Dielectric properties of polyamide-imide

• Published in: Journal of physics. D, Applied physics Vol. 46; no. 18; pp. 185302 - 1-8
• Main Authors: Diaham, S, Locatelli, M-L
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 08.05.2013; Institute of Physics
• Subjects: Breakdown; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Decoupling; Dielectric breakdown and space-charge effects; Dielectric properties; Dielectric properties of solids and liquids; Dielectric strength; Dielectrics, piezoelectrics, and ferroelectrics and their properties; Diffusion in solids; Engineering Sciences; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Fragility; Glass transitions; Imides; Physics; Polyamide-imides; Self-diffusion and ionic conduction in nonmetals; Specific phase transitions; Temperature dependence; Transport properties of condensed matter (nonelectronic); Temperature dependence; Liquid state; Polarization; Dielectric properties; Ionic conductivity; Glass; Fragility index; Space charge; Glass transition; Relaxation; Arrhenius equation; Plasma transport processes; Non linear effect; Activation energy
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/46/18/185302

The dielectric properties of poly(amide imide) (PAI) films are investigated in a large temperature range. A moisture-dependent relaxation (γ-relaxation between −100 °C and 20 °C) and a non-cooperative local dipole relaxation (β-relaxation between 40 °C and 200 °C) display an Arrhenius-type behaviour with an activation energy of 0.50 eV and 1.22 eV, respectively. In the near glass transition (Tg) region at 277 °C, a relaxation process (α-relaxation) occurs due to cooperative segmental motions of the chains and follows a non-linear Vogel-Fulcher-Tamman (VFT) temperature dependence with a strong fragility. Simultaneously in the same temperature range, both a conduction process (σ-conduction) and an electrode polarization phenomenon (ρ-relaxation) are also present. The σ-conduction also follows a VFT behaviour but it possesses a lower fragility in the above-Tg region. This discrepancy is assigned to a partial decoupling between ionic transport and segmental chain motions. The dielectric strength of PAI films exhibits a negative temperature dependence. The near-Tg region corresponds to a change from a thermal breakdown mechanism to an electromechanical breakdown due to the glass-liquid phase transition. Above Tg, the formation of a space-charge probably also involves an electro-thermal breakdown mechanism.