Polyimide ionic conductivities

Implications of Electronic and Ionic Conductivities of Polyimide Films in Integrated Circuit Fabrication... 

Membranes consisting of sequenced sulfonated naphthalenic polyimides (ionic block length of 5) also exhibit higher conductivity and A values... 

Figure 20.5 Temperature dependence of ionic conductivity of composite membrane based on sulfonated six-membered polyimide with an lEC of 2.15 meqg". Reproduced with permission from Ref. [21).

Abstract Sulfonated polyimides have been designed to be used as proton conducting membranes in fuel cells. These materials present most of the required properties for this application, including a high level of ionic conductivity, a low gas and methanol permeability, and good mechanical properties. However, they exhibit a low stability when immersed in liquid water and in hydrogen peroxide solutions at elevated temperature due to a high sensitivity of the imide functions to hydrolysis. The aim of this article is to review the different routes of synthesis, the membrane-specific properties, the structural and transport property characteristics, and finally their behavior in fuel cells in terms of performance and stability. 

Moreover, sulfonated polyimides (SPIs) have been used to prepare polymer electrolyte manbranes for nonhumidified fuel cells by the addition of a protic ionic liquid, diethylmethylammonium trifluoromethanesulfonate [demaJCCFjSOs] (See Fig. 9.6) [78, 79]. The uniform, tough, and transparent membranes have good thermal stability (>300 °C) and ionic conductivity (>10 S cm with an ionic liquid content higher than 67 %) under anhydrous conditions. A current density higher than 240 mA cm is achieved with a maximum power density of 100 mW cm at 80 °C when using a membrane in the H2/O2 fuel cell operation under dry conditions. 

The increasing importance of multilevel interconnection systems and surface passivation in integrated circuit fabrication has stimulated interest in polyimide films for application in silicon device processing both as multilevel insulators and overcoat layers. The ability of polyimide films to planarize stepped device geometries, as well as their thermal and chemical inertness have been previously reported, as have various physical and electrical parameters related to circuit stability and reliability in use (1, 3). This paper focuses on three aspects of the electrical conductivity of polyimide (PI) films prepared from Hitachi and DuPont resins, indicating implications of each conductivity component for device reliability. The three forms of polyimide conductivity considered here are bulk electronic ionic, associated with intentional sodium contamination and surface or interface conductance. 

On the other hand, electrical impedance measurement of bacterial suspensions (.Listeria innocua) was carried out on a Si-glass chip. This method was used to perform a cell viability test. This is because the metabolic products produced from viable cells modify the ionic strength of a low-conductivity medium, significantly altering its electrical characteristics. Later work also involved the detection of the presence of small numbers of bacterial cells in a Si chip 100 L. innocua cells, 200 L. monocytogenes cells, and 40 E. coli cells [93,885], In another report, impedance spectroscopy has been used for analysis of erythrocytes in a glass-polyimide chip [886]. 

PANI has been doped with poly(amic acid) in order to obtain an all-polymer conducting material, by Angelo-poulos el a . [337]. Its structure has not been investigated, but the authors present x-ray diffraction results for cured specimens, in which polyimide formation has taken place at the expense of the carboxylic acid groups. The diffraction is structureless there is no indication that the elimination of the ionic interaction leads to phase separation of the polymers. 

Recently, conductive epoxy resins and polyimides have been used as die-attach adhesives. The chloride ion contents of polyimides are inherently lower than those of epoxies. However, these adhesives are more expensive, have lower bond strength, and are more difficult to cure. Epoxies with low contents of ionic impurities, including chloride anions and sodium and potassium cations, have been available since 1981. These materials are fast curing and have excellent high-temperature strength and a glass transition temperature of up to 200 °C. 

---