Resistive-Type Humidity Sensors based on PVP-Co and PVP-I2 Complexes

DE QUEIROZ,A.A.A.; WERNER SOARES,D.A.; TRESNIACK,P.; ABRAHAM,G.A.

JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS

John Wiley & Sons, Inc.

Lugar: New York, USA; Año: 2001 vol. 39 p. 459 - 469

0887-6266

Poly(vinylpyrrolidone) films containing cobalt chloride or iodine were investigated in order to obtain information on the electrical dependence of the relative humidity at room temperature. FTIR, UV-VIS and fluorescence spectroscopies were used for characterization of PVP-I2 and PVP-Co complexes. The infrared spectroscopy revealed a structural change of both shape and intensity of the carbonyl and lactam bands,  indicating the formation of the ion-coordination polymer. It was observed a decrease  of the PVP fluorescence with iodine or cobalt doping  that may be associated to the formation of charge transfer complexes. The J-E curves for pure PVP, PVP-I2 and PVP-Co  films obey the ohm law at lower voltages, deviate from the linear response at higher voltages and finally display the breakdown behavior.   It was observed an  increase in current density of the PVP matrix with iodine or cobalt  doping 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 polar side group of PVP. The electrical conductivities of the polymeric complexes were very sensitive to the environmental humidity. An explanation of humidity-sensing behavior of the PVP-I2 and PVP-Co complexes is attempted to the capacity of the dopants iodine and cobalt, respectively,  to give additional charge carriers.