Tobias Villmow

Liquid sensing: smart polymer/CNT composites

Today polymer/carbon nanotube (CNT) composites can be found in sports equipment, cars, and electronic devices. The growth of old and new markets in this area has been stimulated by our increased understanding of relevant production and processing methods, as well as the considerable price reduction of industrial CNT grades. In particular, CNT based electrically conductive polymer composites (CPCs) offer a range of opportunities because of their unique property profile; they demonstrate low specific gravity in combination with relatively good mechanical properties and processability. The electrical conductivity of polymer/CNT composites results from a continuous filler network that can be affected by various external stimuli, such as temperature shifts, mechanical deformations, and the presence of gases and vapors or solvents. Accordingly, CNT based CPCs represent promising candidates for the design of smart components capable of integrated monitoring. In this article we focus on their use as leakage detectors for organic solvents.

Investigation of liquid sensing mechanism of poly(lactic acid)/multi-walled carbon nanotube composite films

The liquid sensing mechanism of melt-processed poly(lactic acid) (PLA)/multi-walled carbon nanotube (MWNT) composite films was investigated for the influence of MWNT loading, solubility parameters of solvents used, solvent transport behaviours, resultant electrical resistance changes, as well as crystallization of the PLA matrix. The diffusion, sorption and permeation coefficients of neat PLA and the composites were estimated, indicating that MWNT network structures block solvent molecules from penetrating into the polymer matrix. Solvent-induced crystallization of the polymer matrix was observed. Isothermally crystallized composites showed reduced resistances, a significant decrease of sorbed solvent content and a reduction of the resulting resistance changes on the solvent contact. In the context with sensing results on MWNT mats, it was proposed that the liquid sensing mechanism of PLA/MWNT composites consists of the overall electrical resistance changes caused by the structural variation of the conductive MWNT network in the polymer matrix and additional interactions between the MWNT and solvent molecules.

Influence of material and processing parameters on carbon nanotube dispersion in polymer melts

Abstract: Melt processing of polymer–carbon nanotube (CNT) composites is of great industrial importance for the large-scale production of composite materials and desired products. The properties of these composites greatly depend on the quality of CNT dispersion. In this chapter, a broad overview of the influence of material and processing parameters on the dispersion of multi-walled CNTs in thermoplastic polymer matrices during melt processing is provided. The results discussed here are based on small-scale batch mixers as well as on laboratory-scale continuous extruders. To analyse and quantify the state of dispersion, microscopic methods were applied.

Quantification of dispersion and distribution of carbon nanotubes in polymer composites using microscopy techniques

Abstract: Different stereological approaches have been applied to micrographs of light microscopy and transmission electron microscopy to estimate the degree of carbon nanotube dispersion in polymer composites at different length scales. Quantitative information about the spatial relationships between individual carbon nanotubes has been obtained by means of the spherical contact distribution function and a Boolean fibre model. The correlation function has been used to gain an orientation factor as a measure of carbon nanotube alignment. The corresponding theoretical foundations and suitable digital image processing techniques are introduced and illustrated with some specific examples.