A Composite Fabrication Sensor Based on Electrochemical Doping of Carbon Nanotube Yarns

Abstract

This work shows evidence of conventional liquid and polymer molecules doping macroscopic yarns made up of carbon nanotubes (CNT), an effect that is exploited to monitor polymer flow and thermoset curing during fabrication of a structural composite by vacuum infusion. The sensing mechanism is based on adsorption of liquid/polymer molecules after infiltration into the porous fibers. These molecules act as dopants that produce large changes in longitudinal fiber resistance, closely related to the low density of carriers near the Fermi level of bulk samples of CNT fibers, reminiscent of their low‐dimensional constituents. A 25% decrease in fiber resistance upon exposure to electron–donor radicals formed during epoxy vinyl ester polymerization is shown as an example. At later stages of curing the matrix undergoes shrinkage and applies a compressive stress to the fibers. The resulting sharp increase in electrical resistance provides a mechanism for detection of the matrix gel point. The kinetics of resistance change during polymer ingress are related to established models for macromolecular adsorption, thus also enabling prediction of polymer flow. This is demonstrated for vacuum infusion of a 150 cm2 glass fiber laminate composite, with the CNT fiber yarns giving accurate prediction of macroscopic resin flow according to Darcy's law.

Surface Chemistry Analysis of Carbon Nanotube Fibers by X‐Ray Photoelectron Spectroscopy

“…The comparison of annealed with as‐made materials indicates that adsorbed species at the CNT fiber surface probably hybridize with the valence band states due to wave function overlap. This would imply that surface impurities can affect the optical and electronic properties of the constituent CNTs, and therefore bulk properties such as conductance and its dependence on dopants . Such impurities are also expected to have lower electrochemical stability than the CNTs and could thus be the origin of small pseudocapacitive contributions occasionally observed in low scan rate cyclic voltammetry.…”

Interlaminar toughening in structural carbon fiber/epoxy composites interleaved with carbon nanotube veils

“…It is worth noting that integration of CNT fiber veil, compared with electrospun thermoplastic fiber veil, would be more attractive since the former also endow the composite structure multifunctionalities (i.e. SHM [33]).…”

“…Second, CNT possess higher mechanical properties (tensile strength, Young's modulus et al) and larger specific surface area, thus enable to build a stronger mechanical link between the fracture surfaces. Last but not least, exceptional electrical (when metallic [31]) and thermal conductivity of CNT endow resultant composites multifunctionalities, such as prevention of unwanted electrostatic discharges, electromagnetic interference shielding or damage suppression during lightning strike and power management [32] as well as potential for damage sensing of hierarchical composites [33].…”

Graphene‐Coated Spandex Sensors Embedded into Silicone Sheath for Composites Health Monitoring and Wearable Applications

“…yarns, [6][7][8][9] 2D thin films, [10][11][12] or 3D selfsensing structures. [5,[13][14][15] Piezoresistive sensors have shown a great promise in sensing human movements, [16,17] heart rate monitoring and pulse measurement; [18,19] they have been used for applications in machine learning (e.g., in soft robotics [20,21] ), as well as real-time structural health monitoring (SHM) [22,23] and resin curing screening [22,24,25] in the structural parts and composites.…”