Structural and Electromechanical insights into Thermoplastic Polyurethane/3D Hybrid Carbon Nanocomposites towards Strain Sensor Applications

Incorporation of different dimensional carbon allotropes within elastomeric matrices has been established as an effective strategy to fabricate functional conductive polymer nanocomposites (PNC). In this work, a higher dimensional 3D hybrid carbon nanofillers - comprising the synergistically integrated multi-walled carbon nanotubes immobilized into few-layers graphene – were incorporated into thermoplastic polyurethane (TPU) matrix, to demonstrate its effectiveness as a strain sensor. The conductive films fabricated through a simple solution casting technique, in which the mechanical, electrical and strain sensing characteristics are studied in view of filler’s distribution, structural confinement, and interfacial interactions. Analyses using wide-angle X-ray scattering, Raman spectroscopy, and tensile testing, revealed a higher degree of filler reinforcement within TPU moieties, indicating the pronounced interfacial interactions. Further, the tensile modulus heightened significantly with filler loading above their percolation threshold (363% for 20wt% loading). The structural features of dispersed filler aggregates were explored through an iterative model fitting of the ultra-small angle X-ray scattering (USAXS) data, along with scanning electron microscopy (SEM). As a strain sensor, the films displayed a superior working-strain Gauge Factor (GF=123), with an exceptional stability under both unidirectional and cyclic strain. Further, a large strain GF of 601.5 was evidenced for the composites with higher 3D filler loading. The findings provide a fundamental understanding, alongside validating the potential of hybrid carbonaceous fillers for the fabrication of PNCs with futuristic applications.