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.

Graphene nanoplatelet (GNP)/poly(methyl methacrylate) (PMMA) nanocomposite solution was spray coated on a glass fibre reinforced polymer composite (GFRP) beam with different initial electrical resistance (R 0 ). Scotch tape erosion method was used to tailor the R 0 of the sensors. Beams and the sensors were characterized by computed tomography (CT) and scanning electron microscopy (SEM) respectively. The piezoresistive behaviour of these sensors was evaluated in monotonic, step and cyclic loading conditions. These spray coated sensors offered good sensitivity (38.5 times) as compared to a strain gauge. A gauge factor (GF) of 55±0.5, 70±2, and 77±1 was obtained for R 0 of 1, 7 and 21 kΩ GNP layers, respectively. Sensors showed good response and stability under the step and cyclic loading conditions. The ease in the process of application coupled with good sensitivity demonstrates that the GNP/PMMA spray coated sensor can be a potential candidate for the futuristic multi-functional materials for structural health monitoring.

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