Polythiophene films, electrochemical

Table 14.11. / and p values (%) for polythiophene films electrochemically prepared from silylated monomers... 

Polythiophene films can be electrochemically cycled from the neutral to the conducting state with coulombic efficiencies in excess of 95% [443], with little evidence of decomposition of the material up to + 1.4 V vs. SCE in acetonitrile [37, 54, 56, 396,400] (the 3-methyl derivative being particularly stable [396]), but unlike polypyrrole, polythiophene can be both p- and n-doped, although the n-doped material has a lower maximum conductivity [444], Cyclic voltammetry shows two sets of peaks corresponding to the p- and n-doping reactions, with E° values at approximately + 1.1 V and — 1.4 V respectively (vs. an Ag+/Ag reference electrode)... 

Tourillon 136,398) has reported that polythiophene films formed electrochemically are smooth up to 200 nm thick, after which they become rough and eventually powdery, at thicknesses above a few pm. The films have a density of about 1.5 g cm-3. Undoped films of polymethylthiophene show fibrils of 25 nm diameter which swell to 80 nm on doping to 25 mol % with perchlorate conter-ions. 

As summarized in Table 8.3, both the electrochemical capacity and electroconductivity are markedly increased when the polypyrrole and polythiophene films are prepared in the ionic liquid. This may be attributable to the extremely high concentration of anions as the dopants, which results in a much higher doping level. 

Burgmayer P and Murray R W 1984 Ion Gate Electrodes. Polypyrrole as a switchable ion conductor membrane J. Phys. Chem. 88 2515-21 Otero T F and de Larreta E 1988 Conductivity and capacity of polythiophene films impedance study J. Electroanal. Chem. 244 311-18 Sunde S, Hagen G and Odegird R 1993 Impedance analysis of the electrochemical doping of poly(3-methyl-thiophene) from aqueous nitrate solutions J. Electroanal. Chem. 345 59-82 Zaborsky O R 1973 Immobilized Enzymes (Cleveland, OH Chemical Rubber Company) (see especially pp 69,87)... 

Unsubstituted polythiophene (PT) is an intractable material because it is neither soluble nor fusible, although films electrochemically prepared under certain conditions may be stretch-deformed. Generally speaking PT prepared by purely chemical routes turns out to be more crystalline than their electrochemical counterparts, as will be discussed in the following. 

Electrochemical deposition of polythiophene films from solution of mono- or bithiophenes is one of the commonly used methods and can also be applied to prepare oligothiophene films. The films are formed in situ during the polymerization process. Due to the oxidative polymerization only doped (oxidized) materials are obtained and appropriate counter-ions have to be added. This method can only be applied to conductive substrates. 

R. J.Waltman, J.Bargon and A.F.Diaz, Electrochemical studies of some polythiophene films, J. 

Figure 11.21 Mott-Schottky plot for polythiophene. Electrolyte 0.1 mol-dm LiBF4/H20, potentials versus saturated calomel electrode (SCE). The polythiophene films were prepared by electrochemical oxidation in acetonitrile.

Tehrani, R, N.D. Robinson, T. Kugler, T. Remonen, L.-O. Hennerdal, J. Hall, A. Malmstrom, L. Leenders, and M. Berggren. 2005. Patterning polythiophene films using electrochemical overoxidation. Smart Mater Struct 14 N21-N25. 

Elarima, Y, Y. Kunugi, K. Yamashita, and M. Shiotani. 2000. Determination of mobilities of charge carriers in electrochemically anion-doped polythiophene film. Chem Phys Lett 317 310. 

Shi and co-workers prepared polythiophene films with different roughnesses by electrochemical polymerization of thiophene in boron trifluoride-diethyl etherate (BFEE) [42]. The highest WCA of 116° on polythiophene film was observed. To further increase the WCA, aligned polythiophene nano-tubes were synthesized using anodized aluminium oxide (AAO) as template. The WCA increased to 134° (Fig. 7). As a comparison, the WCA of polythiophene polymerized in acetonitrile solution was measured to be less than 75°. 

R. J. Waltman, J. Bargon, A. F. Diaz, Electrochemical studies of some conducting polythiophene films, J. Phys. Chem., 87, 1459-1463 (1983). 

V versus 1.65 V for thiophene) may be substituted for thiophene and copolymerized with pyrrole. A mixture of approximately 90% pyrrole and 10% terthiophene in an electrolyte of 0.1 M tetraethylammonium perchlorate in acetonitrile produced pyrrole-like films. A redox potential in between that of the homopolymers was observed. The conductivity (1 S cm" ) of the film has a value that lies between typical values for polypyrrole (o- = 10 -10 S cm" ) and polythiophene produced electrochemically from terthiophene (o- = 10" -10" S cm" ). Furthermore, x-ray photoelectron spectra showed the presence of sulfur and nitrogen and indicated a stoichiometry of six pyrroles per thiophene unit. 

V(bithiophene) 1.14 (26) [46]. Electrochemical polymerization of (25) and (26) was possible under conditions close to those for thiophene and (25) and (26) was possible under conditions close to those for thiophene and bithiophene, respectively. Trimethylsilyl groups permitted specific activation of the 2 and 5 positions with respect to the electrochemical oxidation and allowed the preparation of polythiophene films, starting from oligomers, which gave rise to low selectivity without silyl substituents, or monomers with electron-withdrawing substituents. Masuda et al. elec-trochemically polymerized (25), (27) and (28) [47]. Elemental analysis of the resulting films indicated that almost all silicon atoms were eliminated during polymerization. IR spectra, absorption spectra and cyclic voltammometry indicated that the films were made up from polythiophene. Roncali et al. electro-chemically oxidized (29) and obtained a polythiophene film [48]. This particular structure of (29) allows electrochemical preparation to be performed at a very low substrate concentration while the reduction of the silicon to monomer ratio to its minimum value would lead to further improvements in the quality of the polythiophene film. 

Polythiophene films prepared electrochemically were stretched to stretching ratio of 1.5 and annealed at 100°C for 1 hour [68]. The stretching increased the... 

According to the Raman and photoluminescence criteria (see above), polythiophene films prepared by electrochemical oxidation of a-silylated mono-, bi- and terthiophene monomers (polymers called pTh-El, pTh-E2 and pTh-E3, respectively. Table 14.10 and Scheme 14.32) have been analysed [10]. 

Figure 14.19. Photoluminescence bands of electrochemically prepared polythiophene films (a) pTh-E2, (b) pTh-E3, (c) pTh-El, 2 = 5145 A (Reprinted with permission from ref. 10).

Tehrani P, Robinson ND, Kugler T, Remonen T, Hennerdal LO, HaU J, Mahnstrom A, Leenders L, Berggren M (2005) Patterning polythiophene films using electrochemical over-oxidation. Smart Mater Stmet 14 N21-N25... 

Kaneto K, Kohno Y, Yoshino K, Inuishi Y (1983) Electrochemical preparation of a metallic polythiophene film. J Chem Soc Chem Commun 1983(7) 382-383... 

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