Layer on membrane

There are several other methods, which can be found in the hterature, to enhance the stabihty of SLM, like reimpregnating of the support, stabihza-tion by plasma polymerization, formation of barrier layers on membrane surface, or using sandwich SLM. 

The surface nature of resultant membranes modified with CTAC/PAA and TMAC/PAA ESA multiple layers would change alternately due to the alternate deposition of CTAC or TMAC and PAA layer on the surface. In order to estimate the formation of CTAC (or TMAC) and PAA layers on P(AN-co-AA) base membrane, the increment of membrane weight due to the repeated construction of composite layer on membrane surface was measured. Herein, we listed the weight value for each deposited layer of CTAC, TMAC and PAA. Here, the value of [DL] (Deposited Layer)(mmol / g) was calculated from [DL] = Am / Fw, where Am was the corresponding weight increment of membrane induced by each deposition step and Fw were 319.5 g / mol, 109.5 g / mol and 72 g / mol for CTAC, TMAC and PAA, respectively. The obtained average value of [DL] was about 1.4 mmol / g for P(AN-co-AA)/CTAC/PAA system and 1.6 mmol / g for P(AN-co-AA)/TMAC/PAA system. 

To study the charge density of PAA layer on membrane surface, we calculated the ratio of dissociated COO group and COOH group by referring to the characteristic peaks at 1446 cm-i and 1710 cm-i, respectively, revealed by FT-IR data in Figure 2-1 and Figure 3-1. For the P(AN-co-AA)/CTAC/PAA system, the value of [COO]/[COOH] was 72% for base membrane of P(AN-co-AA), after the surface was converted with CTAC layer, the value became to be 78% and then decreased to 47 % due to the assembly of PAA layer onto membrane surface. Then, the value changed to be 83% and 49% consequently as the second circle of CTAC/PAA layers was formed onto membrane surface. 

Number of self-assembed layers on membrane surface... 

Y. Fujii, S. Tsushima, S. Hirai, Effect of micro porous layer on membrane hydration path under low humidity operation of PEMFC, ECS Trans. 25 (2009) 1783-1789. 

Apart from the blend membranes, introducing an ultrathin vanadium-resistant layer on membrane support could be another choice. For example, a positively charged polymer layer such as polyethylenimine (PEI), polypyrole and polyaniline can be deposited on the surface of a Nafion membrane to increase the ion selectivity [20-22]. Even though the modification of Nafion is an effective way to improve its selectivity, the extremely high cost of the membrane matrix still limited its further application. 

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