Membranes impregnation blending

There are several approaches to the preparation of multicomponent materials, and the method utilized depends largely on the nature of the conductor used. In the case of polyacetylene blends, in situ polymerization of acetylene into a polymeric matrix has been a successful technique. A film of the matrix polymer is initially swelled in a solution of a typical Ziegler-Natta type initiator and, after washing, the impregnated swollen matrix is exposed to acetylene gas. Polymerization occurs as acetylene diffuses into the membrane. The composite material is then oxidatively doped to form a conductor. Low density polyethylene (136,137) and polybutadiene (138) have both been used in this manner. 

Dubey, V., Pandey, L. K., and Saxena, C. (2005). Pervaporative separation of ethanol/water azeotrope using a novel chitosan-impregnated bacterial cellulose membrane and chitosan-poly(vinyl alcohol) blends. I. Membr. ScL 251,131-136. 

Blending Nafion polymer with other polymeric materials has also been tried by some researchers, hi one such study, poly(l-methylpyrrole) has been impregnated with commercial Nafion membrane by in situ polymerization. A decrease of more than 90% in the permeability of the membranes to methanol is reported, although the ionic resistance of such heavily loaded membranes became too high for high-power fuel cells. At lower poly(l-methylpyrrole) loadings, a decrease in methanol permeability by as much as 50% could be realized without a significant increase in ionic... 

Hydrophilic polymers such as poly (vinyl alcohol) or polyoxyethylene can be impregnated with a mineral acid and behave as solid proton conductors [119]. Several researchers [120] showed that polyethylenimine-sulfuric acid and phosphoric acid systems were well-behaved solid proton conductors under anhydrous conditions. Further information regarding these membranes is available in the literature [120]. Finally, Cakmak and Bicaksi [121] satisfactorily elaborated PEEK/PEI blend films. 

As a substimte to Nafion impregnation into a fluoropolymer matrix, solution cast films have been prepared from blends of Nafion and vinylidene fluoride-hex-afluoropropylene copolymer [16]. Upon addition of 20 60% vinylidene copolymer, a steep decrease in proton conductivity was observed, from 10 " S cm to 10 -10 S cm , which was accompanied by a significant decrease in methanol permeability. In a more recent paper [27], Si et al. solution cast membranes composed of Nafion and poly(vinylidene fluoride), henceforth denoted as PVDF, where characterized where the PVDF content was varied from 0 to 65 wt%. As expected, the conductivity and methanol permeability decreased with inaeasing PVDF content, with a much more dramatic drop in transport parameters when the PVDF content was >50%. From proton conductivity and methanol permeability data, the relative selectivity can be determined ... 

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