A loofah-like carbon nanotube–Ag structure (LOOCAS) enabling piezoresistive transient sensing of dynamic strain and impulse load

Abstract

This work demonstrates a flexible piezoresistive transient sensor based on a loofah-like carbon nanotube–Ag structure (LOOCAS) that enables feasible detection of dynamic strain and vertical impulse load. The LOOCAS is realized through the controlled infiltration of an ionic Ag ink into the vertically aligned carbon nanotube (CNT) forest, followed by its thermal reduction into Ag nanoparticles, creating intimate CNT–Ag electrical contacts as well as ample micropores in between the CNT–Ag structure. Fabricable by this simple and scalable process, the LOOCAS can not only possess the fortified electrical pathways via numerous CNT–Ag contacts but also form a microporous architecture beneficial for mechanical sensing via capillary-induced sub-millimeter-scale deformation. With the underpinnings of discrete Ag nanoparticle formation preferentially at defect sites on CNTs, we investigate two prime design parameters, the ionic Ag ink concentration and CNT forest length, to optimize the density and size of the Ag nanostructure and to regulate the microporous electrical pathways. The optimized LOOCAS device, encapsulated by an elastomeric polymer, exhibits clean and easily detectable transient outputs, reaching a maximum ΔR/R₀ of more than 30 000 at 30% tensile strain with sharp peaks at both strain and recovery, and shows a monotonic strain-dependent increase in response. The LOOCAS also generates distinct, intensity-resolved peaks upon vertical tapping impacts, confirming multidirectional transient electromechanical transduction within a durable form factor. We further propose a tiled aerospace smart-skin concept in which flexible and scalable LOOCAS patches are conformally distributed over the wings and fuselage of aircraft (e.g., UAV) to instantly isolate subtle contact events and flow-transition-induced vibrations.