Gekoppelte elektrische und rheologische Messungen an leitfähigen Polymerkompositen in Dehnung
Zusammenfassung der Projektergebnisse
The research project was focused on the rheological and electrical behaviour of conductive polymer composites containing carbon black or carbon fibres. In order to describe relationships between defined mechanical deformation and structure development in the composites, simultaneous electrical and rheological experiments in shear and in elongation were performed. It was found that the applied shear stress is a decisive parameter affecting the structure development in the conductive polymer composites. The critical stress at which the flow-induced destruction of conductive particle structures prevails over the flow-induced and thermally driven build-up effects can be determined from the simultaneous amplitude sweep measurements. This critical stress increases linearly with the filler concentration. The stability of composite structure is also determined by strength of particle-particle interactions. It was found that the critical shear stress of composites containing microfiller (carbon fibres) is considerably lower than that of composites with nanoparticles (carbon black). The behaviour of conductive composites under stresses above the critical level was investigated by simultaneous time sweeps at different frequencies and, thus, at different deformation amplitudes. The experiments showed that at sufficiently low deformation amplitudes the particles forming the conductive path rearrange themselves in shear direction without interruption of the particle-particle interactions. At higher deformation amplitudes the contacts between particles are interrupted, the particle structures lose their ability to transfer electrons and the electrical resistance of the composite sample increases steeply. In this initial period of oscillatory shear flow-induced destruction is the dominant process. However, it was found that at long experimental times a dynamic equilibrium between flow-induced destruction and build-up is established. A simple model describing the electrical behaviour of the composites in the equilibrium state under oscillatory shear was proposed. To study the influence of the shear stress in more detail, simultaneous creep experiments were performed as well. As expected with increasing shear stress applied the number of destroyed conductive pathways increases. However, pronounced rebuilding effect was observed at longer creep times, the rate of which is markedly higher than in the case of build-up process under quiescent conditions. It was also found that the deformation history of the material affects its electrical behaviour under shear considerably. The material containing particle structures formed during the shear showed higher resistance against flow-induced destruction of conductive pathways compared to the material with equal electrical conductivity but containing particle structures formed under quiescent conditions. The influence of the incorporation of conductive fillers on the rheological properties of the composites in elongation was determined. It was found, that the flow-induced destruction of the particle structures in the composites above percolation threshold leads to a considerable decrease in the elongational viscosity. In order to investigate this finding in more detail, the Münstedt tensile rheometer was successfully modified in the way, which allows one to measure the direct current conductivity simultaneously with the elongation. First results obtained from these unique measurements, not reported in the literature up to now, show that the electrical conductivity reacts very sensitively on the elongational deformation of the composites melts.
Projektbezogene Publikationen (Auswahl)
- Oscillations of the electrical resistance induced by shear deformation in molten carbon black composites. Polymer (2013), 54 (3), 1106-1113
Krückel J., Stary Z., Schubert D.W.
(Siehe online unter https://doi.org/10.1016/j.polymer.2012.12.051) - Rheology and conductivity of carbon fibre composites with defined fibre lengths. Compos. Sci. Technol. (2013), 85, 58-64
Stary Z., Krückel J., Week C., Schubert D.W.
(Siehe online unter https://doi.org/10.1016/j.compscitech.2013.06.006) - Shear induced electrical behaviour of conductive polymer composites. AlP Conference Proceedings (2013), 1526, 258-267
Stary Z., Krückel J., Schubert D.W.
(Siehe online unter https://dx.doi.org/10.1063/1.4802620) - Electrical conductivity of carbon black-based polymer composites under creep in the molten state. Polymer (2014), 55, 3980-3986
Stary Z„ Krückel J„ Schubert D.W.
(Siehe online unter https://doi.org/10.1016/j.polymer.2014.06.047) - Simultaneous Electrical and Rheological Measurements on Molten Conductive Polymer Composites under Elongation. Polymer (2014), 55 (22), 5608-5611
Stary Z.
(Siehe online unter https://doi.org/10.1016/j.polymer.2014.09.028) - Theoretical and experimental study of the dynamic percolation behaviour of carbon black filled polymethylmethacrylate prior and after shear - A novel three phase approach. Eur Polym J (2014), 53, 50-57
Krückel J., Schubert D.W.
(Siehe online unter https://doi.org/10.1016/j.eurpolymj.2014.01.011) - Electrical conductivity and rheology of carbon black composites under elongation. AlP Conference Proceedings (2015), 1662, 040001-1-040001-7
Stary, Z.
(Siehe online unter https://doi.org/10.1063/1.4918889) - Phase structure, rheology and electrical conductivity of co-continuous polystyrene/polymethylmethacrylate blends filled with carbon black Compos. Sci. Technol. (2015), 119, 138-147
Scherzer S., Pavlova E., Esper J., Stary Z.
(Siehe online unter https://doi.org/10.1016/j.compscitech.2015.10.003)
