Conducting polymers film formation

The first subdiscipline of chemistry in which the QCM was widely applied was electrochemistry. In 1992 Buttry and Ward published a review entitled Measurement of interfacial processes at electrode surfaces with the electrochemical quartz crystal microbalance , with 133 references [8]. This is the most widely cited paper on quartz crystal microbalances. After presenting the basic principles of AT-cut quartz resonators, the authors discuss the experimental aspects and relation of electrochemical parameters to QCM frequency changes. In their review of the investigation of thin films, they discuss electrodeposition of metals, dissolution of metal films, electrovalency measurements of anion adsorption, hydrogen absorption in metal films, bubble formation, and self-assembled monolayers. The review concludes with a brief section on redox and conducting polymer films. 

The most popular ways to immobilise enzymes on conducting polymers are either to entrap the enzyme within the growing polymeric films [56, 59, 153, 154] or to use a two-step procedure based on the formation of a functionalised conducting polymer film followed by the covalent binding of the enzyme at the functional groups at the polymer surface [125, 155, 156]. 

Piezoelectric microgravimetry in conjimction with electrochemical measurements is a very powerful but relatively simple and cheap techrrique, and so within the last twenty years it has become one of the most popular hyphenated techrriques for studying the formation of conducting polymer films and ion and solvent exchange processes that occur during their redox reactions, which provide valtrable information about the reaction mechanism [6-9,43,70,89,90,98,107,151,153,154,156-166,168-232],... 

Formation of ultrathin non-conducting polymer films has also been reported by Hammond et al. using ionic attraction on the surface of the carboxylate terminated SAM allowing layer-by-layer deposition of ionic multilayers [33,34,139-141]. These systems have been combined with patterning techniques and have been examined with respect to their optically responsive properties. Viologen-based polyelectrolytes have also been shown to adsorb onto a carboxylate SAM surface, forming an electroactive thin film [146]. 

UVERS study of the formation of electron conducting polymer films at a gold electrode, and of their modification by intercalation of metal aggregates or of iron phthalocyanine ... 

The role of the dopant potential on the stability and magnetic and optical properties of polarons and bipolarons in conducting polymers is shown with the aid of calculations of singlet and triplet states of a bipolaron [167] and by spectroelectrochemical and conductivity measurements [168-170]. The X-band optically detected magnetic resonance of PHT and PDDT shows that the distant intrachain polaron recombination is temperature-independent and identical in films and solutions. However, the triplet polaronic excitation decay is observable in films, but not in solutions [171], Electrochemical in situ conductivity and EPR measurements of PT films were performed in several solutions [172]. The results indicate that polarons merely seem to initiate the electrical conductivity. The electronic delocalization of polarons is restricted to a relatively short chain length at low potentials. As the polaron concentration increases (spin density maximum), bipolarons are generated immediately (probably too fast for the detection of polarons by EPR). Thus the bipolarons prevail in the fully conducting polymer films and as a consequence should be mainly responsible of the intrinsic conductivity [172]. Asymmetrically disub-stituted PBT display well-defined redox processes which are correlated to the consecutive formation of radical cations, dimerized radical cations, and dications [173]. 

The solubility of POT not only facilitates its processing, but allows the polymer to be doped in solution as an alternative method to the formation of a solid conducting material [239]. As the result of the electrochemical doping of PATs in solution, the doped conducting polymer film is deposited on the anode surface [240]. 

Figure 8.8. (a) Formation of a sample-spanning bond-percolation cluster on a square lathee at the percolation threshold (p = 0.6). (b) Cluster of conductive zones in a conductor-insulator mixture formed above the percolation threshold [46, 155]. (Image (a) reprinted with permission from Stauffer D, Aharony A. Introduction to percolation theory, London Taylor Francis, 1994 (b) reproduced from Chem Phys Lett, 375(5-6), Malek K. Dynamic Monte-Carlo simulation of electrochemical switching of a conducting polymer film, 235-44, 2002, with permission from Elsevier.)... 

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