Capacitance, poly films

Figure 5. Cyclic voltammograms of (a) 2,5"" -di-methyl-a-hexathiophene and (b) poly(2,2 -bithio-phene) films in acetonitrile containing 0.1 M E NCIO 103 (Reprinted from G. Zotti, G. Schia-von, A. Berlin, and G. Pagani, Electrochemistry of end-ca )ed oligothienyls-new insights into the polymerization mechanism and the charge storage, conduction and capacitive properties of polythiophene, Synth. Met. 61 (1-2) 81-87, 1993, with kind permission from Elsevier Science S.A.)...

Au-gate poly-Si thin film transistor Au-gate MIS capacitance 18-mer ssDNA, 1012 - 1013 ssDNA/cm2 5 mM phosphate buffer pH 7.2 18-mer cDNA A Eh 355 mV AVfi, 140mV 1 h 30 min Ag/AgCl [36]... 

High-frequency welding probably is the technique used most widely for joining both rigid and flexible poly(vinyl chloride) film and sheet. (It has been called also radio-frequency or capacitance heating welding.)... 

Common polymers such as polystyrene (PS) and polymethylmethacrylate (PMMA) have been used as gate dielectric materials [7,20,46]. Their ready availability made them some of the early polymers investigated by researchers in the field [11,39,47]. However, the low capacitances of these films made them less attractive than other polymers. Poly(4-methylstyrene) has been explored as a possible polarizable gate insulator [48]. 

Hashmi and Upadhyaya compared the electrochemical properties of the electrochemically synthesized MnO /PPy composite electrodes, fabricated with different electrolytes, namely polymer electrolyte film (polyvinyl alcohol [PVA]-HjPO aqueous blend), aprotic liquid electrolyte (LiClO -propylene carbonate [PC]), and polymeric gel electrolyte (poly methyl methacrylate [PMMA]-ethylene carbonate [EC]-PC-NaClO ) [60]. The cell with aqueous PVA-H PO showed non-capacitive behavior owing to some reversible chemical reaction of MnO with water, while the MnO / PPy composite was found to be a suitable electrode material for redox supercapacitors with aprotic (non-aqueous) electrolytes. The solid-state supercapacitor based on the MnO /PPy composite electrodes with gel... 

In summary, two processes should be considered as indicated above when the polymer is reduced and can be represented by the equivalent circuit of Figure 3a. In this diagram, represents the solution resistance, Q refers to the double layer capacitance, Ri is the intrinsic resistance due to charge transfer of the redox process within the polymer film, W is the equivalent to the ionic diffiision at the film/electrolyte interphase, Q is the film capacitance, and Rf is the film resistance. In all cases, an electronic resistance component of the polymer film is considered to be connected in series with the solution resistance. Similar equivalent circuits were described in the literature for poly(2,5-di-(-2-thi yl)-thiophene) films earlier in the literature (25). The value of e electrical r istance of the polymer film varies considerably according to the applied potential to the polymer film, the film thickness and the electrol3rtic medium in which the measurement is taking place (26). Polymer film parameters are summarized in Table 1 for both oxidized and reduced states, respectively. 

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