Polypyrrole film coated

A molecularly imprinted polypyrrole film coating a quartz resonator of a QCM transducer was used for determination of sodium dodecyl sulphate (SDS) [147], Preparation of this film involved galvanostatic polymerization of pyrrole, in the presence of SDS, on the platinum-film-sputtered electrode of a quartz resonator. Typically, a 1-mA current was passed for 1 min through the solution, which was 0.1 mM in pyrrole, 1 mM in SDS and 0.1 M in the TRIS buffer (pH = 9.0). A carbon rod and the Pt-film electrode was used as the cathode and anode, respectively. The SDS template was then removed by rinsing the MlP-film coated Pt electrode with water. The chemosensor response was measured in a differential flow mode, at a flow rate of 1.2 mL min-1, with the TRIS buffer (pH = 9.0) as the reference solution. This response was affected by electropolymerization parameters, such as solution pH, electropolymerization time and monomer concentration. Apparently, electropolymerization of pyrrole at pH = 9.0 resulted in an MIP film featuring high sensitivity of 283.78 Hz per log(conc.) and a very wide linear concentration range of 10 pM to 0.1 mM SDS. 

An interesting composite material has been prepared by the electropolymerization of pyrrole on polyacetylene electrodes (45). Because oxidized polypyrrole is far more stable in air than polyacetylene, the resulting composite has the stability of polypyrrole. With different synthetic conditions, either a thin layer of polypyrrole was deposited over individual fibrils of the polyacetylene film or a dense polypyrrole film coated the entire film. When the dense polypyrrole film covered the entire polyacetylene film, the interior... 

Tezuka, Y, Kimura, T., Ishii, T., and Aoki, K., Concentration distribution of conducting species with time-resolution in electrochemical undoping process at the polypyrrole film coated electrode in the light of electric percolation, J. Electroanal. Chem., 395, 51-55 (1995). 

Polymerization solutions were 0.5 M in pyrrole and 0.2 M in Et4NBF4. Pyrrole was polymerized (and deposited) galvanostatically a current density of 1.0 mA cm" was employed. Reproducible steady state potentials of 0.84 V + 0.01 V were observed during film deposition at this current density. After deposition, the polypyrrole film-coated electrode was transferred to monomer-free, 0.2 M Et4NBF4. All subsequent electrochemical measurements were performed in this electrolyte. 

Typical Nernst plot for polypyrrole film-coated electrode obtained from coulometric titration experiment. Film thickness - 0.27 fm. See text. 

Fig. 37.18 Critical currents obtained at various temperatures for a single 2 fim polypyrrole film coated onto a 100 /jLtn wide x 3 mm long microbridge formed from a 500 A thick YBa2Cuj07- film. Data are shown for (A) neutral and (B) doped polypyrrole cases. (Adapted from Ref. 11.)...

The polymerization conditions used to prepare polypyrrole not only determine the polymer composition, but also influence the structure of the polymer from the molecular level to the microscopic level. In this section, the studies characterizing the detailed structure of polypyrrole films, coatings, particles and colloidal dispersions are reviewed. These studies provide the foundation for understanding the properties of polypyrroles, as described in Chapter 3. 

Figure 4. Time course of HeLa cell diameter change using a polypyrrole film-coated and a bare Pt microelectrode under a rectangular wave potential at 5 Hz,... 

Polypyrrole film-coated electrode at +0.4 V to -0.6 V peak to peak potential. 

Amplification of Electrochemical Effect Using Polypyrrole Film-Coated Microelecrode... 

When a rectangular potential waveform from -0.6 V to 0.4 V at a frequency of 5 Hz was employed using a polypyrrole film-coated microelectrode prepared by following the conditions described above, the target HeLa cell swelling and burst were induced within 20 s. In the latter potential range polypyrrole is reported to be stable. Figure 4 shows that... 

Figure 5. Selective electrochemical cell swelling and burst under +0.4 V to -0.6 V peak to peak rectangular wave potential at 500 Hz using a polypyrrole film-coated microelectrode. 

Figure 5 shows the selective effect when a rectangular wave potential from -0.6 V and 0.4 V at 500 Hz was employed. Under these conditions, the target HeLa cell on the surface of a polypyrrole film-coated microelectrode swelled and burst after 33 s. A non-target cell directly in contact with the target cell and at a position of 16 pm from the microelectrode showed no morphological changes for 10 min. 

Employment of a polypyrrole-coated microelectrode brought about the amplification of the electrochemical effect. By the adoption of a high frequency square wave potential application, the susceptibility of the target cell at the interface of the microelectrode to bursting was remarkably enhanced. It should be noted that the polypyrrole film-coated electrode demonstrated interesting functions even under the conditions needed for a bare platinum electrode. This might be interpreted by the electrochemically induced influx of dopant anions onto the polypyrrole film matrix, which seems to result in drastic pH changes in the localized area, i.e., the interface between an electrode and bulk solution. 

Figure 4.42. Plot of imaginary impedance versus 1/tufor PPY-PSS film coated on Pt [12]. (Reprinted from Journal of Electroanalytical Chemistry, 420, Ren X, Pickup PG. An impedance study of electron transport and electron transfer in composite polypyrrole plus polystyrenesulphonate films, 251-7, 1997 with permission from Elsevier and from the authors.)...

The presence of a derivatized surface layer can affect the energetics as well as the kinetics of electrode reactions. It has been found that the flatband potentials of -Si and p-Si electrodes coated with conducting polypyrrole films are shifted by 300 and 500 mV in CH3CN solution." The reaction kinetics on polymer derivatized surface can further be enhanced by impregnation of noble metals such as Pt particles into the... 

These conducting polymers are sometimes termed organic metals, and their formation as thin-film coatings on an electrode involves nucleation phenomena so perhaps by analogy with metal electrodeposition under ultrasound there have been studies to improve the quality of the deposited materials. Polypyrrole readily forms acceptable films under a wide variety of conditions [174], although there are subtle distinctions in behavior as a result of exact preparation procedure [175], Ultrasound from 38 or 500 kHz baths does not appear to appreciably improve polypyrrole film formation, at least from MeCN electrolyte at the normal current density of 1 mAmp... 

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