Liquid ionic impurities

Apart from halide and protic impurities, ionic liquids can also be contaminated with other ionic impurities from the metathesis reaction. This is especially likely if the alkali salt used in the metathesis reaction shows significant solubility in the... 

For all research carried out with commercial ionic liquids we recommend a serious quality check of the product prior to work. As already mentioned, a good commercial ionic liquid may be colored and may contain some traces of water. However, it should be free of organic volatiles, halides (if not an halide ionic liquid), and all ionic impurities. 

Similar but even more pronounced anionic effects were observed with liquid membranes based on ionophore 80 and exhaustively purified organic solvents (nitrobenzene or 1,2-dichloroethane) but no polymer matrix. The use of such membranes allows to minimize the concentration of ionic impurities that could take the role of anionic sites. For a membrane with ionophore 80, the SHG response... 

This decrease has generally been accepted as an inevitable consequence of plasticization, and it is frequently explained as the migration of ionic impurities through the liquid plasticizer medium (2, 4, 5). 

Nevertheless, it would seem reasonable that, in the absence of any liquid plasticizer medium at all, mobility of ionic impurities would be reduced to such a low level that volume resistivity would remain high. For example, it is well known that polyvinyl chloride can be blended with nitrile rubber, such as Goodrich Hycar 1032 butadiene/acrylonitrile copolymer, and such polyblends are quite soft and flexible without the use of any liquid plasticizer at all (Table VII). 

Haase and co-workers investigated electro-optic and dielectric properties of ferroelectric liquid crystals doped with chiral CNTs [495, 496]. The performance of the doped liquid crystal mixture was greatly affected even by a small concentration of CNTs. The experimental results were explained by two effects (1) the spontaneous polarization of the ferroelectric liquid crystal is screened by the 7t-electron system of the CNT and (2) the CNT 7i-electrons trap ionic impurities, resulting in a significant modification of the internal electric field within liquid crystal test cells. 

As a new class of materials, ionic liquids require special analytical methods. In the case of imidazolium halides and similar compounds the most common impurities are amines, alkyl halides and of course water. Seddon et al. described a method for the detection of residual amines using the strong UV absorbance of copper tetramine complexes. These complexes are readily formed by the addition of Cu2+ ions [24]. The detection of both amines and alkyl halides is possible by NMR spectroscopy but with limited resolution [25]. By far the most powerful analytical method is liquid chromatography combined with UV detection. This sensitive method allows the detection of traces of amines and halides [26]. Unreacted amines can be also detected by ion chromatography combined with a suppressor module. In this case detection is achieved using a continuous flow conductivity cell since amines are protonated and thus detectable. For traces of other ionic impurities ion chromatography is also the most powerful analytical tool [27]. Finally, residual water can be quantified using Karl Fischer titration or coulometry [28]. 

Effect of Possible Ionic Liquid-Inherent Impurities... 

In a preliminary study, the effect of ionic liquid-inherent impurities on the peak area A (and hence the vapour pressure) of a solute was investigated using the example of toluene in [C6mim]Cl, to which either water or 1-methylimidazole were deliberately added to simulate the most likely impurities occurring in ionic liquids. 

Figure 4.12 Increasing evenness of electrostatic charge distribution (red and blue denote and positive partial charges, respectively B3 LYP/6-31 G //AM1 level of theory) [43, 44] minimizes the ability of fluorinated polar liquid c stals to solvate ionic impurities by local electrostatic interactions.

Fig. 2.2-2 Ion chromatography-the method of choice for the quantification of ionic impurities in ionic liquids.

Apart from halide and protic impurities, ionic liquids can also be contaminated with other ionic impurities from the metathesis reaction. This is especially likely if the alkali salt that is used in the metathesis reaction shows significant solubility in the ionic liquid formed. In this case the ionic liquid can contain significant amounts of the alkali salt. While this may not be a problem even for some catalytic applications (since the presence of the alkali cation may not effect the catalytic cycle of a transition metal catalyst) it is of great relevance for the physicochemical properties of the ionic liquid. 

The ions of the liquid or impurities in the ionic liquid may act as reversible or... 

It has also been used to study the second sound resonance in smectic A liquid crystals and measure the compression modulus. For measuring the flexocoefficients (ei — 63) and (ei + 63), hybrid-aligned nematic cells have been used extensively. AC techniques avoid problems associated with ionic impurities, but require elaborate numerical fitting of the data. Some observations on the pnblished measurements of flexo-coefHcients are made in Section 2.4, which ends with a few concluding remarks. 

The question arises what mechanism is responsible for the EHD instability in these polymers Such effects in liquid crystals are the result of the ionic conductivity, The free charge-carrier can appear either due to ionic impurities in the substance, or due to the injection or exclusion of electrons by neutral molecules on electrodes. 

To investigate the role of LCP in the composite on the electro-optical properties, PS[4BC/DM]s with the degree of polymerization of 12 and 40 were used as LCP. In order to investigate the role of LCD in the composite on the electro-optical effect, low molecular weight smectic LC, S2 was employed as a sample of composite in which any LCP was not included. S2 is a binary smectic mixture of low molecular weight liquid crystals as shown in Figure 1. The ionic impurities (Pt catalyst) of about 1000 ppm was added to S2 to unify the condition of electric current effect with the (PS[4BC/DM](n=12, 40)/E7) composites which contain about 1000 ppm of Pt catalyst. 

The introduction of dye molecules into the liquid crystalline host does not change the majority of the properties of the host, provided that not too much dye is introduced (not more than 1-2%). The N I transition temperature of the liquid crystal, the viscous and elastic properties, the electrical conductivity (provided the dye is not ionic and does not contain ionic impurities), the dielectric permittivities, (provided the dye molecule does not have a large dipole moment), and even the refractive indices all remain the same. The only significant change in the properties of the crystal is the appearance of absorption bands in the visible region of the spectrum and a slight increase in viscosity [151]. 

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