Avilés-Barreto, Sonia L.

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    Functionalization and characterization of Sulfonated Poly (Styrene-Isobutylene-Styrene) membranes for fuel cells and specialty separation applications
    (2014) Avilés-Barreto, Sonia L.; Suleiman-Rosado, David; College of Engineering; Curet-Arana, María C.; Padovani, Agnes; Estévez De Vidts, Antonio L.; Department of Chemical Engineering; Coutin Rodicio, Sandra
    In this study, the transport properties of poly(styrene-isobutylene-styrene) (SIBS) block copolymer were determined as a function of sulfonation level (0-94.9 %), counter ion substitution (Ba+2, Ca+2, Mg+2, Mn+2, Cu+2, K+1), single-walled carbon nanotubes (SWCNTs) functionalization (carboxylic groups, aminomethanesulfonic acid and p-aminobenzoic acid), SWCNT loading (0.01, 0.1 and 1.0 wt.%), and blends with radial poly(styrene-isoprene) for direct methanol fuel cell (DMFC) and chemical and biological protective clothing (CBPC) applications. Increasing the sulfonation level improved the ion exchange capacity (IEC) of the membranes up a maximum, suggesting a complex 3-D network at high sulfonation levels. Results show that proton conductivity increases with IEC and is quite sensitive to hydration levels and the type of water (i.e., bound or bulk) inside these proton exchange membranes (PEM). Methanol permeability, although also sensitive to IEC, shows a different behavior than proton conductivity suggesting fundamental differences in their transport mechanism. The incorporation of counter ion substitution decreases both methanol and proton transport. Methanol permeability seems to be related to the size of the studied counter ions, while proton conductivity is more sensitive to water content, which is also reduced upon the incorporation of counter ions. Methanol permeability is sensitive to SWCNTs addition, since its transport mechanism seems to be controlled by their presence and loading. The addition of radial poly(styreneisoprene) creates unique morphologies that lead to high water uptake, poor interconnectivity of sulfonic groups and low methanol permeability. Selectivity (i.e., proton conductivity/methanol permeability) of the studied membranes was determined and compared to Nafion® 117 to complement the studies. Values suggest an optimum SWCNT loading (0.1 wt.%) for the highest sulfonation level studied with this functionalization (SIBS 89.7). Additionally, the SWCNT functionalization with sulfonic groups improves the transport properties of the sulfonated PEM. The efficiency of the membranes to separate dimethyl methylphosphonate (DMMP), the simulant of the chemical warfare agent Sarin, and water vapor also shows high values for the sulfonated and nanocomposite membranes. Vapor permeability studies suggest that the combination of ionic domains with unique morphological arrangements can lead to high separation efficiencies for CBPC application.