Materials Properties of Conducting Polymers PEDOT:PSS/PVA

Conducting polymers have wide application as a structural and electrically conducting element in MEMS devices. However, the electrical and mechanical properties of the conducting polymers must be well characterized so that applications can be developed. Thus, the overall focus of the research presented herein is the determination of the electrical and mechanical properties of a conducting polymer that consists of a blend of PEDOT:PSS and PVA. This blend is chosen for this study as previous studies have shown that PEDOT:PSS has a relatively high conductivity of approximately 500 S/cm. This is higher than the conductivity of many other conducting polymers such as polypyrrole (PPy), polyaniline (PANI), polythiophene (PT) and polyacetylene (PA) which have nominal conductivities of respectively, 100, 10, 100 and 350--500 S/cm. However, PEDOT:PSS is very brittle and is, therefore, not useable as a structural element in MEMS devices. Blending with PVA offers a straightforward approach to improve the ductility but, at the same time, leads to a reduction in conductivity. Thus, one of the specific goals of the present study is to determine not only the conductivity and mechanical properties of various weight percentage (wt%) blends but also to determine the range of weight percentage of PEDOT:PSS in PVA that leads to acceptable conductivities while maintaining mechanical properties that would enable the blend to be used as a structural element (for example, as an electrically conducting spring) in a variety of MEMS devices.;The DC electrical properties of the films are determined as a function of weight percentage of PEDOT:PSS in PVA using the four point probe method. The film conductivity increased with increasing weight percentage of PEDOT:PSS. Values of the DC conductivity ranges from varied from 10 S/cm to 3.18x10 -5 S/cm for PEDOT:PSS weight percentages of 10 and 100%. In addition, the effect of the conductivity enhancer, N-Methyl-2-pyrrolidinone (NMP), has been studied and found to lead to an increase in conductivity of the polymer blends by 2 to 5 orders of magnitude (depending on the amount of PVA in the blend). This increase is attributed to a conformational change of PEDOT chains.;However, PEDOT:PSS is too brittle to be employed in many applications. The addition of PVA increases the viscosity of the polymer mix making it easier to spin coat and facilitate micrometer-thick conducting polymer films. PVA also enhances the plasticity of the film, but reduces its electrical conductivity. The mechanical properties of the films as a function of weight percentage of PEDOT:PSS are studied using a uniaxial tensile test to characterize the Young's modulus, fracture strain, tensile strength, and plastic deformation behavior of the blends as a function of the weight fraction of the components. The Young's modulus is found to vary from 0.0413 GPa for pure PVA to 1.6323 GPa for a weight percentage blend of 50% and the elongation % at the break point is found to be 111% for pure PVA and 56% for 50 wt% of PEDOT:PSS.;Blending PEDOT:PSS with PVA is a promising route to reach a reasonable trade-off between electrical and mechanical properties. Based on the results of the DC conductivity and mechanical studies, the current work suggests that a PEDOT:PSS/PVA polymer blend with 30--40 wt% of PEDOT:PSS provides the best trade-off of conductivity and ductility. However, for non free-standing films, higher PEDOT:PSS fractions (70 wt%) might be preferable.;Impedance spectroscopy of the films is also studied using a Gamry Potentiostat. The relaxation time constants, permittivity, dielectric modulus are presented and discussed. The equivalent circuit diagrams are also modeled and shown to demonstrate the space charge polarization and conductive mechanism.