A Study On The Molecular Motion And Charge Storage Of Pvp

Polyvinyl Pyrrolidone (PVP) is a highly polar polymer. The pyrrolidone ring in PVP molecule contains a double-bond carbonyl, which connects to the main chain through an amide bond. This active lactam group, at certain temperatures, will react with a number of substances and generate charge-transfer complex; this group also gives PVP good charge storage capacity. The knowledge concerning the charge storage and transport of PVP electret is highly valuable for some industrial applications.This paper studies the molecular movement and space charge of PVP electret using TSDC method. And the PVP sample used in the experiment is PVP K30 series with a molecular weight of 40000. An in-depth research was accomplished by changing the polarization field strength, polarization temperature and heating rate; and dielectric relaxation method was used as a supplementary measurement in studying the molecular motion of PVP to verify the results of TSDC method:1. The TSDC spectra of PVP electret above room temperature shows three peaks:βpeak which originates from side-group relaxation,αpeak which corresponds to the relaxation of the frozen dipoles on the molecule chain segments during glass transition, andρpeak which is attributed to the detrapping of the trapped space charge under thermal stimulation. When the polarization field strength and temperature change,βpeak andαpeak's positions remain unchanged, while their peak values change proportionally to polarization temperature. As forρpeak, its position does not change with the variation of polarization field strength, while its value increases with the increase of field strength, but the relationship is nonlinear. When the polarization temperature increases,ρpeak moves to higher temperature, the peak value decreases, and the space charge storage capacity of the sample gradually weakens because the high temperature allows more charge to detrap. With the increase of the heating rate, all three peaks move towards higher temperature, and their peak values also increase by various degrees. However, the activation energy does not change, enabling us to calculate the values of the activation energy of the three peaks.2. The magnitude of space charge trapped in PVP's bulk traps is huge, and the trap depth is relatively larger than that of non-polar polymers. This is due to the highly polar side group of PVP molecular.3. The dielectric spectra of PVP at 40~160℃, 63.1Hz~4M Hz is characterized by three obvious relaxation processesγ,βandα. With fitting software based on HN formula,γpeak,βpeak,αpeak and dc conductivity were separated from the dielectric frequency spectra, and several important parameters were calculated, including the relaxation strength, relaxation time and dc electrical conductivity. According to the Arrhenius formula, a figure was drawn to show the relationship between the relaxation time and temperature ofγrelaxation andβrelaxation, and the activation energy of the two relaxations were obtained to verify the results of TSDC measurement. Besides, VTF equation was applied in fitting and calculating the glass transition temperature of PVP when the heating rate is infinitesimal. The result is in accordance with the rule that the glass transition temperature lowers with the decrease of the heating rate.