Conducting polymers constant-potential method

Conductive polymer films based on polypyrrole and hyaluronic acid were synthesized using both a galvanostatic method—by applying current at a constant intensity ranging between 0.5 and 10 mA for periods varying between 60 and 150 minutes—and a potentiostatic method with the constant potentials ranging between 0.3 and 0.75 V... 

PPy nanotube can be synthesized by applying current of 2-3 mA for 1 min. When the time is increased to 15-40 min, PPy nanowires will be produced. Conducting polymer nanotube and nanowires prepared by this electrochemical method using AAO templates can be applied in field emitting applications [185,186]. Figure 1.16 shows a uniform layer of polyaniline nanowires produced at constant potential at 1.0 V for 10 min through the AAO template [187]. 

This phenomenon has been studied by different combined electrochemical techniques such as -> spectroelec-trochemistry, radioactive -> tracer method, -> electrochemical quartz crystal microbalance, conductivity etc. by varying the experimental parameters, e.g., film thickness, the composition and concentration of the electrolyte solutions, the wait-time at different waiting potentials, and temperature [iii-x]. Several interpretations have been developed beside the ESCR model. The linear dependence of the anodic peak potential on the logarithm of the time of cathodic electrolysis (wait-time) -when the polymer in its reduced state is an insulator -has been interpreted by using the concept of electric percolation [ix]. Other effects have also been taken into account such as incomplete reduction [vii], slow sorp-tion/desorption of ions and solvent molecules [iii-vi], variation of the equilibrium constants of -+polarons and - bipolarons [viii], dimerization [xi], heterogeneous effects [xii], etc. 

The method of choice for the measurement of resistance when one wishes to avoid potential drops across the contacts is the four-probe method. In this method, four low-resistance contacts are made diagonally (in the shape of a diamond) on the polymer surface using thin wires fixed to the surface by preparations such as silver epoxy (soft cure) or Electrodag. A constant current is passed through two contacts and the potential difference is measured across the other two. From this the resistance or conductivity may be calculated. The condition to be satisfied in this measurement is that the thickness of the polymer film (or pellet) should be much less than the length. 

An SECM feedback response to an electroactive polymer film can be controlled either by ET kinetics at the film-solution interface or by film conductivity. The contribution of lateral film conductivity to the effective ET rate measured by SECM was addressed in the recent study of polyaryl multilayers attached with ferrocenes [65] or ferrocene-terminated dendrimers [69] on unbiased carbon electrodes. In the latter study, the dependence of apparent ET rate constant, feei. on the generation of dendrimers (Table 6.2) was ascribed to the different efficiencies of electron transport inside and between dendrimers (Figure 6.22). Interestingly, the theory of the aforementioned triple potential step method predicts its potential to separately determine heterogeneous ET rate and lateral conductivity for a thin polymer film coated on an insulating surface [70]. 

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