Broadband Dielectric Spectrometer

PEDOT-PSS/poly(iV-vinylp3nTolidone) (PVP) and PVP nanofibers were independently prepared by electrospinning. The color of as-spun PEDOT-PSS/PVP nanofrbers was light blue, indicating the incorporation of PEDOT-PSS in the nanofibers, whereas that of as-spun PVP nanofibers was white. The incorporation of PEDOT-PSS was confirmed from FT-Raman spectra. 

The distribution of diameters of PEDOT-PSS/PVP nanofibers was insignificantly effected by the applied voltage. To compare PEDOT-PSS/PVP nanofibers with PVP nanofibers, electrospinning was performed under different conditions except the distance was constant between the tip and the collector (15 cm). PEDOT-PSS/PVP nanofib-ers were obtained while applyinga voltage of 11 and 18 kV and a flow rate of 0.2 mL/h and the average diameters were found to be 153 and 212 nm, respectively. By incorporating PEDOT-PSS in PVP, the electrical conductivity of composite nanofibers was improved. 

7 Organic Vapor-Sensing Characteristics of PEDOT-PSS/PVP and PVP Nanofibers 

The sensing behaviors of PEDOT-PSS/PVP (Fig. 5.21) and PVP nanofibers on ethanol, methanol, THF, and acetone vapors are studied. The sensing was carried out for several q cles by repeated exposure of the nanofibers to saturated organic vapors and air alternately. Both PEDOT-PSS/PVP and PVP electrospun nanofiber sensors have exhibited good reversibility, reproducibility and response and recovery time. The response and recovery time of PEDOT-PSS/PVP nanofibers upon exposure to ethanol vapor are much faster than those of PVP nanofibers. 

By exposing PEDOT-PSS/PVP and PVP nanofibers to the solvents, these solvents produced opposite electrical responses in the PEDOT-PSS/PVP and PVP nanofibers. In the case of alcohol vapor sensing, the resistances of PEDOT-PSS/PVP and PVP nanofibers decreased and became constant upon certain saturation, but resistance was increased during alcohol vapor desorption by air. Such decrease may be associated with the dielectric constant of alcohols (Table 1.5]. 

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One of the fluids was pure Mazola corn oil and the other was the same oil colored with oil-based Teal dye and doped with oil-miscible antistatic Stadis 450 to increase the conductivity and permittivity [91]. The latter values were measured with a broadband dielectric spectrometer in a spatially uniform low electric field for frequencies of 0.5-1 kHz. 

Conductivity measurements were realized using broadband dielectric spectrometer. Nanofiber mat samples were prepared with the area of 4 cm for measurement As a result, conductivity values increased with an increase of PEDOT-PSS content at high frequency. Figure 5.19 shows the conductivity changes with the increase of the CP in the nanofiber composite. 

Dielectric relaxation spectra were collected isothermally using a Novocontrol GmBh Concept 40 broadband dielectric spectrometer in the frequency range 0.1-10 Hz. Temperatures were controlled within 0.2°C. The diameter of the top electrode was 15 mm while the diameter of the bottom electrode was 30 mm. In order to better resolve the spectra due to high values for dielectric loss caused by high conduction loss, the dielectric loss was calculated using the expression (1) (Wubbenhorst and Tumhout, 2002). 

Sample Preparation and Dielectric Spectroscopy Measurements. Dielectric relaxation spectra were collected using a Novocontrol GmbH Concept 40 broadband dielectric spectrometer over the frequency range 0.01 Hz - 3 MHz and over the temperature range of 0 to 100° C. The temperature stability of the instrument was controlled to within 0.2° C. 

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