Inorganic fillers permeability reduction

As mentioned, inorganic fillers with high aspect ratios are expected to lead to more effective permeability reduction in membranes [19]. According to Fig. 9.2, fillers in the form of flakes would be much more effective in reducing the diffusion and therefore the permeability of membranes than spherical particles. 

Paradoxically, the efforts to reduce the methanol permeabilities of Nalion with inorganic or organic fillers in most cases yield composite membranes with permeabilities similar to that obtained by optimizing the cast procedure of pure Nafion [302]. Nevertheless, the reduction of methanol permeability by itself is not a criterion for improving DMFC performance because it is usually associated to a reduction of the proton conductivity. We will analyze this property in Sect. 6.5.5 as a previous step to discuss the behavior of the proton-conducting membranes in terms of alcohol selectivity defined by Eq. 6.2. 

A good affinity between the polymer phase and fillers can lead to a rigidified polymer region around the nanoparticles (Case 3, Fig. 7.6). The rednced mobility of the polymeric chains and the possible formation of semicrystalline domains close to the inorganic phase determine a reduction in the permeation coefficient. In this condition, the efficiency of the nanoparticles can also be threatened becanse of the reduced flux at the interface. However, the permeability decrease typically corresponds to an... 

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