Browsing by Author "Jackson, A"

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    Humidity-induced phase transitions in ion-containing block copolymer membranes.
    (American Chemical Society, 2008-03-25) Park, MJ; Nedoma, AJ; Geissler, PL; Balsara, NP; Jackson, A; Cookson, DJ
    The phase behavior of ion-containing block copolymer membranes in equilibrium with humidified air is studied as a function of the relative humidity (RH) of the surrounding air, ion content of the copolymer, and temperature. Increasing RH at constant temperature results in both disorder-to-order and order-to-order transitions. In-situ small-angle neutron scattering experiments on the open block copolymer system, when combined with wafer uptake measurement, indicate that the disorder-to-order transition is driven by an increase in the partial molar entropy of the water molecules in the ordered phase relative to that in the disordered phase. This is in contrast to most systems wherein increasing entropy results in stabilization of the disordered phase. © 2008, American Chemical Society
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    Increased water retention in polymer electrolyte membranes at elevated temperatures assisted by capillary condensation
    (American Chemical Society, 2007-11) Park, MJ; Downing, KH; Jackson, A; Gomez, ED; Minor, AM; Cookson, DJ; Weber, AZ; Balsara, NP
    We establish a new systematic methodology for controlling the water retention of polymer electrolyte membranes. Block copolymer membranes comprising hydrophilic phases with widths ranging from 2 to 5 nm become wetter as the temperature of the surrounding air is increased at constant relative humidity. The widths of the moist hydrophilic phases were measured by cryogenic electron microscopy experiments performed on humid membranes. Simple calculations suggest that capillary condensation is important at these length scales. The correlation between moisture content and proton conductivity of the membranes is demonstrated. © 2007, American Chemical Society