Composite membranes fillers

A. S. Arico, V. Baglio, V. Di Blasio, A. Di Blasi, E. Modica, P.L. Antonucci and V. Antonucci. Surface properties of inorganic fillers for application in composite membranes-direct methanol fuel cells. Journal of Power Sources 128, 113-118 2004. 

Water Uptake of Composite Membranes Recast Nafion-based samples with and without fillers absorb more water compared to the commercial Nafion 117,115, and 112 membranes. It is observed that the water content rises slightly with the thickness of the membranes investigated. Nafion 112 indicates unexpectedly low water content in the swollen state. It is noted that even after many repetitive... 

P. Creti, P. L. Antonucci, V. Antonucci, Influence of the acid-base characteristics of inorganic fillers on the high temperature performance of composite membranes in direct methanol fuel cells. Solid State Ionics 161 (2003) 251-265. 

The most studied Nafion composite membranes with organic fillers include blends of Nafion with polypyrrole, polybenzimidazole, poly(vinyl alcohol), polyvinylidene fluoride, polyanfline, sulftmated poly(ether ether ketone), and poly(tetrafluoroethylene). 

Most of the reported inorganic fillers used to modify Nafion are composite where the inorganic particles (usually nanoparticles) are located in the membrane bulk. Most of them are prepared using the recast method, where the filler nanoparticles dispersed in a solvent are mixed with Nafion ionomer dispersion in the same solvent or a compatible one. The solution is cast on a Petri dish or a plane surface at high temperature to form the recast composite membrane. An alternative method adopted to prepare Nafion composites with silica [31, 32, 41, 95], functionalized silica [35], and zirconium and titanium phosphate [41], is the in situ sol-gel reaction method, schematized in Fig. 6.5. 

Other reported method to prepare inorganic/Nafion composite membranes is the colloidal [56] or ionic impregnation [75-78, 87, 93], where the inorganic filler is introduced a colloidal dispersion into the membrane or by exchange of by the salt cation, like Zr" ", followed by salt precipitation with the corresponding acid. 

In summary, there is a lack of information on the separate uptake of methanol and water in Nafion composite membranes which preclude any conclusion about the partition of methanol, while the effect of the filler on the liquid sorption, as noted in the case of the uptake of pure methanol (Sect. 6.5.1), seems to be complex and not easy to assess. 

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. 

Jin Y, Qiao S, Zhang ZP, Xu ZP, Smart S, Diniz da Costa JC, Lu GQ (2008) Novel Nafion composite membranes with mesoporous silica nanospheres as inorganic fillers. J Power... 

Casciola M, Bagnasco G, Domiadio A, Micoli L, Pica M, Sganappa M, Turco M (2009) Conductivity and methanol permeability of Nafion-zirconium phosphate composite membranes containing high aspect ratio filler particles. Fuel Cells 9 394-400... 

Filling the pores of a track-etched membrane with a polyelectrolyte results in a new class of polymer composite membrane, where the filler can enhance or regulate transport in the desired direetion and the traek-etched membrane can provide meehanieal stability and durabihty. Compared to dense membranes, these eomposite membranes can be tailored by the type of filler, pore size and porosity of the membrane to provide tunable transport properties. 

Vankelecom et al. (1997a) studied three types of hydrophobic porous fillers (carbon blacks, in situ methylated silicas, and silylated silicas) incorporated in PDMS membranes in order to find out under which conditions these membranes were advantageous for PV of aqueous solutions. The properties of these fillers were changed systematically in order to maximize the fluxes and selectivities of the PV of aqueous EtOH, tert-hutyl alcohol (TEA), or aroma solution. The effect of incorporation of carbon black in PDMS for the PV of a 6 wt% alcohol solution in water is based on the level of the PDMS. When using PDMS membranes filled with hydrophobic silicas, the best results were obtained with silylated silicas. Vankelecom et al. (1997b) investigated the PV of aroma compounds using zeolite-filled PDMS composite membranes. Zeolite-filled PDMS membranes were supported on the PAN asymmetric membrane coated on a nonwoven polyester. Table 9.6 shows the influence of the filler on the fluxes and overall enrichment factors. 

Another important feature of the composite membranes is that their improved mechanical properties are not affected by a decrease in conductivity, provided that the particle size of the filler is maintained sufficiently small (i.e. of the order of 1 pm). Figure 6.19 compares the conductivity of composite PEO-LiX membranes with that of a pure PEO-LiX one [39]. In the temperature range above the transition, and in particular around 100°C,... 

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