RESUMO
The demand for self-powered, flexible, and wearable electronic devices has been increasing in recent years for physiological and biomedical applications in real-time detection due to their higher flexibility and stretchability. This work fabricated a highly sensitive, self-powered wearable microdevice with Poly-Vinylidene Fluoride-Tetra Fluoroethylene (PVDF-TrFE) nano-fibers using an electrospinning technique. The dielectric response of the polymer was improved by incorporating the reduced-graphene-oxide (rGO) multi-walled carbon nano-tubes (MWCNTs) through doping. The dielectric behavior and piezoelectric effect were improved through the stretching and orientation of polymeric chains. The outermost layer was attained by chemical vapor deposition (CVD) of conductive polymer poly (3,4-ethylenedioxythiophene) to enhance the electrical conductivity and sensitivity. The hetero-structured nano-composite comprises PVDF-TrFE doped with rGO-MWCNTs over poly (3,4-ethylenedioxythiophene) (PEDOT), forming continuous self-assembly. The piezoelectric pressure sensor is capable of detecting human physiological vital signs. The pressure sensor exhibits a high-pressure sensitivity of 19.09 kPa-1, over a sensing range of 1.0 Pa to 25 kPa, and excellent cycling stability of 10,000 cycles. The study reveals that the piezoelectric pressure sensor has superior sensing performance and is capable of monitoring human vital signs, including heartbeat and wrist pulse, masticatory movement, voice recognition, and eye blinking signals. The research work demonstrates that the device could potentially eliminate metallic sensors and be used for early disease diagnosis in biomedical and personal healthcare applications.
RESUMO
The demand for highly flexible and self-powered wearable textile devices has increased in recent years. Graphene coated textile-based wearable devices have been used for energy harvesting and storage due to their outstanding mechanical, electrical and electronic properties. However, the use of metal based nanocomposites is limited in textiles, due to their poor bending, fixation, and binding on textiles. We present here reduced graphene oxide (rGO) as an n-type and conductive polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as a p-type material for a wearable thermoelectric nanogenerator (TEG) using a (pad-dry-cure) technique. We developed a reduced graphene oxide (rGO) coated textile-based wearable TEG for energy harvesting from low-grade human body heat. The conductive polymer (PEDOT:PSS) and (rGO) nanocomposite were coated using a layer by layer approach. The resultant fabric showed higher weight pickup of 60-80%. The developed textile based TEG device showed an enhanced Seebeck coefficient of (25-150 µV K-1), and a power factor of (2.5-60 µW m-1 K-1). The developed TE device showed a higher potential to convert the low-grade body heat into electrical energy, between the human body temperature of (36.5 °C) and an external environment of (20.0 ± 5 °C) with a temperature difference of (2.5-16.5 °C). The wearable textile-based TEG is capable of producing an open circuit output voltage of 12.5-119.5 mV at an ambient fixed temperature of (20 °C). The rGO coated textile fabric also showed reduced electrical sheet resistance by increasing the number of dyeing cycles (10) and increased with the number of (20) washing cycles. The developed reduced graphene oxide (rGO) coated electrodes showed a sheet resistance of 185-45 kΩ and (15 kΩ) for PEDOT:PSS-rGO nanocomposites respectively. Furthermore, the mechanical performance of the as coated textile fabric was enhanced from (20-80 mPa) with increasing number of padding cycles. The thermoelectric performance was significantly improved, without influencing the breath-ability and comfort properties of the resultant fabric. This study presents a promising approach for the fabrication of PEDOT:PSS/rGO nano-hybrids for textile-based wearable thermoelectric generators (TEGs) for energy harvesting from low-grade body heat.