Specific Ion Effect on the Growth of PEMs

PSS outer layer, when PDDA is introduced, it forms a layer on PSS surface via the electrostatic attraction. Thus, the mass or layer thickness increases, leading to an increase of —A/. However, the subsequently introduced PSS chains would penetrate into PDDA layer, and they form complexes. Some associated water molecules are released from the multilayer during the complexation, giving rise to a decrease in —A/. Accordingly, more chain interpenetration and complexation 

Cr and HCOJ. Reprinted with permission from Ref. [19]. Copyright 2010 American Chemical Society 

The average values of — Af due to the deposition of PSS ot PDDA for the last four layers as a function of anion species for HCOj, F , CHsCOO, H2PO4, and S04 are shown in Fig. 4.9. It is evident that the deposition of PSS causes more increase in — A/than that of PDDA with the exception of the case of HCOa , which implies that PSS chains form a swollen layer on PDDA surface. The subsequently introduced PDDA chains penetrate into such a swollen layer and form complexes with PSS chains. This is quite different from that for the nonlinear 

Indeed, PEMs not only can be fabricated in water but also can be constructed in organic solvents and water-organic solvent mixtures [22]. Organic solvents and water-organic solvent mixmres usually have a smaller dielectric constant than water. Thus, more ion pairs will be formed compared with that in aqueous solutions [47]. Besides, the solvation of ions in water-organic solvent mixtures should be different from that in water because the solvent molecules can form complexes in the mixmres [48]. Therefore, it is expected that the specific ion effect in organic 

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