Voltammetric Manifestation of the Ultraslow Dynamics at the Interface between Water and an Ionic Liquid

Abstract

The ultraslow relaxation (on the order of minutes) of the electrical double-layer structure, related to a change in the phase-boundary potential across the interface between water (W) and the ionic liquid (IL) trioctylmethylammonium bis(nonafluorobutanesufonyl)amide ([TOMA(+)][C(4)C(4)N(-)]) (Y. Yasui et al., J. Phys. Chem. B. 2009, 113, 3273), appears to be invisible in the transfer of tetrapropylammonium ions across the [TOMA(+)][C(4)C(4)N(-)]|W interface, provided that the charging current, which shows an unusual dependence on the voltage scan rate, is subtracted to obtain the faradaic current. This counterintuitive observation can be explained by the differences in the timescales of the fast and slow components of the relaxation dynamics of the electrical double layer on the IL side (ms and min). In contrast, the effect of the slow dynamics becomes surfaced in ion-transfer voltammetry when the ion is surface-active. The transfer of pentadecafluorooctanoate across the [TOMA(+)][C(4)C(4)N(-)]|W interface is irreversible, which is attributable to the self-inhibition of pentadecafluorooctanoate ions transferred to the IL phase. This process is likely to be affected by the ultraslow structural change of the IL side of the interface.

Differential pulse stripping voltammetry of moderately hydrophobic ions based on hydrophobic ionic liquid membranes supported on the Ag/AgCl electrode

“…80 mV at v = 5 mV s À1 , is greater than that expected in a diffusion limited ion transfer, it is likely that the transfer of C 6 F 13 COO À is electrochemically reversible, as is the transfer of TPrA + . Incidentally, it is interesting to see that both surface-inactive TPrA + and surface-active C 6 F 13 COO À seem to be transferred across the interface without any apparent anomaly in voltammograms, in contrast to the transfer of the latter ion across the interface between nongelled [TOMA + ][C 4 C 4 N À ] and an aqueous solution, where the Marangoni-type turbulence is reported [39], as is commonly seen in the transfer of surface-active ions across the free (nongelled) liquidjliquid interface [40][41][42][43][44]. It seems that the gelation of one side of the two phases is enough to suppress, at least the macroscopic convective motion of the nongelled phase, the aqueous phase, in the present case.…”

“…4 and 6, we presume that the deviation from the linearity beyond c = 200 is likely to be due to the limited solubility of TPrA + and C 6 F 13 COO À ions in the gelled [TOMA + ][C 4 C 4 N À ] layer. In fact, at the interface between the non-gelified [TOMA + ][C 4 C 4 N À ] and the 0.1 mol dm À3 LiCl aqueous solution, we found that the peak current in cyclic voltammograms for the transfer of pentadecafluorooctanoate (C 7 F 15 COO À ), a homologue of C 6 F 13 COO À , did not grow in proportion to the bulk concentration of C 7 F 15 COO À in the aqueous phase and ascribed the suppression of the peak current to the self-inhibitive transport of C 7 F 15 COO À [39].…”

Simple Ion Transfer at Liquid|Liquid Interfaces

“…Water|trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide interface: pentadecafluorooctanoate and TPrA + [436].…”

Array of water|room temperature ionic liquid micro-interfaces

“…Conventional experiments are performed with a water phase in contact with an organic phase, usually 1,2-dichloroethane or nitrobenzene [11]. Most of the W|RTIL studies so far have focussed on very hydrophobic salts that are solid at room temperature, with a few recent reports of RTILs that are liquid at 25 o C [8,12]. The work reported so far has been performed at single interfaces of milli- [9,12], micro- [7] or nano- [8] metre dimensions.…”

“…Most of the W|RTIL studies so far have focussed on very hydrophobic salts that are solid at room temperature, with a few recent reports of RTILs that are liquid at 25 o C [8,12]. The work reported so far has been performed at single interfaces of milli- [9,12], micro- [7] or nano- [8] metre dimensions. RTILs have also been used in a solid-supported polyvinylidenefluoride membrane sandwiched between two aqueous phases [13].…”