Studies of Ionic Interactions in Poly(propylene glycol)4000 Complexed with Triflate Salts

Abstract

In aprotic electrolytes and, in particular, in most polyether-salt systems the molar conductivity increases dramatically with increase in salt concentration from a minimum at low concentrations to an unexpected high maximum. Such increases in conductivity are larger than would be accounted for by Fuoss-Onsager type transport theories in which complete dissociation is assumed. Examples can be found in poly(propylene glycol) (PPG) complexed with triflate salts. The series MCF 3 SO 3 /PPG4000 (M ) Li, Na, NH 4 , ND 4 ) has been studied and illustrates the effect of cation on the value of the maximum molar conductivity and the rate of increase of molar conductivity with increase in concentration. Particular attention has been paid to the previously reported enhancement of the ionic conductivity for ND 4 CF 3 SO 3 /PPG4000 electrolytes over that of NH 4 CF 3 SO 3 /PPG4000. Detailed infrared and Raman studies of the polyether C-O-C vibrations and of the salt vibrations have been carried out as a function of temperature (FT-IR) and salt concentration (FT-IR and FT-Raman). Spectral data are reported which show that the polarizability of the anions is effected differently in chemical coordination processes in these ammonium electrolytes than are the dipole moments. We interpret the results in terms of ionic interactions and attribute the enhanced conductivity for the deuterated electrolyte to an increased ionic mobility due to a looser association of the ND 4 + cations to the CF 3 SO 3anions leading to shorter lifetimes of the various associations of ions. We comment on the ionic interactions that have been previously proposed to explain the observed increase in molar conductivity and propose an additional concept, i.e., that with increase in salt concentration there is an increase in the rate of exchange of cations between ion pairs and higher aggregates and between anion-associated sites and those ether oxygen sites to which the cation is less tightly coordinated.

Lithium transference number measurements and complex abilities in anion trapping triphenyloborane–poly(ethylene oxide) dimethyl ether–lithium trifluoromethanesulfonate composite electrolyte

“…positively and negatively charged triple ions. Higher aggregates were described in glyme-triflate systems [22] and in lithium perchlorate systems [23]. We support our opinion that triple ions concentration has significant effect on the conductivity.…”

Ionically conducting polyether composites

“…The NH4+ cations are less tightly bound to the polyether chains as was shown from FT-IR and Raman measurements (12,16).…”

“…FT-IR experiments (12) showed the formation of (SCN-), dimers as well as the co-coordination of NH,' by both PEO and PAAM. It is also evident from FT-IR experiments (12,16) that NH,' cations are more loosely bound to polyether oxygens than are Li' and Na' , which is an explanation for the higher conductivities measured for NH4SCN-doped composite systems. Despite intensive studies the exact mechanisms for ionic conduction in electrolytes containing NH,SCN is still unknown.…”

Multiple charging of poly(propylene glycol) by binary mixtures of cations in electrospray

“…However, the complex formation between metal ions and PPG is affected by many factors such as the solvent environment, the counter ions, the polymer dynamics, and local conformation of PPG, etc. [11,16,17]. Therefore, the discrepancy in the trends may be due to MS sampling, the different solvents, and counter ions used as well as different local conformation and polymer dynamics of PPG.…”