In this study, the transport properties of poly(styrene-isobutylene-styrene) (SIBS) were determined as a function of sulfonation level (0-94.9%) and counter-ion substitution (Ba þ2 , Ca þ2 , Mg þ2 , Mn þ2 , Cu þ2 , K þ1 ) for fuel cell applications. Increasing the sulfonation level improved the ion exchange capacity (IEC) of the membranes up a maximum (1.71 mequiv/g), suggesting a complex three-dimensional network at high sulfonation levels. Results show that proton conductivity increases with IEC and is very sensitive to hydration levels. 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 counter-ion studied, while proton conductivity is more sensitive to water content, which is also reduced upon the incorporation of counter-ions. To complement the studies, selectivity (i.e., proton conductivity/methanol permeability) of the studied membranes was determined and compared to NafionV R 117.
In this study, multilayered films of polyethylenimine/poly (sodium-p-styrene sulfonate) (PEI)/(PSS) and type I collagen/heparin sodium (COL)/(HEP) were fabricated using the layer-by-layer technique, and fully characterized using Infrared Variable Angle Spectroscopic Ellipsometry (IRVASE) to simultaneously analyze the chemistry, thickness, and roughness of the multilayers with respect to changes in pH of the washing solution, and changes in temperature. Film topography and Young’s modulus were obtained by atomic force microscopy (AFM) and nanoindentation. Our results show that with IRVASE it is possible to analyze the thickness of the multilayers prepared using a washing solution of pH 5, obtaining values of 71.7 nm and 40.3 nm for three bilayers of PEI/PSS and COL/HEP, respectively. Film roughness varies between multilayer systems, obtaining values of 37.76 nm for three bilayers of PEI/PSS and 33.58 nm for three bilayers of COL/HEP. Increasing the pH of the washing solution for PEI/PSS yielded thinner films that were less susceptible to thermal induced changes in film chemistry in the range of 25 – 150 °C. PEI/PSS films decreased in thickness with increasing temperature up to 75 °C, whereas above 75 °C film thickness increased. Through IRVASE, a transition temperature for the PEI/PSS multilayers was observed at 75 °C. Temperatures above 37 °C drastically alter the chemistry and the thickness of the COL/HEP multilayers indicating a possible degradation of the polymers. We obtained, through nanoindentation, a Young’s modulus of 15000 kPa and 9000 kPa for 12 bilayers of PEI/PSS and COL/HEP, respectively. These results demonstrate that, using IRVASE, we can simultaneously evaluate the physical, chemical, and thermal properties of synthetic and natural multilayered polymeric films.
The first example of a phase-transfer-catalyzed reaction carried
out in a supercritical fluid (SCF)
is reported. The kinetics of the nucleophilic displacement of
benzyl chloride with a bromide ion
in SCF solvent CO2 in the presence of acetone cosolvent is
presented. In addition, the solubility
of tetraheptylammonium bromide (THAB) in SCF CO2 in the
presence of acetone cosolvent is
reported. The reaction rate was measured at 50 and 75 °C at
pressures to 200 bar; the reaction
was found to follow first-order, reversible kinetics for the reactions
catalyzed by THAB and
zero-order kinetics for reactions catalyzed by 18-crown-6.
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