(Invited) Progress Towards a Novel Technology for Non-Contact Strain Measurements Based on SWCNT Fluorescence Spectroscopy

One of the most distinctive properties of semiconducting single-walled carbon nanotubes (SWCNT) is their emission of structure-specific fluorescence (band gap photoluminescence) in the short-wave infrared (SWIR) spectral region. The fluorescence peak from each (n,m) structural species shifts in wavelength as the nanotube’s band gap is altered by axial strain. These shifts are known from theory and experiment to depend on the nanotube’s chiral angle and on its mod (n‑m,3) value, and they are linear with strain for realistic axial deformations. We have previously shown that this effect may lead to a new strain measurement technology (called S⁴, for strain-sensing smart skin) in which individualized SWCNTs embedded in a polymeric film serve as strain sensors and readout is achieved by non-contact optical methods.¹ Recent research progress aimed at enabling such an implementation will be described. Focus areas include processing and dispersing SWCNTs for effective use in S⁴; comparing suitability of different polymer formulations as S⁴ hosts; applying and stabilizing the S⁴ films; understanding factors that influence interfacial adhesion between SWCNTs and host molecules; miniaturizing the optical hardware to allow excitation and capture of SWCNT fluorescence spectra with hand-held devices; refinement of data analysis methods for deducing strains from spectral data; tests of sensitivity and reproducibility for S⁴ measurements with plastic, aluminum, and steel substrates; and construction of two-dimensional strain maps from sets of single-point measurements.

¹ P. A. Withey, V. S. M. Vemuru, S. M. Bachilo, S. Nagarajaiah, and R. B. Weisman, Nano Lett. 12, 3497 (2012).