利用PFSE-NMR(pulsed-field-gradient spin-echo NMR)擴散(D)實驗最近被使用來探討離子液體(ILs)的物理性質，結合電化學數據， Watanabe和他的研究團隊介紹了”ionicity”和證實自解離BMIPF6(約80％)在propylene carbonate (PC)進行離子結合。此外，FAB-MS光譜顯露BMI-PF6比較喜歡以帶負電荷型式存在，而不喜歡以帶正電荷方式存在。根據想要瞭解增加影響共溶劑(co-solvents)在離子液體中物理性質的目標，Pregosin研究團隊利用PGSE-NMR 數據和 1H，19F-HOESY 光譜發現了“陰離子橫跨imidazolium平面“且“陰離子漂浮在陽離子附近“的模型。且他們發表另一個陳述“一個陽離子周圍圍繞超過一個陰離子“。這與我們最近提議用超陰離子(hyper anion preference (HAP))來解釋BMIPF6的許多物理性質：(1)陰離子擴散比陽離子擴散對溫度有更高敏感度 (2) cationic transference數目會隨溫度而變 (3) 低的陰離子donicity和高ionicity (4) 高黏度。
在之前的研究我們已經發現1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6) 在2,2,2-trifluoroethane (TFE)中可以增進溶解度，與乙醇比較起來，TFE上的CF3可與陽離子BMI+ interact。這表示“ 陽離子與陰離子擴散的比“ 下降，可以經 1H，19F-HOESY光譜證實。我們已經指出原本PF6–會圍繞在BMI+上的丁基，但當莫爾分率增加為19:1 (TFE:BMI-PF6)時，TFE上的CF3取代原本圍繞在BMI+上丁基的PF6–而增進溶解度。換句話說，原本在BMI+上丁基的PF6–因CF3取代而更靠近BMI+的環上；這個描述當加入更多的TFE時會更接近“astriding model“。

這個研究第一個目的為利用1H，19F-HOESY光譜研究陰離子PF6–漂浮在丁基上BMI-PF6的物理性質。第二個目的為檢查“陽離子與陰離子擴散的比“。BMI+ (D +), PF6– (D –) and TFE (D TFE)在混合物I 到VIII(BMI-PF6/TFE，χTFE=0.25、0.35、0.4、0.45、0.5、0.55、0.65、0.8)的擴散速率利用PGSE-NMR實驗改變莫耳分率(TFE/BMI-PF6)由1:3到4:1來檢查TFE上的CF3對溶解度的改變。用1H，19F-HOESY 光譜和自旋-晶格弛緩 (spin-lattice relaxation times (1H 和 19F))補充不足資訊。

The pulsed-field-gradient spin-echo (PFSE) NMR diffusion (D) experiments have recently been employed to study factors affecting physical properties in ionic liquids (ILs). Combining with electrochemical data, Watanabe and coworkers have introduced the term “ionicity“ and confirmed that the self-dissociatable (near 80%) BMIPF6 proceeds ionic association in the presence of propylene carbonate (PC) cosolvent. Besides, the FAB-MS spectra reported for BMIPF6 reveal that the charged clusters prefer existing in anions to existing in cations. With the aim to understand how physical properties of ILs are affected by adding cosolvents, on the other hand, Pregosin et al. have proposed the models of “anions astriding imidazolium plane“ and/or “anions floating around the cation“ based on PGSE-NMR data and 1H,19F-HOESY spectra. They have also presented the statement,“an individual cation is surrounded by more than one anion.“ We have recently proposed that this hyper anion preference (HAP) approach might be employed to account for numerous physical properties published for BMIPF6, including (1) higher sensitive of anionic diffusivity towards temperatures than cationic diffusivity, (2) temperature-dependent cationic transference number, (3) low anionic donicity and high ionicity and (4) high viscosity.
In a previous study we ascribed the improved miscibility of 1-butyl-3-methylimidazolium hexafluoro-phosphate (BMIPF6) and 2,2,2-trifluoroethane (TFE), compared with that of BMIPF6 and ethane, to the CF3 group since it can interact with BMI+ cations. This is shown by reduced “ratios of cation to anion diffusivities” via PGSE-NMR experiments and further confirmed by 1H,19F-HOESY spectra. We have pointed out that the originally PF6–-surrounded butyl groups of BMI+ cations are seen by the CF3 groups of TFE in the mixture at moar ratio 19:1 (TFE:BMIPF6). In other words PF6– anions are localized near the BMI+ ring system, a description closer to the astriding model as more TFE are added. The first purpose of this work is to investigate the effects of floating of PF6– anions around the butyl on physical properties of BMIPF6 focused on 1H,19F-HOESY spectra acquired for IL/cosolvent systemes.
The second goal in this work is to examine the validity of the approach of “ratios of cationic to anionic diffusivities” proposed earlier in the other work.3a Diffusion coefficients of BMI+ (D+), PF6– (D–) and TFE (DTFE) in mixtures I to VIII, with TFE/BMIPF6 molar ratios increasing from 1:3 to 4:1, measured by PGSE-NMR experiments have been analyzed to examine the function of the CF3 group in assisting the miscibility. 1H,19F-HOESY spectra and spin-lattice relaxation times (1H and 19F) have also been investigated to get supplementary and/or complementary information.

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