Poster
Presentation 05:
Chemoresistive Response of Carbon Nanotube-Polymer
Composites to VOCs
Samuel Anin, Catherine Ellen and Anthony
Guiseppi-Elie*
Department of Chemical Engineering
and Center for Bioelectronics Biosensors
and Biochips, Virginia Commonwealth
University, Richmond, Virginia 23284.
Carbon nanotube-polymer composites, at and around the
percolation threshold, are shown to be useful chemoresistive artificial
sensory receptors in an electronic nose. A toluene suspension of high performance
single-walled Carbon Nanotubes (CNT) was formulated by mixing with a host
polymer to varying concentrations. The polymer, a sulfonated Kraton®
(polystyrene-butadiene), was formulated at 10 different concentrations
that ranged from 90 wt. % CNT in 10% polymer to 10 wt. % CNT in 90 wt.
% polymer. Formulated composites were spun applied to glass cover slips
and onto microlithographically fabricated interdigitated microsensor electrode
(IME) devices. CNT-polymer formulations were characterized by AC–impedance
(both liquid and spun film), four-point conductivity, and optical microscopy.
The electrical impedance of each formula was determined over the range
of 10 mHz – 100 kHz using a model 1250 Frequency Response Analyzer from
Schlumberger. Four-point DC conductivity was measured using a Keithley
2010 Multimeter. Optical micrographs were obtained on a Licra at x350 magnification.
Finally, CNT- polymer-coated IME chips were tested for their response to
water vapor (30% RH), n-butanol (30% VP at RT) and methyl isoamyl ketone
(MIAK) (30% VP at RT) in a custom built Natural Olfactory Sensor Emulation
System (NOSES). NOSES simultaneously retrieves multiplexed data from
eight Volatile Organic Compound (VOC) sensors, a RH sensor and an RTD.
Composition dependence of the AC and DC conductivity places
the apparent percolation threshold of CNT-polymer at ca. 17 wt. % CNT.
This suggests that CNT aggregates behave as discrete particles (and not
as dispersed nanotubes) within this particular host polymer. Optical micrographs
support this view, as discrete domains of black CNT are visible even at
x350 magnification and down to 10 wt. % CNT. CNT- polymer chips were
shown to be responsive to RH, n-BuOH and MIAK and to have a maximum relative
resistance response (1-Rt/Ro) at compositions close to percolation threshold.
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