Electrochemistry of Conductive Polymers. XXVI. Effects of Electrolytes and Growth Methods on Polyaniline Morphology

Abstract

Effects of counterions and growth methods on polyaniline growth have been studied using the electrochemical quartz crystal microbalance and other related techniques. The results indicate that the polymer growth rates and the morphology of polymer surfaces are very different depending on the electrolytes and growth methods used. During the first cycle of the potentiodynamic growth, the weight increase is observed with a low coulombic efficiency. However, the number of electrons required for the deposition of one aniline unit quickly approaches 2.0 beginning from the second cycle, and the current efficiency becomes higher as the number of cycles increases. As the film grows, the anion insertion and deinsertion become increasingly important. For a thick polymer film in the H 2 SO 4 solution, the doping/dedoping process is not reversible, although it is reversible in HClO 4 solutions. During the potentiostatic and galvanostatic polymerization, relatively low charge efficiencies were observed due to the degradation reactions. These results were consistent with the scanning electron microscope images.

The effect of anion identity on the viscoelastic properties of polyaniline films during electrochemical film deposition and redox cycling

“…However, we wished to determine materials properties that may differ in different thickness regimes [3,10,16,[28][29][30]. Consequently, we terminated the deposition experiments after different numbers of potential cycles such that the resultant films were of comparable thickness (i.e.…”

“…At the upper bound, the round trip for the acoustic wave (to the outer film interface, reflection, and back to the electrode) is 4δ, at which point the intensity of the reflected wave is less than 2% of that for the outgoing wave, so signal quality becomes limiting. (involving progressive or instantaneous nucleation, 2D or 3D growth and the presence of diffusional control, according to the electrolyte); (ii) stability differences (due to differing anion lyophilicity [3,40]) in ion pair formation between the anion and the anilinium species produced during monomer oxidation; or (iii) the Gibbs energy change associated with ion formation in aqueous solution [30], which follows the order SO 4 2-< Cl -< NO 3 -< ClO 4 -for polyaniline salt formation. We do not duplicate these efforts by pursuing the origins of these effects, but rather extend the investigation by exploring their consequences in terms of materials properties.…”

“…Polyaniline is a conducting polymer that has attracted considerable research interest [1][2][3][4][5][6], notably with regard to its chemical [7], electrochemical [8,9] and optical [4,9] properties. In pursuit of understanding these properties based on the underlying elementary processes, detailed studies have been reported of various features of redox switching dynamics [3,8,[10][11][12][13][14] and polymer structure [3,10,[15][16][17].…”

“…In pursuit of understanding these properties based on the underlying elementary processes, detailed studies have been reported of various features of redox switching dynamics [3,8,[10][11][12][13][14] and polymer structure [3,10,[15][16][17]. In contrast, polymer dynamics have received rather less attention; here we focus on this aspect of polyaniline behaviour, via an exploration of film viscoelastic properties.…”

“…However, there are a number of studies which indicate that the structure and properties of polyaniline films show significant dependence on the background electrolyte composition, notably concentration and the identity of the "dopant" anion [16,19]. Based on SEM images [3,16] and electrochemical quartz crystal microbalance (EQCM) data [3,10,16] of polyaniline films, it has been proposed that anions fall into two categories. Empirically, so-called "class 1" anions (BF 4 -, ClO 4 -and CF 3 CO 2 -) lead to compact films, while so-called "class 2" anions (SO 4 2-, NO 3 -and Cl -) lead to more open films [16]; however, the underlying rationale for this distinction is not clear.…”