Electrospun Poly(vinylidene fluoride) Nanocomposites with Ionic Liquid Functionalized Graphene Nanoplatelets by a Noncovalent Method for Piezoresistive Pressure Sensor Applications

Piezoresistive pressure sensors have been prepared by the electrospinning of poly(vinylidene fluoride) (PVDF) containing graphene nanoplatelets (GNP) functionalized using 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIM(OTf)) ionic liquid (IL). Optical microscopy demonstrated that the functionalized GNP powder presented particles with a smaller lateral size. The obtained mats were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, differential scanning calorimetry, electrical resistivity using two and four probes, and electromechanical testing with up to 32 load-unload cycles. Functionalization with BMIM(OTf) resulted in a higher PVDF electroactive phase. Electrospun mats obtained without the IL displayed a signal comparable to noise, while mats obtained with the BMIM(OTf) functionalized GNP displayed a clear signal, indicating that the IL helped with the dispersion of GNP on the PVDF matrix. Electrospun mats containing 1.0%m functionalized GNP presented the best performance among the evaluated samples, presenting low hysteresis and a lower distribution of the read values especially in the working range of 0 to 250 kPa. The piezoresistive behavior of the sample was tested under 32 load-unload cycles, remaining stable. Higher ranges of axial load resulted in the rupture of the fibers and swift degradation of the piezoresistive signal under a high number of cycles. A simple load cell was assembled to demonstrate the capacity of the membranes to act as piezoresistive compressive sensors capable of detecting the pressing of a human finger and differentiating between applied weights.