PREPARATION AND CHARACTERIZATION OF HUMIDITY SENSOR BASED ON POLY（3-ALKYL）PYRROLE CONTAINING PHOSPHONIC ACID GROUPS

Poly（3-alkyl）pyrroles containing phosphonic acid groups with different alkyl segment lengths were chemical synthesized and the properties were measured by FTIR and UV-Vis spectroscopy. FTIR and UV-Vis results showed that the synthesized polymers were in a low doping level through chemical polymerization. By spin-coating on the surface of substrates, the polymer can be used as a humidity sensor. The change of DC electric current of the polypyrroles varies with the chain length of the alkyl substituents. The capacitance increases with the increase of the humidity and resistance decreases with the increase of humidity. This result is different from that ofpolypyrrole without alkyl substituents due to the influence of the phosphonic acid group. The sensor showed the resistive-type at high relative humidity, and the capacitive- type at the low relative humidity. The sensor exhibited very fast response to the change of environment humidity.