Attempts to measure ion mobilities in EHD liquids by the time-of-flight method

Two different kinds of attempts were made to measure ion mobilities in EHD liquids by using the time-of-flight technique. The first attempt was a reverse polarity method which was similar to that used by L. Yang et al. [5]. The stainless steel coaxial cylindrical electrodes with the effective length of 55 mm and the electrode spacing of 1.5 mm were utilized. The purified two sample liquids; hydrofluoroether (HFE7600) and 2, 3-dihydrodecafluoropentane (HFC43-10) with very low dark current (less than 20 pA at 150 V) were used. In this attempt, it is deduced that the mobility value is of the order of 1×10^-8 m²/Vs. In the second attempt, the plate-mesh-plate electrode configuration was employed. One plate was used to apply high voltage pulses and the other plate worked as a counter electrode. The center mesh electrode was kept at low dc voltages. This triode electrode design allows us to monitor the amount of charge injected from the charge injection space to the charge detection space through the mesh electrode during and after the high voltage pulse. Two sample liquids; HFE 7600 and HFC43-10 were used without any purification. Ion drift currents were found to have very long tails. If the tails are included into the drift times, the mobility of ions can be as low as approximately 1×10^-9 m²/Vs in both liquids.