Resistive-type humidity sensors based on PVP-Co and PVP-I-2 complexes

Poly(vinylpyrrolidone) films containing cobalt chloride or iodine were inve stigated to obtain information on their possible use as a humidity sensor e lement. FTIR and UV-VIS spectroscopies were used to characterize the PVP-I- 2 and PVP-Co complexes. Infrared spectroscopy revealed a structural change of both shape and intensity of the carbonyl and lactam bands, indicating th e formation of an ion-coordination polymer. The J-E curves for pure PVP, PV P-I-2, and PVP-Co films obey ohm's law at low voltages, deviate from the li near response at higher voltages, and finally display breakdown behavior. A n increase in current density of the PVP matrix with iodine or cobalt dopin g is attributed to the formation of charge transfer complexes. The observed hysteresis of the I-V characteristics implies that there was some standing voltage in the film, which could be attributed to a disorientation of pola r side groups of PVP. The electrical conductivities of the polymeric comple xes were very sensitive to environmental humidity. An explanation of the hu midity-sensing behavior of the PVP-I, and PVP-Co complexes is presented. (C ) 2001 John Wiley & Sons, Inc.