Sensing of large strain using multiwall carbon nanotube/segmented polyurethane composites

Abstract

Multiwall carbon nanotube (MWCNT)/elastomeric composite films were fabricated using two segmented polyurethanes: an in-house synthesized one (SPU) and a commercial medical grade one (Tecoflex V R , TF). Electrical, mechanical, and electromechanical (piezoresistive) properties of both composites were evaluated as a function of the MWCNT weight concentration (1-10 wt %). An increase in electrical conductivity for both types of polymers was observed for MWCNT concentrations as low as 1 wt %. The electrical conductivity of MWCNT/TF composites was higher than that achieved for MWCNT/SPU composites. Mechanical properties of 8 wt % MWCNT/SPU composites showed a threefold increase in stiffness compared to neat SPU. The changes in electrical resistance of the composites showed higher sensitivity to strain for lower MWCNT concentrations. The piezoresistive signal of the composites allows to measure strains up to $400% before electrical depercolation occurs. The strain at which electrical depercolation occurs depends on the conductivity of the composite in its unloaded state. This kind of composites may find sensing applications in prosthetics, biomedical devices, and smart textiles.

Mechanical vs. electrical hysteresis of carbon nanotube/styrene–butadiene–styrene composites and their influence in the electromechanical response

“…These gauge factor can be tailored by changing CNT concentration or applied pre-stress to the composite, in order to obtain sensors with tailored sensibility [7]. Commercial metallic strain gages present gauge factors around 2 and are able to measure low deformations [8]. The gauge factor of CNT/polymer composites with different CNT type and polymer matrix allow a wide range of GF, between 0.74 and 50 [9] and also the development of small and large strain sensors [8].…”

“…Commercial metallic strain gages present gauge factors around 2 and are able to measure low deformations [8]. The gauge factor of CNT/polymer composites with different CNT type and polymer matrix allow a wide range of GF, between 0.74 and 50 [9] and also the development of small and large strain sensors [8]. The piezoresistive response, depends on parameters related to CNT conductivity, surface characteristics and dispersion on polymer matrix, the gauge factor being larger for filler concentrations in the composite near the percolation threshold [9].…”

“…The piezoresistive response, depends on parameters related to CNT conductivity, surface characteristics and dispersion on polymer matrix, the gauge factor being larger for filler concentrations in the composite near the percolation threshold [9]. Piezoresistive composites with thermoplastics or thermosetting polymer matrixes have been most often studied than elastomeric composites [8]. To development piezoresistive sensors with large deformation (up to 50% [10]) or tactile sensitive sensors, thermoplastic elastomers (TPE) are a promising material as they combine the mechanical properties of vulcanized rubbers (elastic recovery after large applied deformations) with the simple processability and recyclability of thermoplastics [11].…”

Covalent functionalization of single-walled carbon nanotubes through attachment of aromatic diisocyanate molecules from first principles

“…PU/CNT hybrid composites can be used as electromagnetic interference shielding materials [20] and new shape-memory materials [21]. They can also be used in biomedical devices with piezoresistive properties [18] and for tissue engineering scaffolds with nanostructured surface topography [22]. MWCNT-reinforced thermoplastic polyurethane nanocomposites have been reported to exhibit better thermal stability and mechanical performance [15].…”

“…Their versatile properties depend on the ratio of the flexible (polyol) and hard (diisocyanate) segments, but they still suffer from low electrical conductivity [18] and low mechanical strength [19]. PU/CNT hybrid composites can be used as electromagnetic interference shielding materials [20] and new shape-memory materials [21].…”