15 10 5 5 Chemical Shift ppm 0 V 110 V Figure 29 The 6 steps of the third

15 10 5 5 chemical shift ppm 0 v 110 v figure 29 the

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15 10 5 0 -5 Chemical Shift (ppm) 0 V 110 V Figure 2.9: The 6 steps of the third reported eNMR experiment on BMIM TfAc with 5 volume % hexamethyldisilane. As can be seen in figure 2.9 , signal attenuation increases with each step due to convection-induced flows; indeed, the small phase shift of ionic liquids is not visible on the last spectrum with this magnification and further increase in applied voltage was not practical. The phase shifts measured from eNMR with phase compensation from the reference were plotted and the data fit was used to calculate μ (see equation 1.13 on page 12 ). As can be seen from figure 2.11 on page 24 and figure 2.5 on page 19 the second runs deviation in temperature variation from the other two runs can also be seen as a significant difference in convection compensation from the reference compound.
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24 CHAPTER 2. SUMMARY OF RESEARCH Figure 2.10: Plot of eNMR data for BMIM TfAc with 5 volume % hexamethyldisilane. The plot shows the convection compensated phase shifts (reference shifts taken from figure 2.11 ) with linear fits. Figure 2.11: Plot of reference phase shifts that were used to convection compensate the eNMR results for BMIM TfAc with 5 volume % hexamethyldisilane in figure 2.10 . 2.3.3 Calculations Equation 1.13 on page 12 relates phase shift to electrophoretic mobility, μ . With δ , Δ , D and g taken as constant and φ / E , given by the fit for the eNMR data in figure 2.10 as the slope ( k 1 , k 2 and k 3 ), μ cation , can be calculated as the average of μ 1 , μ 2 and μ 3 . For the three experiments, the resulting electrophoretic mobility is then:
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2.3. RESULTS 25 μ 1 = k 1 l γgδ Δ = 0 . 17853 · 0 . 040 1 . 533 · 10 10 · 0 . 451 · 0 . 003 · 0 . 300 = 1 . 277 · 10 - 9 m 2 V · s μ 2 = k 1 l γgδ Δ = 0 . 18409 · 0 . 040 1 . 533 · 10 10 · 0 . 451 · 0 . 003 · 0 . 300 = 1 . 317 · 10 - 9 m 2 V · s μ 3 = k 1 l γgδ Δ = 0 . 20733 · 0 . 040 1 . 533 · 10 10 · 0 . 451 · 0 . 003 · 0 . 300 = 1 . 483 · 10 - 9 m 2 V · s Thus μ cation is taken as 1 . 36 ± 0 . 09 · 10 - 9 ( m 2 V - 1 s - 1 ). Once μ cation and D cation were both known, the effective cation charge of BMIM TfAc could be calculated through equation 1.13 on page 12 as: z cation = 0 . 51 ± 0 . 03 As the nominal charge of the BMIM cation is +1 this gives a degree of dissociation of z cation or 0.51. The acquired result coincides well with those reported by Tokuda et al. [ 1 ] who reported z cation as 0.52.
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Chapter 3 Conclusions As shown in this report BMIM TfAc has an effective charge for its cation of +0.51. This coincides well with the reported value of 0.52 [ 1 ]. As the system is in principle neat it is assumed that the anion charge should be the opposite that of the cation, or -0.51. This is however a point that requires further investigation. The most reasonable path to proceed along is to measure anion electrophoretic mobility through 13 C eNMR. As shown by equation 1.12 on page 11 one needs to keep δ · g · γ constant in order to achieve the same phase shift during an experiment. If γ is then reduced by a factor of 4, by changing nucleus from 1 H to 13 C, g and/or δ need to be increased by a factor 4 to acquire the same phase shift during the experiment. As the system is at 85% of maximum g without changing probe and increasing δ to above 5 ms is not recommended this will in turn require a change to a high-gradient strength diffusion probe. Running
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