Solvent-induced local deformation zones in polyimide films adhered to a rigid substrate

Abstract

Thin films of a polyimide (Ciba-Geigy XU293) adhered to rigid substrates developed special type of local deformation zones when immersed in xylene. These deformation zones were initiated because of the presence of the combination of xylene and the equi-biaxial tension resulting from the drying process. Their microstructure was strongly influenced by the local bonding to the substrate. In the bonded regions, the zones resembled a narrow trench containing deformed but unvoided material. In the unbonded regions, complicated fibrillar structure was observed in the much wider zones. Although they retained a smooth surface on the face in contact with the substrate in the bonded regions, the deformation zones released a significant amount of stress. The stress release was measured by a photo-elastic method and was found to be in excellent agreement with that calculated from the local thickness change assuming simple elasticity. Although not cracked, there were lines of weakness; after long soaking times the films cracked and delaminated along the defects.