ION PERMEATION AND EXCHANGE

Some of the first work studying the permeation properties of CP-based membranes was carried out by Burgmayer and Murray [1031]. They electropolymerized P(Py) onto a Au grid electrode held between two glass plates. They then investigated its ion permeation properties. As shown in Fig. 25-1. these differed for neutral (undoped) and cationic (doped) CP film. The response time of the film, measured chronoconductometrically (time vs. impedance on application of a potential pulse) was however poor, of the order of 4 min. 

Several studies from the Shimidzu group described a CP membrane which they ultimately utilized as an ion exchanger for deionization of water [1032-1034]. This comprised a P(Py) with a polymeric ( polyelectrolyte ) dopant, poly(vinyl sulfate) (PVS). This CP/dopant film used in the conventional manner, i.e. as an immobilized film on a solid metal substrate electrode. Although not strictly a membrane, we discuss this here because its ion exchange properties can also be used in similar systems fashioned into membrane form, and because nearly all the titles of the publications dealing with such CP ion exchange electrodes have, erroneously it may be contended, the word membrane in them. 

Huang et al. [937] described membranes constructed from P(ANi) and P(Py) deposited on substrates such as polypropylene and Teflon and using the CPs in their doped forms. These membranes were used to separate aqueous solutions, much like conventional proton exchange membranes. 

Stassen et al. [1026] described an interesting application for a supported CP membrane constructed by electrodepositing a 1 to 6 ixm thick film of poly(3-hexyl-thiophene) onto a thin (20 nm) Au layer deposited in turn on a Millipore Durapore membrane (average pore size 0.1 /im), i.e. the final configuration was CP/Au/-Durapore. They then mounted this membrane in a test cell and measured the permeability of the neurotransmitter dopamine (Dopa) through it as a function of potential applied to the membrane. They however found a poor variation of the permeation rate, only of the order of 40%. Response time for observable permeation was also poor, being of the order of hours. 

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