Application of PVDF-[BMIM][PF6] blends as the active material in screen-printed interdigital capacitors for temperature sensing

This work shows a method to fabricate interdigital capacitors having tunable sensitivity to temperature and stable behavior pointing to the application of ionic liquids (ILs) as fundamental building blocks in capacitive devices for temperature sensing in proximity conditions. Polyvinylidene fluoride (PVDF) in blend with 1-Butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) has been deposited by drop-casting from a N,N-dimethylformamide solution to be utilized as dielectric material in screen-printed interdigitated capacitors. Capacitance and conductance trends versus temperature have been analyzed and compared to bare PVDF dielectrics. The inclusion of [BMIM][PF6] in PVDF-IL blends increases the AC capacitance of the device and its sensitivity to the temperature in the examined range (+20°C to +110°C). AC measurements performed at 100kHz have shown good electrical stability for PVDF-IL blends also when measured in ambient atmosphere. As a drawback, an increase in [BMIM][PF6] concentration resulted also in an increase in AC conductance which exhibits an Arrhenius activation with temperature. Such behavior has been attributed to the increase in ion concentration and ionic mobility with temperature. The work also shows the presence of a limit value for the activation energy of AC conductance for higher concentrations of the ionic liquid.