Viscoelastic Characterization of Electrochemically Prepared Conducting Polymer Films by Impedance Analysis at Quartz Crystal

Abstract

An electrochemical quartz crystal microbalance is used for a continuous monitoring of the growth of the polymer poly͑3,4-ethylenedioxy͒ thiophene tetrabutylammonium perchlorate ͑PEDOT-TBAP͒, electropolymerized in acetonitrile on a gold electrode of a 10 MHz AT-cut quartz crystal resonator. The surface acoustic impedance of the resonator is analyzed starting from the electrical admittance continuously measured by means of a network analyzer. Changes in the acoustic impedance suggest that a mechanical resonance phenomenon occurs during the electrodeposition. To determine the origin of this effect, the evolution of the physical properties of the coating is analyzed. This analysis shows a significant change of the viscoelastic properties of the coating during the electropolymerization and especially during the time interval of the suspected mechanical resonance. The effect of the surface roughness on the mechanical impedance of the coating is analyzed. This study seems to indicate that the changes in the effective viscoelastic properties of the coating are due to the changes in the surface roughness. The mechanical resonance effect also seems to be more a result of this change in the coating effective viscoelastic properties than of the growth of the coating thickness where coating viscoelastic properties are maintained constant.Polythiophenes are high conductive polymers with high chemical and thermal stability. Due to their high electrical conductivity, polythiophenes find interesting uses in different applications, such as patterned circuits ͑plastic circuits͒, photodiodes, 1 biosensors, 2 antistatic coatings, 3 corrosion protection coatings, 4 etc. However, they have not been extensively used due to the changes of their properties, which have been observed over the course of time when coming in contact with the environment. Moreover, relatively little is known about the mechanical properties, such as shear moduli, of these polymer layers, whose thicknesses can range from some nanometers to micrometers depending on applications.The quartz crystal resonator ͑QCR͒ technique can be useful for estimating these properties and their change during the polymer growth. Furthermore, other effects regarding the macroscopic structure of the polymeric coating can contribute to the sensor response and be analyzed, in particular the roughness effect, intimately related to the porosity and with the hydration grade.Some results in this field were reported by Hillman and coworkers, who described the viscoelastic effects of polythiophenes by means of an electrochemical quartz crystal microbalance ͑EQCM͒, 5-7 including the evolution from gravimetric to viscoelastic response in poly͑3-methylthiophene͒ films 8 and the acoustic phenomenon of film resonance in poly͑3-methylthiophene͒ in contact with liquid electrolyte. 9 The reports of "film resonace" in quartz crystal resonators are almost entirely focused on thiophenes. It has been our interest to report film resonances with poly͑3,4-ethylenedioxy thiophene͒ ͑PEDOT͒ and most importantl...

Solvent effects on the electrochemical p-doping of PEDOT

“…31 Crystal admittance data were acquired at the end of deposition to ensure the film was acoustically thin (''rigid'') and recognizably different from the viscoelastic films studied previously. 1,2,27,28 Following deposition, films were rinsed with CH 3 CN and transferred to monomer-free 0.1 M TEABF 4 /CH 3 CN or 0.1 M TEABF 4 / CH 2 Cl 2 for voltammetric characterization. To ensure complete exchange of electrolyte from that of the deposition solution to that of the characterization solution, films were redox cycled 3-4 times after solution exchange.…”

“…Calvo et al have used the same technique to study PEDOT film deposition. 28 The selection of conditions (notably film thickness) in these experiments ensured that solvation was primarily manifested through its effect on polymer dynamics, parameterized in terms of viscoelastic properties. The present study is complementary to those reports, in that it explores the behaviour of (acoustically) thin films, where viscoelastic phenomena are not manifested to any significant extent.…”

Temperature dependence of the complex shear modulus of cation and anion exchanging poly(pyrrole) films

“…So far, among the studied polymers were: poly(3-methylthiophene) [6], regioregular poly(3-hexylthiophene) [7,8] and poly(3-decylthiophene) [9], poly(3,4-ethylenedioxy thiophene) [10,11], poly(pyrrole) [2], and poly(vinylferrocene) [12] and self-assembled polyelectrolytes [3,4,13,14]. In a typical experiment, the polymer is deposited on a thin (ca.…”

“…(1) can be solved for G 0 and G 00 by using standard programs. While all parameters are measured experimentally, the most accurate procedure for the evaluation of h f still remains a matter of discussion [11,16,17]. Our approach will be discussed in Section 2.…”

“…(1), there are alternative approaches, emphasizing the influence of film roughness [11,[18][19][20].…”