Complex dielectric behavior of polyaniline at microwave and millimeter-wave frequencies

Abstract

A study of the complex dielectric properties at microwave and millimeter-wave frequencies on several polyanilines was performed. The polymers investigated were based on emeraldine salts. The chemically synthesized emeraldine base was protonated with acids of various pH levels. Aqueous HCl (pH range 0.12 to 1.07) and tosylic (pH range 0.22 to 1.13) acids were used. Complex permittivities of the emeraldine base and salts were determined at the X-band and R-band using waveguide measurements. Characterization techniques were developed to reduce the measurement error. This included the electrical determination of the sample holder length and sample position. The real component of the dielectric constant was found to vary from 4 to 131 at X-band and from 3.8 to 1910 at R-band. The dielectric loss spanned three orders of magnitude at X-band and four orders of magnitude at R-band. The frequency dependence was relatively level within each band with a slight decrease in each permittivity component with increasing frequency. The d.c. conductivity ranged from 10 −4 to 10 −1 S/cm for the emeraldine salts. The time dependence of the complex permittivity and d.c. conductivity was examined.