Mechanism Analysis and Application of Thermally Stimulated Currents in Hetero LB films

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Hetero Langmuir-Blodgett (LB) films consisting of alternating monolayrs of amphiphile with large permanent dipoles and long-chain fatty acid take non-centrosymmetrical structure with dipoles oriented toward one direction, and they are amenable to be used for pyro- or piezo-electric elements. In particular, the stimulated current generated by the thermal impulse can be used as an infrared sensor. The origin and the structure-relationship of this current was investigated using hetero LB films of phenylpyrazine derivatives and fatty acids. The large stimulated currents that flows when the hydrocarbon chain is disordered changed its sign, experiment by experiment. Thus, for its utilization as a sensor, we have to use the absolute value change of the current. On the other hand, the pyroelectric current which flows at relatively low temperature, is always positive at around -60ﾟC, but it changed to negative at -20-0ﾟC depending on the compound. In the case of polyion complex between pyrazine derivative and water-soluble cationic polymer, the pyroelectric coefficient did not increased because of the cancellation of increased freedom by the orientation decrease.