Waterproof Flexible Polymer-Functionalized Graphene-Based Piezoresistive Strain Sensor for Structural Health Monitoring and Wearable Devices

Abstract

In recent times, flexible piezoresistive polymer nanocomposite-based strain sensors are in high demand in wearable devices and various new age applications. In the polymer nanocomposite-based strain sensor, the dispersion of conductive nanofiller remains challenging due to the competing requirements of homogenized dispersion of nanofillers in the polymer matrix and retaining of the inherent characteristics of nanofillers. In the present work, waterproof and flexible poly(vinylidene difluoride) (PVDF) with a polymer-functionalized hydrogenexfoliated graphene (HEG)-based piezoresistive strain sensor is developed and demonstrated. The novelty of the work is the incorporation of polystyrene sulfonate sodium salt (PSS) polymer-functionalized HEG in a PVDF-based flexible piezoresistive strain sensor. The PSS-HEG provides stable dispersion in the hydrophobic PVDF polymer matrix without sacrificing its inherent characteristics. The electrical conductivity of the PVDF/PSS-HEG-based strain sensor is 0.3 S cm −1 , which is two orders of magnitude higher than the PVDF/HEG-based strain sensor. Besides, near the percolation region, the PVDF/PSS-HEG shows a maximum gauge factor of 10, which is about two times higher than the PVDF/HEG-based flexible strain sensor and 5-fold higher than the commercially available metallic strain gauge. The enhancement in the gauge factor is due to the stable dispersion of PSS-HEG in the PVDF matrix and electron conjugation caused by the adherence of negatively charged sulfonate functional groups on the HEG. The developed waterproof flexible strain sensor is demonstrated using portable wireless interfacing device for various applications. This work shows that the waterproof flexible PVDF/ PSS-HEG-based strain sensor can be a potential alternative to the commercially available metallic strain gauge.

Waterproof Graphene-PVDF Wearable Strain Sensors for Movement Detection in Smart Gloves

“…In fact, it is demonstrated that the percolation threshold θ c of the obtained samples is achieved at a GNP weight fraction around 0.55% wt. This value is lower with respect to the one recently observed in case of hydrogen exfoliated graphene in a PVDF polymer matrix [26], and is comparable with the one obtained using CNTs as nanofillers [34]. Furthermore, it is worth noting that the perfect integration of GNPs inside the polymer matrix among an optimum dispersion of them, without agglomerations or defects, allowed us to reach electrical conductivity values one or two order of magnitudes higher than the ones of PVDF nanocomposites filled with other graphene-based nanofillers, such as reduced graphene oxides [13], CNTS [27], and hydrogen exfoliated graphene [26].…”

“…Due to their outstanding properties, GNP-filled polymer composites have been widely investigated in various engineering applications, including electromagnetic compatibility [ 18 , 19 , 20 ], structural sensing and monitoring [ 21 , 22 , 23 , 24 ]. Different polymer matrices have been explored, such as polystyrene [ 17 , 20 ], epoxy-based vinyl ester resins [ 18 , 19 , 24 ], polydimethylsiloxane [ 5 , 22 ], polyurethane [ 25 ], and polyvinylidene fluoride (PVDF) [ 23 , 24 , 26 , 27 , 28 ]. Among them, PVDF is garnering ever growing interest for sensing applications owing to its uncommon chemical resistance and thermal mechanical physical properties, including piezoresistive and piezoelectric ones [ 29 , 30 ].…”

“…Among them, PVDF is garnering ever growing interest for sensing applications owing to its uncommon chemical resistance and thermal mechanical physical properties, including piezoresistive and piezoelectric ones [ 29 , 30 ]. Moreover, the hydrophobic features of PVDF are crucial for the realization of self-cleaning anti-biofouling waterproof sensors [ 26 ]. Hence, several studies reported on the improvement of electric, mechanical and electromechanical properties of PVDF composites by the combination of carbonaceous nanofillers [ 31 , 32 , 33 , 34 ].…”

“…Despite that, the electromechanical properties of PVDF composites loaded with different GNP loading concentrations have not been deeply studied. In fact, to the best of the authors’ knowledge, only a few publications deal with such properties of PVDF nanocomposites, most of them using different graphene-based nanostructures as fillers, such as carbon fibers or nanotubes [ 13 , 26 , 27 , 34 ]. For instance, P. Costa et al investigated the piezoresistive behavior of PVDF-based composites filled with graphene oxide and single wall CNTs [ 13 , 34 ].…”

“…For instance, P. Costa et al investigated the piezoresistive behavior of PVDF-based composites filled with graphene oxide and single wall CNTs [ 13 , 34 ]. More recently, the influence of polymer functionalization of hydrogen exfoliated graphene has been assessed with the aim of providing a stable dispersion in the PVDF polymer matrix [ 26 ], while the possibility to tune the piezoresistive properties of PVDF/CNT composite through the addition of poly methyl methacrylate has been demonstrated in [ 27 ].…”