Dual‐layer nanotube‐based smart skin for enhanced noncontact strain sensing

Abstract

The remarkable optical properties of single-walled carbon nanotubes suggest their use as nanoscale strain sensors. To help implement this idea as a practical technology, we have devised a new dual-layer strain-sensing smart skin. A submicron thick sensing layer of dilute, individualized nanotubes in poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) polymer is deposited onto the substrate to be monitored and then overcoated with a transparent protective polymer layer. Subsequent substrate strains are transmitted to the nanotubes, altering their semiconducting band gaps and causing systematic shifts in their characteristic emission spectra. These shifts are recorded by irradiating a point on the surface with a small laser and capturing the resulting nanotube emission with a short-wave infrared spectrometer. We found that consistency of film strain readings is significantly improved by thermal annealing of the deposited sensing layer before top coat application. Performance tests on a poly(methyl methacrylate) (PMMA) test specimen subjected to cyclic tensile stress show good strain sensing over the range from 0 to 2000 μϵ. Further tests on a stressed copper plate demonstrate that this method can be used with point-wise scanning to generate detailed two-dimensional maps of accumulated strain. To our knowledge, such maps cannot be obtained using any other nonperturbing strain-sensing method.

Creating fluorescent quantum defects in carbon nanotubes using hypochlorite and light

“…One of the most intriguing properties of semiconducting single-wall carbon nanotubes (SWCNTs) is their structure-specific fluorescence at short-wave infrared (SWIR) wavelengths 1,2 . This has inspired emerging applications in areas that include bioimaging 3–9 and optical noncontact sensing 10–12 . In addition, it has been shown that SWCNTs with some types of sparse covalent doping give spectrally shifted emission arising from the trapping of mobile excitons at the defect sites.…”

Synchro-Excited Free-Running Single Photon Counting: A Novel Method for Measuring Short-Wave Infrared Emission Kinetics

“…The spectral region from ca. 1000 to 1600 nm (often termed short-wave infrared or SWIR) is attractive for optical applications such as bioimaging, , telecommunications, and nondestructive inspection − because of favorable interactions with materials. For example, SWIR expands the detection window for optical imaging in biomedical research, offering improved image contrast through lower scattering and greatly reduced tissue autofluorescence …”

Beyond Color: The New Carbon Ink

“…For example, ink made from semiconducting SWCNTs dispersed by poly(9,9‐di‐ n ‐octylfluorenyl‐2,7‐diyl) in toluene was spray‐coated on a flexible substrate and then covered with a second flexible substrate. [ 145,146 ] This bilayer “skin” is then transferred to a substrate such as a wall. Local strain induced in this bilayer skin structure by the substrate causes spectral shifts in the nanotube PL.…”