Methanol Aqueous Mixtures Research Articles

Spectroscopic and thermal characterization of the swelling behavior of nafion membranes in mixtures of water and methanol

AbstractThe spectroscopic and thermal properties of swollen Nafion membranes in methanol aqueous mixtures were investigated to understand the behavior of commercial electrolytes in the presence of polar solvents. Several differences were observed in the absorption processes depending on the composition of the solvent. Deconvolution methods were applied to study specific contributions of solvents and polymer groups based on Fourier transform infrared spectroscopy and thermogravimetric analysis. The results evidence compositional effects on the interactions between solvents and Nafion. A major influence of the nonpolar domains (hydrophobic regions) in the absorption of methanol together with a reduction of the interactions with sulfonate groups was observed. Such changes are accompanied by a modification of the cluster morphology of the equilibrated membranes evaluated by differential scanning calorimetry. These findings can be useful to improve the knowledge on Nafion's microstructure in the presence of polar solvents. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Microscopic observation of ordered colloids in sedimentation equilibrium and the importance of the Debye-screening length. 9. Compressed crystals of giant colloidal spheres (diam. 2?66 ?m)

Compressed crystal-like structures of very large polystyrene spheres (specific gravity=1.05, diameter=2–66 μm) are observed directly by a metallurgical microscope in sedimentation equilibrium and in deionized aquueous and 20 vol % methanol aqueous suspensions. Spheres of 2–42 μm in diameter float above the cover glass apart from each other. The center-to-center intersphere distance decreases as the initial concentration of spheres increases, from which Young's elastic moduli (G) for the crystal-like structures are estimated to be between 1 to 10 dyn/cm2, irrespective of the spheres size.G's in aqueous suspension are smaller than those in methanol aqueous mixtures. The crystal-like structures are compressed substantially by the gravitational field. These results are consistent with the significant role of the electrical double layers under the influence of purely electrostatic repulsive forces in the effective hard-sphere model.