Multilayer polypyrrole film

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. 

A number of derivates of pyrroles have been polymerized and manipulated into multilayer structures using the Langmiur-Blodgett technique [203]. This technique has been applied to manipulate electroactive conjugated polymers, mainly polypyrrole derivates, into multilayer thin films with well-defined layered structures and ordered molecular organizations [204]. In this way, amphiphilic polypyrroles and their precursors have been used, or soluble surface-active polypyrroles such as poly(3,4-dibutylpyrrole) [205] (Schemes 10.11 and 10.12). 

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... 

Monolayers of the surface active pyrrole derivatives 3-octadecyl pyrrole and 3-octadecanoyl pyrrole have also been successfully transferred into Y-type multilayer thin films. FTTR measurements have shown [23,24] that these materials both form highly ordered molecular organizations, each with its own specific type of molecular orientation. To illustrate these differences, the Fl lR reflection and transmission spectra of multilayer films of 3-octadecyl pyrrole (3-ODP) and 3-octadecanoyl pyrrole (3-ODOP) are displayed in Figure 12. Also included in this figi are the reflection and transmission spectra of a multilayer film of electrically conductive polypyrrole made with a 5000/1 mole ratio of pyrrole/3-octadecanoyl pyrrole using the proc ure described earlier. 

Figure 19. Dielectric constant and dielectric loss of a 50 layer polypyrrole/30DOP multilayer thin film as a function of frequency.

Fig. 122. Polymerization of pyrrole monomer in a preformed ferric stearate multilayer film (black dots represent electrically conducting polypyrrole) [764]...

Additional improvements can be achieved through the use of multilayers (based on different overlaid films). Such combination of the properties of different films has been documented with bilayers of Nation/CA (14) and Nafion/collagen (29). The former allows selective measurements of the neurotransmitter dopamine in the presence of the slightly larger epinephrine and the anionic ascorbic acid (Figure 5). In addition to bilayers, mixed (composite) films, such as PVP/CA (75) or polypyrrole/Eastman Kodak AQ (30) layers can offer additional permselectivity advantages, such composites exhibit properties superior to those of their individual components. Also promising are sensor arrays, based on electrodes coated with... 

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. 

Shirsat, M. D., Too, C. 0., and Wallace, G. G. (2008). Amperometric glucose biosensor on layer by layer assembled carbon nanotube and polypyrrole multilayer film, Eiectroanaiysis, 20, pp. 150-156. 

In all cases, the films were obtained by oxidative electropolymerization of the cited substituted complexes from organic or aqueous solutions. The mechanism of metalloporphyrin Him formation was suggested to be a radical-cation induced polymerization of the substituents on the periphery of the macrocycle. As it was reported for the case of polypyrrole-based materials ", cyclic voltammetry and UV-visible spectroscopy with optically transparent electrodes were extensively used to provide information on the polymeric films (electroactivity, photometric properties, chemical stability, conductivity, etc.). Based on the available data, it appears that the electrochemical polymerization of the substituted complexes leads to well-structured multilayer films. It also appears that the low conductivity of the formed films, combined with the cross-linking effects due to the steric hindrance induced by the macrocyclic Ugand, confers to these materials a certain number of limitations such as the limited continuous growth of the polymers due to the absence of electronic conductivity of the films. Indeed, the charge transport in many of these films acts only by electron-hopping process between porphyrin sites. 

From the fitting, this has a value of 36 pF (slightly greater than obtained with the uncoated electrode). Rppy represents the in-plane resistance of the polypyrrole-palmitic acid film, which from the curve fitting is found to be 3030 Q. The capacitance of the polypyrrole multilayer coated interdigitated electrodes measured in vacuum was only a few pF has been ignored in the model. 

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