Ionic conductivity zwitterionic liquids

The polymerized ionic liquid (IL) shows great promise for diverse applications. Some polymerization methods have already been oriented toward specific applications. Polymerized ILs are useful in polar environments or where there are ion species for transport in the matrix. Amphoteric polymers that contain no carrier ions are being considered for several porposes in polymer electrolytes. Zwitterionic liquids (ZBLs) were introduced in Chapter 20 as ILs in which component ions cannot move with the potential gradient. ZILs can provide ion conductive paths upon addition of salt to the matrix. It is therefore possible to realize selective ion transport in an IL matrix. If the resulting matrix can form solid film over a wide temperature range, many useful ionic devices can be realized. This chapter focuses on the preparation and characteristics of amphoteric IL polymers. 

Finally, the most recent promising classes in the field of SPEs are the zwitter-ions, identified as Li ion dissociation enhancers , namely ionic liquids where both the anion and cation are immobilized on the same structure. If dispersed into proper PEO-like polymers, the zwitterionic compounds may increase the ionic conductivity of the polymer electrolytes [80]. In case of addition of l-butylimidazolium-3-(n-butanesulphonate) dissociator to Lithium methylacrylate copolymers, for instance, the ionic conductivity achieves a maximum close to 0.6 m cm at 30 °C, in presence of a Li" mole fraction in the copolymer of about 0.050. 

The idea was to increase the lithium transfer number, which is low in most of ILs, IL-salt mixtures, or IL-acid mixtures. Zwitterions with imidazolium cations covalently bound to anions, such as sulfonate, carbonate, imide, or borate, are solids at room temperature, despite their IL-like structure mixing with bis(trifluoromethylsulfonyl) imide, however, leads to blends that are liquid at room temperature. The organoborate-containing zwitterion-lithium salt mixture (Figure 29.3) displays a high lithium transfer number of 0.69, a high-ionic conductivity of 3.0 x 10 S cm at 50°C, and a low glass transition temperature (-35°C). 

A remarkable increase in the rate was observed when the reaction was conducted in ionic liquids instead of CH3CN (Fig. 13). The rate increased by 11 times in [BMIM]BF4 and 34 times in [BMIM]PF6. Furthermore, the product yield was significantly enhanced in [BMIM]PF6 (65%), and this value is considerably higher than that in CH3CN (35%) and is comparable to that of characterizing the neat reaction. The enhanced reaction rates in the ionic liquids were attributed to a shift in the equilibrium favoring stabilization of the zwitterionic intermediate. 

During the last 8 years [82, 83], various types of functionalized ionic liquids (Fig. 13) expressly categorized as being task-specific ionic liquids have been designed and synthesized for specific purposes such as catalysis, organic synthesis, separation of specific materials, as well as for the construction of nanostructure materials and ion conductive materials, etc. The salts are defined as functionalized ionic liquids when they are ionic liquids in which a functional group is covalently tethered to (1) the cation, (2) the anion, or (3) a zwitterionic form of the salt. It is typically the cation that bears the reactive moiety. In fact, instances in which the anion comprises the active constituent are few. 

Rondla R, lin JCY, Yang CT, Lin IJB (2013) Strong tendency of homeotropic alignment and anisotropic lithium ion conductivity of sulfonate functionalized zwitterionic imidazohum ionic liquid crystals. Langmuir 29(37) 11779-11785. doi 10.1021/la402336n... 

The phosphonium ILs (tetradecyl(trihe)grl)phosphonium chloride, tetra-decyl(trihexyl)phosphonium deeanoate, tetradecyl(trihe q l)phosphonium dicyanimide, tetradecyl(trihe qrl)phosphonium bis(triflamide)) have been considered as solvents for CO2 capture using triethylendiamine (TEDA) by Clyburne et al Binary systems composed of two ILs were reported to generate erystalline ion pairs. Ohno and co-workers used zwitterions to investigate the ion pair effect. The addition of a phosphonium type zwitterion (obtained by quaternisation of tri-n-oc(ylphosphine with 1,4-butanesultone) to a typical amino acid ionic liquid such as l-Ethyl-3-methylimidazolium leucine, gave a thermotropic and ion conductive gel. 

---