碳纳米管含量（~ 1 Ma%）时已经表现出高导电性，同时保留了bcp的纳米结构和非凡的机械性能。为了在纳米尺度的BCP相中实现碳纳米管的最佳分散和局部化，从而在低碳纳米管含量下进一步提高电导率，使用了强缩短的碳纳米管。通过球磨机的缩短或微流体涡旋装置的特殊激光处理，可实现500 ~ 80 nm的不同粒度馏分。用PS基团修饰CNTs应增加填料与BCP中PS相之间的相互作用，并支持CNTs在PS相或两相界面上的分散和选择性排列。通过溶液混合和熔体混合制备了BCP复合材料，并通过随后的回火确定了形貌并可重复调整。分析了所使用的碳纳米管尺寸分数（临界碳纳米管长度）和碳纳米管的化学功能化对形貌和电学和力学性能的影响。此外，采用适用于高延展性高分子材料的基本断裂功概念，对选定材料的缺口试样进行断裂力学研究，评价其裂纹韧性。通过测量导电BCP/CNT复合材料在单轴拉伸试验和粘弹性循环迟滞试验中变形引起的电阻变化，对复合材料的压阻性能进行了表征。对于作为变形传感器的应用，在宽变形范围内调整高压阻灵敏度（高测量因子）和变形相关电阻变化的高线性以及循环传感测量的良好重复性是决定性的。这些性能是由基体聚合物的延展性和碳纳米管网络的密度和规则性决定的。目的是了解碳纳米管浓度和碳纳米管改性对BCP中填料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以用于变形传感领域。

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.