Thermo- and chemo-electrical behaviour of carbon nanotube filled co-continuous conductive polymer nanocomposites (CPC) t
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Thermo- and chemo-electrical behaviour of carbon nanotube filled co-continuous conductive polymer nanocomposites (CPC) to develop amperometric sensors
Jianbo Lu, Mickaël Castro, Bijandra Kumar and Jean-François Feller Materials Engineering Laboratory of Brittany (LIMATB), European University of Brittany (UEB), South-Brittany, Lorient, FRANCE
ABSTRACT The conductive polymer nanocomposite (CPC) of multiwall carbon nanotubes (MWNT) filled Polycaprolactone (PCL) was formulated by melt mixing method. PCL based conductive phase served as disperse phase, blended with polypropylene (PP) and polyamide 12 (PA12) respectively. The thermo- and chemo-electrical properties of mono- and bicomponent CPC have been investigated independently. Results show that PP/PCL-CNT CPC is a good temperature sensor whereas no significant response was observed while exposing it to toluene vapor. In contrast, PA12/PCL-CNT exhibits good vapor sensing capability and few sensitivity to temperature variations. It is assumed that PP phase prevents the diffusion of vapor molecules within PCL conductive phase whereas vapor sensing results indicate that PP external matrix provides the CPC with higher barrier effects than PA12. INTRODUCTION The development of electrically conductive polymer nanocomposites (CPC) [1] has attracted a lot of attention in the last decade due to their variety of application such as self regulated heating [2] or vapour sensing [3]. CPC heterogeneous by nature, combine the insulting character of the polymer matrix and the high level of electrical conductivity of carbon nanofillers. At suitable composition CPC can be sensitive to their environment, essentially temperature [4], vapour [5], and strain [6]. Their response is characterized by a change in resistivity upon exposure to heat or organic vapours, leading respectively to the so called positive temperature coefficient effect (PTC) [7] or positive vapour coefficient effect (PVC) [8]. By reviewing the literature, the PTC effect is due to the volume expansion of the polymer matrix while heating, by which disturbs the conductive paths, leading to an increase in resistivity [9]. When the temperature is above the melting point of polymer, a decrease in resistivity is probably observed. This phenomenon is referred as negative temperature coefficient (NTC) [10]. It is believed that for semi-crystalins based CPC nanocpmposites, the conductive fillers migrated into new amorphous phase which is initially crystalline phase, the destroyed network can be reestablished again causes a decrease in resistivity. The morphology and composition [11] of composites are believed to influence the PTC effect. Concerning the PVC effect, it is believed that diffusion of gas or vapor molecules throughout the polymer matrix, leading the swelling of the matrix polymer increased inter-filler gaps and eventually damages the inter-conduction networks in the composites. In this study, employing PP and PA12 as external matrix, the thermo- and chemo-electrical properties of two different cocontinu
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