Polymer/carbon nanotube (CNT) composites show next to improved mechanical, thermal, and electrical properties also sensitivity to external stimuli. A detection of environmental condition changes is possible, if it affects the electrically conductive CNT network inside the insulating polymer matrix. In case of liquid sensing, swelling of the polymer matrix due to contact with organic liquids and interactions between solvent molecules and CNTs result in a local gap enlargement between individual CNTs and/or CNT clusters, resulting in a detectable increase of electrical resistance. Accordingly, CNT based conductive polymer composites (CPCs) represent very promising candidates for the design of smart components capable of integrated monitoring. In this presentation we focus on their use as leakage detectors for organic solvents.
The sensor concept, as well as the underlying mechanism, is demonstrated for polycarbonate (PC)/CNT based CPCs on compression-molded samples. The selectivity as an important sensor property will be discussed in context with the Hansen solubility parameters and the solvent molecule’s size. The time dependent electrical response characteristic upon immersion depends on the diffusion kinetics of the specific solvent molecules into the CPC. A model allowing the calculation of the time dependent relative resistance (Rrel) change is presented considering several factors like the diffusion parameters, composite characteristics like initial resistance and geometrical values of the sensing sample. Using this model, Rrel curves of PC/MWCNT composites were simulated which fit very well the experimental data.
In order to examine the production of first prototype large area sensors, fibers and textiles based on composites of different polymer matrices with multi-walled carbon nanotubes (MWCNT) were produced. MWCNT containing fibers based on poly lactic acid (PLA) and polycaprolactone (PCL)/ polypropylene (PP) blends were produced by melt spinning and textile fabrication was performed for PCL/PLA blends. For all presented composite systems the electrical response characteristics was analyzed for various organic solvents.