ELECTRICAL-CONDUCTIVITY OF SYNTHETIC DOPA-MELANIN POLYMER FOR DIFFERENT HYDRATION STATES AND TEMPERATURES

The dependence of the d.c. conductivity on the hydration and temperatu re (293-343 K) for synthetic DOPA-melanin polymer is presented. The hy dration stare of the melanin has been changed by varying the humidity conditions around the sample. It has been shown, that in the range of relative humidity values (0-100%), changes in the hydration state of m elanin have predominant influence on electrical conductivity (10(-13)- 10(-5) S cm(-1)) in comparison to temperature. The influence of the t wo forms of water on the conductivity-the first form adsorbed mainly o n the melanin surface and easily removed by drying, and the second one incorporated into the inner structure of the polymer, has been invest igated. The temperature dependence of the conductivity in vacuum (0.8 and 0.04 mb) and thermal activation energy values (0.49-0.76 eV) for c ooling and heating curves have been determined. The relationship betwe en thermal activation energy and preexponential factor sigma(o) (compe nsation effect) and possible charge transport mechanisms are discussed .