ELECTRICAL CHARACTERISTICS AND ELECTRET BEHAVIOR OF MELANIN

Conventional electrical measurements and the thermally stimulated depolarization current (TSDC) technique were exploited to investigate the electrical conductivity and the electret behavior of synthetic melanins. Our results can be summarized as follows: (i) Melanin contains deep traps at 1 eV and shallow traps giving rise to space charge-limited currents; (ii) all the samples we examined show strong TSDC peaks at 370°-400°K without any applied polarizing field. These are caused by the release of trapped water molecules, the activation energy being about 1.45 eV; (iii) the orientation of water dipoles is partially responsible for the low temperature TSDC peak induced by applied electric field (activation energy 0.32 eV); (iv) the very complex structure of the TSDC plots can be attributed to an irregular distribution of charges and dipoles trapped in the heterogeneous macro-molecules containing various amounts of the indole-5,6 quinone precursors. © 1979, The Electrochemical Society, Inc. All rights reserved.