Cross-Linked Gold Nanoparticles
on Polyethylene: Resistive
Responses to Tensile Strain and Vapors
- Publication date
- Publisher
Abstract
In this study, coatings of cross-linked gold nanoparticles
(AuNPs)
on flexible polyethylene (PE) substrates were prepared via layer-by-layer
deposition and their application as strain gauges and chemiresistors
was investigated. Special emphasis was placed on characterizing the
influence of strain on the chemiresistive responses. The coatings
were deposited using amine stabilized AuNPs (4 and 9 nm diameter)
and 1,9-nonanedithiol (NDT) or pentaerythritol tetrakis(3-mercaptopropionate)
(PTM) as cross-linkers. To prepare films with homogeneous optical
appearance, it was necessary to treat the substrates with oxygen plasma
directly before film assembly. SEM images revealed film thicknesses
between ∼60 and ∼90 nm and a porous nanoscale morphology.
All films showed ohmic I-V characteristics with conductivities ranging
from 1 × 10<sup>–4</sup> to 1 × 10<sup>–2</sup> Ω<sup>–1</sup> cm<sup>–1</sup>, depending on
the structure of the linker and the nanoparticle size. When up to
3% strain was induced their resistance increased linearly and reversibly
(gauge factors: ∼20). A comparative SEM investigation indicated
that the stress induced formation and extension of nanocracks are
important components of the signal transduction mechanism. Further,
all films responded with a reversible increase in resistance when
dosed with toluene, 4-methyl-2-pentanone, 1-propanol or water vapor
(concentrations: 50–10 000 ppm). Films deposited onto high
density PE substrates showed much faster response-recovery dynamics
than films deposited onto low density PE. The chemical selectivity
of the coatings was controlled by the chemical nature of the cross-linkers,
with the highest sensitivities (∼1 × 10<sup>–5</sup> ppm<sup>–1</sup>) measured with analytes of matching solubility.
The response isotherms of all film/vapor pairs could be fitted using
a Langmuir–Henry model suggesting selective and bulk sorption.
Under tensile stress (1% strain) all chemiresistors showed a reversible
increase in their response amplitudes (∼30%), regardless of
the analytes’ permittivity. Taking into consideration the thermally
activated tunneling model for charge transport, this behavior was
assigned to stress induced formation of nanocracks, which enhance
the films’ ability to swell in lateral direction during analyte
sorption