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

• Applicant: Dr.-Ing. Ulrike Staudinger
• Subject Area: Synthesis and Properties of Functional Materials
• Term: from 2015 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 268676966

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.

• DFG Programme: Research Grants