Polypyrrole LB Film

Propagation of the polymerization is seen by a change in color of the LB film from the semitransparent white of the precursor LB film to the blackish green or reddish brown of the conductive film. Several other methods were demonstrated to obtain conductive polypyrrole LB films [86,87]. The conductive LB films of polyaniline [85,87] and poly thiophene [85,88—93] were also reported. For the latter LB films, a maximum conductivity of 5 S/cm was obtained by NOPF6 doping [91]. 

Figure 9 Electrochemical polymerization of polypyrrole LB film. (From Ref. 84.)...

This study describes initial electrochemical experiments, aimed at the development of an amperometric glucose biosensor using ferrocene as the electron mediator, incorporated into an oriented polypyrrole LB film. A variety of monolayer samples were prepared for cyclic voltammetry (CV) studies to determine if the ferrocene was detectable electrochemically in such a configuration. This was an important criterion,as... 

In the field of molecular electronics the preparation of LB films is of primary importance. Thiophene oligomers [326], poly(alkylthiophene)s [327], and polypyrroles [328,329] have been used for this purpose. 

Recent developments in the field of molecular electronics have been oriented toward the synthesis of model molecules as molecular wires [387] or molecular rectifiers [388] or to the preparation of LB films [388]. LB films containing thiophene oligomers [389,390], polyalkylthiophenes [391] or polypyrroles [392-6] have been prepared. 

Just after the first conductive LB film based on molecular conductors was reported, the studies extended to those based on conductive polymers. Heterocyclic polymers, i.e. polypyrroles and polythiophenes are mainly used as film-forming materials due to their stability compared with aliphatic conductive polymers like polyacetylenes. The other stable polymers, for example, polyanilines, poly(p-phenylenevi-nylene)s, etc. are also the subjects of LB studies. A... 

Figure 14.36. The solid state reactions of iron(III) stearate LB films with HCl gas and pyrrole vapour to form a conductive polypyrrole. Coimected black dots symbolise polypyrrole. (Reproduced by permission of The Royal Society of Chemistry from ref. 259.)...

Detailed studies of the level and type of molecular orientation present in LB films of conducting polymers and their precursor monomer assemblies have been carried out for both polypyrrole and polythiophene based systems [23-27]. The results obtained from tiiese studies are summarized below. 

ORIENTATION STUDIES OF LB FILMS FABRICATED WITH SURFACE ACTIVE PYRROLES AND POLYPYRROLE. The molecular organizations of multilayer thin films of the surface active pyrrole derivatives used to formed mixed monolayers with electrically conductive polypyrrole chains and ferrocene derivatized pyrroles have also been examined by FTIR reflection/absorption techniques. The materials investigated in... 

An analysis of the vibrational bands associated with the electrically conducting polypyrrole chains (spectral region not shown) has further demonstrated that the polymer chains are preferentially oriented with the long axis of their fully extended backtones contained within the plane of the substrate. All of these observations are consistent with a structure in which the polypyrrole chains are sandwiched between oriented bUayers of the surface active pyrrole. X-ray diffraction analysis, however, also shows that a small portion of the multilayer film is comprised of separate molecul stacks of 3-octadecanoyl pyrrole molecules packed with their normal bilayer repeat distance. This suggests that some of the surface active pyrrole molecules under a reorganization during film transfo to form isolated molecular domains. Nevertheless, the primary stracture of Ae electrically conductive LB films is comprised of polypyrrole chains isolated between layers of the surface active pyrrole molecules. 

Rubner and associates [19,30] have shown that electrically conducting LB films fabricated from polypyrrole/30DOP monolayers exhibit unusually large dielectric constants over a wide frequency range. The large dielectric constants are believed to be... 

The LB technique may also be combined with solid-state chemistry methods to produce novel molecular architectures. For example, a network of conductive polypyrrole (molecular wires ) may be obtained in a fatty acid matrix [37, 38]. First, monolayers of the iron salt of a long-chain fatty acid (e.g., ferric pahnitate) are assembled on an appropriate substrate. The multilayer film is then exposed to saturated HCl vapor at room temperature for several minutes. During this process, a chemical reaction transforms the fatty acid salt into layers of ferric chloride separated by layers of fatty acid. In the third and final step, the film is exposed to pyrrole vapor and a reaction occurs between the pyrrole and the ferric chloride, producing polypyrrole distributed within the multilayer assembly. 

Here, we describe the construction and evaluation of a conductimetric pH sensor, based on a multilayer polypyrrole film [8]. The sensor is an interdigitated electrode array coated with the polymer by using the Langmuir-Blodgett (LB) technique [9]. Impedance spectroscopy has been used to investigate the complex admittance of the device when exposed to aqueous solutions of different pH. 

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