Biomedical Engineering Reference
In-Depth Information
Figure 9.22
(
) TEM images of pristine (AG-SWCNTs) and purified
(OX-SWCNTs; OA-SWCNTs) HiPco SWCNTs used as filler in
the LB composite. (
Top
) SEM images of LB film based on a
10-monolayer 75 wt.% nanocomposite of pristine and
purified SWCNTs in CdA host-matrix. This figure is reprinted
and adapted with permission from IOP [186].
Down
Figure 9.23 shows the typical transient time responses of three
SAW 433 MHz devices coated with SWCNTs-in-CdA 75 wt.% two-
monolayer thick LB nanocomposite film with three various types
of SWCNTs filler — raw (AG-SWCNT) material and two differently
purified (OX-SWCNT and OA-SWCNT) materials, toward three
5 min pulses of methanol at decreasing concentrations, at room
temperature. The increase in mass of the vapor molecules adsorbed
by a single coating causes a downshift in the frequency of the SAW
oscillator. The variation in the magnitude of the frequency response
of the three SAW sensors depends on the different electrical and
structural properties of the gas-sensitive coating modified by the
purification process. In fact, adsorbed gas molecules alter the
conductivity of the LB coating leading to a modification in the velocity
of the SAW, which in turn leads to a change in the resonant frequency
of the SAW oscillator sensor. Hence, the surface conductivity of the
LB coating, modified by the different purification steps of the filler
in the nanocomposite, strongly affects the SAW frequency response
via acoustoelectric effect and determines a different acoustic gas
response depending on the purification of the carbon nanotube
fillers in the LB nanocomposite. Therefore, the mass loading
produces common downshift of the frequency response, while the
