Estimation of charge trapping in bilayers of coducting polymers composed of polypyrrole and poly(N‐methylpyrrole)

Abstract

Charge trapping effects were studied in bilayers of conducting polymers composed of poly(N-methylpyrrole) (PMPy) and polypyrrole (PPy), by comparing redox charges of the polymer [Q(ox/red)] obtained by integration of cyclic voltammetric and chronoamperometric curves for single films and bilayers with variable thickness of both components. Charge trapping factors, TF, for PMPy(inner layer)/ PPy(outer layer) bilayers were determined using the definition: TF = 1 -Q(ox/red)~~~/Q(ox/red)ppr. where Q(ox/red)F& is redox charge of PPy in the bilayer, Q(ox/red)pp, relates to the charge for a single PPy film of the same thickness as that in the bilayer. Since the formal potential of PMPy is higher than that of PPy, the outer PPy film cannot be entirely reduced due to low conductivity of PMPy at negative potentials. The estimated charge trapping factor is independent of the outer layer thickness, it depends, however on the thickness of the inner film. For the reverse sequence of polymers, PPy/PMPy, charge trapping was not observed. Modification of the outer PPy layer by immobilized poly(4-styrenesulfonate) anions changes the response of the bilayer due to low permeability of the cation-exchanging outer polymer to anions. Therefore perchlorate anions compensating charge of PMPy film were found to be entrapped in the polymer matrix under conditions of cyclic voltammetry.

Responsive Organometallic Polymer Grafts: Electrochemical Switching of Surface Properties and Current Mediation Behavior

“…12 Although redox signals have been to some extent utilized to trigger responsive behavior, corresponding studies are still rather sparse in the macromolecular literature. Redox responsive systems however offer great advantages as compared to the hitherto investigated stimulus responsive grafts, as they represent an effective and fast way to control the interfacial properties such as surface charge density, 13 ion or molecule permeability, 14 electronic properties, 15 hydration, 16 and adhesion. 17 Electrochemical signals can also be used to address structures with sizes down to the length scales of 20 nm; thus, redox responsive systems would be "nanotechnology compatible" due to this nanoscale addressability.…”

Charge transfer processes in bilayers and co-polymers composed of C60Pd and 2′-ferrocenylpyrrolidino-[3′,4′;1,2]C60Pd two-component polymers

“…Polymers have also been used for construction of bilayers. Both redox polymers [25][26][27][28][29][30][31][32][33] and conjugated conductive polymers [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] have been used as components of bilayer and multilayer electrodes. In the case of bilayers constructed from redox polymers, the oxidation or reduction of the outer film is mediated by the inner layer.…”

The electrochemical formation and properties of bilayers composed of polypyrrole and C60Pd films

“…19,20 Recently, the preparation and properties of a variety of bilayers composed of redox polymers have been studied. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] Charge and mass transport are very complex in such systems. The electrochemical behavior of these bilayers depends on the relative energy level position of the inner and outer layers 27,29,33 and on the permeability of the outer layer toward ions present in the solution.…”

“…For example, the outer layer of the bilayers of the type poly(2,2'-bithiophene)/polypyrole or polypyrrole/poly(N-methylpyrrole) could be kept in the oxidized state for a longer time than as a separate layer. [27][28][29]34 On the other hand, the ion-exchanging properties of the outer layer determine the possibility of the inner layer oxidation or reduction.…”