Electrical and optical properties of fullerenol Langmuir-Blodgett films deposited on polyaniline substrates
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abstract
The synthesis of fullerenol with various degrees of hydroxylation and the use of a low hydroxylated product to form stable Langmuir films are reported in this work, along with the optical and electrical properties of Langmuir-Blodgett (LB) films obtained on glass and polyaniline (PANI) substrates. The data suggest that an average of 9-12 hydroxyl groups are bound preferentially on one side of the C60 cage and this allows the formation of stable two-layer films at the air/water interface. The large anisotropy of the hydroxylated molecule provides organized LB films of the type substrate-(D-C60-D-C60-)n, with D representing the hydroxyl groups. The electrical conductivity of LB films deposited on glass is equivalent to that reported for highly conductive polymeric C60 but several orders of magnitude higher than that for disordered fullerenol pellets. UV-vis absorptions provide evidence that fullerenol layers cause the deprotonation of PANI, rendering a polymer with low conductivity. The loss of conductivity disagrees with the behavior expected for a donor (PANI)/acceptor (fullerenol) interface, even though current-voltage (I-V) curves of fullerenolLB/PANI junctions indicate some degree of electrical rectification. Additionally, transients observed at large bias on the I-V curves agree with the reported proton conductivity of fullerenol.
