Technical Note pubs.acs.org/ac
Thermal Processing as a Means to Prepare Durable, Submicron Thickness Ionomer Films for Study by Transmission Infrared Spectroscopy Chang Kyu Byun,† Tifani Parker,† Chunchao Liang,† Ian Kendrick,‡ Nicholas Dimakis,§ Eugene S. Smotkin,‡ Li-Mei Jin,⊥ Dongqing Zhuang,⊥ Darryl D. DesMarteau,⊥ Stephen E. Creager,⊥ and Carol Korzeniewski*,† †
Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061, United States Department of Chemistry and Chemical Biology, Northeastern University, 360 Huntington Avenue, Boston, Massachusetts 02115, United States § Department of Physics and Geology, University of Texas Pan American, 1201 West University Drive, Edinburg, Texas 78539, United States ⊥ Department of Chemistry, Clemson University, Clemson, South Carolina 29634-0973, United States ‡
S Supporting Information *
ABSTRACT: A high temperature solution processing method was adapted to prepare durable, freestanding, submicrometer thickness films for transmission infrared spectroscopy studies of ionomer membrane. The materials retain structural integrity following cleaning and ion-exchange steps in boiling solutions, similar to a commercial fuel cell membrane. Unlike commercial membrane, which typically has thicknesses of >25 μm, the structural properties of the submicrometer thickness materials can be probed in mid-infrared spectral measurements with the use of transmission sampling. Relative to the infrared attenuated total reflection (ATR) technique, transmission measurements can sample ionomer membrane materials more uniformly and suffer less distortion from optical effects. Spectra are reported for thermally processed Nafion and related perfluoroalkyl ionomer materials containing phosphonate and phosphinate moieties substituted for the sulfonate end group on the side chain. Band assignments for complex or unexpected features are aided by density functional theory (DFT) calculations.
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Scheme 1. Protonated Forms of Perfluoroalkyl Ionomer Materials Employeda
uel cells are among the leading technologies in the effort to develop efficient, clean electrical power sources. Polymer electrolyte (or proton exchange) membrane (PEM) fuel cells have received a great deal of attention, because they are able to operate at low (
