Sorption of water and organic solutes in polyimide films and its effects on dielectric properties

Abstract

The effect of structure on the sorption kinetics of water and of various organic solutes into polyimide (PMDA‐ODA) thin films was studied. The major techniques employed include measurements of sorption kinetics, density, and dielectric relaxation. More solute uptake, lower densities and higher diffusivities were observed for films cured at lower temperatures. By measuring both changes of mass and of density, the volume expansion of the polymer due to each solute was obtained; this was found to be proportional to the molar volume of the solute. The two dielectric relaxation peaks (denoted by γ1 and γ2) due to water (and other solutes) were studied in detail to obtain the relevant activation energies and the separate dipole moments. While water and methylene chloride appear in both γ1 and γ2 configurations, methyl and ethyl alcohol appear mainly as γ2, while acetic acid is primarily γ1. It was concluded that the γ1 configurations are relatively homogeneously distributed throughout the polymer, involving loose bonding to the polymer structure, while the γ2 configurations involve small clusters, probably chains of molecules. © 1993 John Wiley & Sons, Inc. Copyright © 1993 John Wiley & Sons, Inc.