The goal of Tokuda et al. 2005 was to observe physical properties of various RTILs including, but by no means limited to, the effect of the varying alkyl chain length on [Rmim][CF3SO2)2N]’s thermal behavior, density, viscosity, self-diffusion coefficients, and ionic conductivity with varying temperatures (which, given our focus on alkyl-chain length for testing the CAE’s accuracy for describing the RTIL fluidity, seems like a great place to start). The most interesting section of this paper, at least to me, is Ionic Self-Diffusion Coefficients which they calculate for both the anion and cation, they use a method called pulsed-field-gradient spin-echo (PGSE) NMR, which from my limited understanding involves determining the diffusion coefficients of the anion and cation individually using NMR, then they use this data to fitted to the Vogel-Fulcher-Tamman (VFT) equation to find the diffusivity and viscosity trends seen in figure 3. My question in this is how does this compare to the CAE model for describing fluidity? For example, in the description of the CAE, it says the “We have previously shown that equations similar in form to eq 3 can be written for the ionic conductivity, diﬀusion coeﬃcient, …” (Petrowsky 2972). Does this mean that the VFT is a competing model for describing fluidity and diffusivity? On pg 6107 they do correlate the diffusivity to the fluidity (or viscosity more accurately) using the Stokes-Einstein equation which makes me wonder what the exact application of the VFT vs the Stokes-Einstein equation and why they choose to use both.
Overall this paper provides a great back-drop for the research I believe we will be doing in the near future, and hope, as I continue to read up on the theory behind these physical properties they will begin to be more clear. Recently I have started looking into the exact nature of PGSE NMR and how it works (which I already found a great introductory manual online for!!). Today and tomorrow though, I expect to be diving into the Galinski et al. 2006 paper on Ionic Liquids as Electrolytes, which from the looks of it has a great section of the basic physical properties (such as melting point, density, fluidity, conductivity, etc) of every RTIL I could ever dream of. This will, hopefully, be especially useful to finding RTILs that can be used in a task-specific manner in order separate metal ions based of their physical properties.