Abstract
This work demonstrates the application of electrospun single and bundled carbon nanofibers (CNFs) as piezoresistive sensing elements in flexible and ultralightweight sensors. Material, electrical, and nanomechanical characterizations were conducted on the CNFs to understand the effect of the critical synthesis parameter—the pyrolyzation temperature on the morphological, structural, and electrical properties. The mechanism of conductive path change under the influence of external stress was hypothesized to explain the piezoresistive behavior observed in the CNF bundles. Quasi-static tensile strain characterization of the CNF bundle-based flexible strain sensor showed a linear response with an average gauge factor of 11.14 (for tensile strains up to 50%). Furthermore, conductive graphitic domain discontinuity model was invoked to explain the piezoresistivity originating in a single isolated electrospun CNF. Finally, a single piezoresistive CNF was utilized as a sensing element in an NEMS flow sensor to demonstrate air flow sensing in the range of 5–35 m/s.
Highlights
Technological advancements made over the past few decades in soft material processing and nanofabrication techniques have led to substantial progress in the development of flexible and wearable sensors
Traditional piezoelectric materials like lead zirconate titanate (PZT), barium titanate, and zinc oxide have mainly been explored for developing sensors and energy harvesters in the past[1,2,3,4,5,6]
Various spectroscopic and microscopic characterization experiments including Raman, X-ray photoelectron spectroscopy (XPS), FESEM and Transmission electron microscopy (TEM) analyses were conducted to explain the early onset of piezoresistivity in relatively low temperature pyrolyzed electrospun PAN nanofiber bundles
Summary
Technological advancements made over the past few decades in soft material processing and nanofabrication techniques have led to substantial progress in the development of flexible and wearable sensors. Knight and White proposed an empirical understand the effect of different pyrolyzation temperatures on formula for the calculation of crystallite size (La) of the individual the microstructure, morphology, and electrical properties of graphitic crystals inside graphitic carbons and other sp2-bonded electrospun PAN-based CNFs. Various spectroscopic and microscopic characterization experiments including Raman, X-ray photoelectron spectroscopy (XPS), FESEM and TEM analyses were conducted to explain the early onset of piezoresistivity in relatively low temperature (compared to other works in literature) pyrolyzed electrospun PAN nanofiber bundles. Electrospun PAN nanofibers pyrolyzed at temperatures as low as 950 °C were used as piezoresistive sensing elements to demonstrate two distinct modes of operation involving single CNF and bundled CNFs. Ultralightweight and flexible strain sensors were demonstrated that use the conductive property of the electrospun CNF bundle combined with the effect of the change of its conductance path when subjected to external stress.
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