Silica/polyimide-polydimethylsiloxane hybrid films. Thermal and electrical properties

Hybrid films containing silica were prepared using a poly(amic acid) incorporating polydimethylsiloxane segments and tetraethoxysilane via a sol-gel technique and thermal cyclodehydration. The surface morphology of the films was examined by atomic force microscopy and scanning electron microscopy. The free surface energy was evaluated based on contact angle measurements. The films were flexible and showed good mechanical properties. They exhibited high thermal stability with an initial decomposition temperature above 420 A degrees C and a glass transition temperature in the range of 216-223 A degrees C. Dielectric spectroscopy revealed primary alpha(1) relaxation due to the polydimethylsiloxane segments, and three subglass transitions: gamma, beta(1) and beta(2). At higher temperatures, alpha(2) -relaxation that corresponds to the upper glass transition and a conductivity process appeared. The influence of the silica content on the hybrid film properties was examined. Dynamic mechanical analysis revealed similar relaxation processes to those observed by dielectric spectroscopy.