Complex dielectric response and EDL characteristics of different types of ionic liquid iron oxide nanofluids (ionanofluids)

Abstract

Ionic liquid based magnetic nanofuids (ILMFs), an important subclass of ‘IoNanofuids’, have promising prospectus in numerous technological fields. Herein, we have investigated on the dielectric response and ac conductance behaviour of 1 wt% iron oxide-based ILMFs synthesized using pyridinium-based ILs viz., 1-Butyl-4-methylpyridinium tetrafuoroborate (A), 1-Butyl-4-methylpyridinium chloride (B), 1-Butyl-4-methylpyridinium bromide (C) and 1-Butylpyridinium bromide (D), and having variable stability. The dielectric permittivity exhibited a strong correlation with temperature and frequency, especially at low frequency ranges. Havriliak-Negami (H-N) function was plotted for all the four ILMFs which demonstrated a complex dielectric behaviour. The complex dielectric responses (in the range between 10−1–107 Hz) of these ILMFs at various frequencies and temperatures showed two relaxation processes following either Debye or non-Debye nature. The ILMF synthesized in B and D were the stablest. In B, two relaxation processes at 104 Hz and 6 × 102 Hz were observed (at 373.15 K), the temperature dependence being much stronger for the second process. Cole-Cole processes are observable in both relaxations. α parameters varied in the range 0.8 – 1.0 and 0.62 – 0.9 for first and second relaxation process respectively and β parameter equal to 1 at all temperature range for both relaxation processes. In ILMF synthesized using D, Debye relaxation with two relaxation processes were observed closer at 9.1 × 103 Hz and 1.1 × 103 Hz. All the α and β parameters were 1 or 0.99 indicating same relaxation time for all molecules. With D having higher anion-cation interaction energy, Debye process could be observed. The alternating current (AC) conductance of these ILMFs tends to increase with increase in temperature as well as frequency of applied field till 105 Hz after which it decreases.