Waterproof Flexible Polymer-Functionalized Graphene-Based\nPiezoresistive Strain Sensor for Structural Health Monitoring and\nWearable Devices

Abstract

In recent times,\nflexible piezoresistive polymer nanocomposite-based\nstrain sensors are in high demand in wearable devices and various\nnew age applications. In the polymer nanocomposite-based strain sensor,\nthe dispersion of conductive nanofiller remains challenging due to\nthe competing requirements of homogenized dispersion of nanofillers\nin the polymer matrix and retaining of the inherent characteristics\nof nanofillers. In the present work, waterproof and flexible poly­(vinylidene\ndifluoride) (PVDF) with a polymer-functionalized hydrogen-exfoliated\ngraphene (HEG)-based piezoresistive strain sensor is developed and\ndemonstrated. The novelty of the work is the incorporation of polystyrene\nsulfonate sodium salt (PSS) polymer-functionalized HEG in a PVDF-based\nflexible piezoresistive strain sensor. The PSS-HEG provides stable\ndispersion in the hydrophobic PVDF polymer matrix without sacrificing\nits inherent characteristics. The electrical conductivity of the PVDF/PSS-HEG-based\nstrain sensor is 0.3 S cm^–1, which is two orders\nof magnitude higher than the PVDF/HEG-based strain sensor. Besides,\nnear the percolation region, the PVDF/PSS-HEG shows a maximum gauge\nfactor of 10, which is about two times higher than the PVDF/HEG-based\nflexible strain sensor and 5-fold higher than the commercially available\nmetallic strain gauge. The enhancement in the gauge factor is due\nto the stable dispersion of PSS-HEG in the PVDF matrix and electron\nconjugation caused by the adherence of negatively charged sulfonate\nfunctional groups on the HEG. The developed waterproof flexible strain\nsensor is demonstrated using portable wireless interfacing device\nfor various applications. This work shows that the waterproof flexible\nPVDF/PSS-HEG-based strain sensor can be a potential alternative to\nthe commercially available metallic strain gauge.