Transient and steady-state conduction in ethyl cellulose (EC)-poly(methyl methacrylate) (PMMA) blends

Transient discharging currents and steady-state conduction in solution-grow n ethyl cellulose (EC)-poly(methyl methacrylate) (PMMA) blends measured as a function of temperature (30-80 degrees C) and field strength (10-100 kV c m(-1)) are reported. Transient currents are found to follow the Curie-Von S chweidler law, characterized by different slopes in short- and long-time re gions, having different decay constant values lying between 0.75-0.99, and 1.68-1.95. The corresponding activation energies are found to increase with time of measurement of discharge current. Isochronal characteristics tie c urrent versus temperature plots at constant times) constructed from the dat a seem to reveal a broad peak observed at 60 degrees C. The dependence of d ark current at different temperatures (30-80 degrees C) in a metal (1)-EC-P MMA blend-metal (1)/(2) system on the applied voltage in the range 10-100 k V cm(-1) has also been studied; the current is found to be strongly tempera ture dependent. Dipole polarization and space charge resulting from trappin g of injected charge carriers in energetically distributed traps and induce d dipoles created because of the piling up of charge carriers at the phase boundary of the heterogeneous components of the blend are considered to acc ount for the observed transient currents. The results of current-voltage me asurement on blends are interpreted to show that the low-field steady-state conduction is ohmic in nature, and in high fields the charge carriers are generated by field-assisted lowering of coulombic barriers at the traps and are conducted through the bulk of the material by a. hopping process betwe en the localized states by a Jonscher-Ansari Poole-Frenkel mechanism. The m odified P-F barrier is calculated to be 1.89 x 10(-19) J (1.18 eV), 1.92 x 10(-19) J (1.20 eV) and 1.95 x 10(-19) J (1.22 eV) for P-1, P-2 and P-3 ble nds, respectively. (C) 2000 Society of Chemical Industry.