Effect of aspect ratio on piezo-resistance properties of aligned multi-walled carbon nanotube polymer composites

Multi-walled carbon nanotubes (MWNTs) are actively used as reinforcing and electrical filler materials in composites owing to their superior electrical and mechanical performances. The electrical, mechanical, and piezoresistive performances of MWNT/polymer composites vary depending on the filler direction and aspect ratio (A/R). In this study, we fabricated MWNT/polymer composites with fillers aligned at different A/R. To prepare the aligned MWNT polymer composite with three different A/R, well dispersed MWNTs in the polymer matrix were applied continuous shear force in one direction by two-roll mill. Also, randomly oriented composites using same fillers were compared their mechanical, electrical, and piezoresistive properties to aligned composites. The aligned composite with the high A/R showed 6.03 times higher in elastic modulus and 17.4 times higher in electrical conductivity compared to the randomly oriented composite with the low A/R. The piezoresistance, expressed as the maximum resistance change in tension, of the aligned composite with the low A/ R had 84% higher than that of the randomly arrayed composite with the high A/R. In contrast to the enhancement of mechanical and electrical properties as the A/R rises and alignment occurs, the resistance in tension increases as the A/R decreases and the fillers are aligned. Thus, the influence of the filler alignment on the piezo-resistance properties of the composite is significant.