Ionic conductivity polymer brushes

The difference in ionic conductivity can be attributed to the difference in freedom of the imidazoUum cation. This effect has already been confirmed empirically in our laboratory [11, 12]. For a simple system such as l-ethyl-3-vinylimidazolium TFSl, the ionic conductivity decreased by about four orders upon polymerization. The ionic conductivity of IL polymer brushes having PEO or hydrocarbon chains as spacers between the vinyl group and imidazolium salt are almost the same before and after polymerization. In spite of their rubberlike physical properties, IL polymer brushes had excellent ionic conductivity, around 10 " Scm , at room temperature. Details of the IL polymer brushes are given in Chapter 31. The ionic conductivity of P3 and P4, in which the imidazolium cation is fixed to the main chain, was very low even after salts were added to the matrix. P5 and P6 having the counter anion on the main chain displayed an ionic conductivity fom orders higher than P3 or P4 (about 10 S cm at 50°C). The distance between the vinyl polymer and the imidazolium cation is important for the high ionic conductivity in IL polymers. 

Figure 31.4 Effects of HC spacer iength (n) on both the ionic conductivities (A- the data of P(EVImTFSI) was also shown as reference) and Tg s for IL polymer brushes P(c TFSi).

Essentially all these experimental methods apply when we deal with high-porosity multipore membranes, which are the majority of the cases. However, polymer brush decoration of single nanometric pores on macroscopic membranes has been examined lately [8]. A quite interesting method for the characterization of this system is the measmement of the ionic current that flows through the channel in an electrolyte solution under different electric potential differences. The current-voltage (TV) response of the system can be correlated to the conductance of the polymer-decorated channel and consequently to the effective free cross section of the pore-brush structure. 

Yoshizawa M. Ohno H. (2001). Synthesis of molten salt-typ)e polymer brush and effect of brush structure on the ionic conductivity, Electrochimka Acta, vol.46, n°10-ll, pp.1723-1728, (March 2001), ISSN 0013-4686... 

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