Characterization of Heterogeneous Solvent Diffusion Environments in Anion Exchange Membranes

Abstract

1H high resolution magic angle spinning (HRMAS) NMR spectroscopy was used to characterize the solvent environments in a series of poly(phenylene)- and poly(phenylene alkylene)-based anion exchange membranes (AEMs). Multiple water and methanol environments were resolved in the membranes under HRMAS NMR. This allowed the self-diffusion rate constants to be evaluated for each different solvent environment as a function of the membrane identity, ion exchange capacity, water content, and sample temperature. These ionomers have been designed to function as binders within the catalyst layers of direct methanol fuel cells. In such applications, it is desirable to maximize the diffusion of the fuel (methanol) as well as the solvated ions to increase power output. To that end, the flexibilities of the backbone and the cationic side chains have been varied with the expectation that greater polymer mobility will lead to improved permeability. For the two types of AEMs investigated, it was observed that the methanol self-diffusion rates were preferentially reduced with respect to the water diffusion rates. It was also shown that the water diffusion rates within the AEMs were the largest at high water concentration, as observed in membranes containing the hexamethylene chain spacer in both the polymer backbone and the trimethylammonium (TMA+) cation-containing side chains.

On the parallelism between the mechanisms behind chromatography and drug delivery: the role of interactions with a stationary phase

“…This well known technique is very reliable for liquid solutions, on the contrary 1 H NMR spectrum of hydrogels is characterized by broad signals due to the residual solid-state effects related to the dipole-dipole coupling. This limitation makes the NMR spectra acquired by conventional liquid state probe heads completely useless for the structural and dynamical characterization of the materials 54 and in this direction the use of HR-MAS allowed us to overcome this limitation 39,59 .…”

“…The chosen hydrogel, specifically developed for central nervous system repair strategies, was obtained by synthesis from statistical block polycondensation between agarose and carbomer 974P (briefly termed as AC, acronymic of their main components), together with cross-linkers 36,37 . IP self-diffusion coefficients were measured in water and in gel by means of pulsed magnetic field gradients spin-echo (PGSE) nuclear magnetic resonance (NMR) spectroscopy using the high resolution magic angle spinning (HR-MAS) technique [38][39][40] . In addition we considered here also the aggregation contribution (drug-drug interaction) that takes place in water and in hydrogel and it is very common in several commonlyused drugs 41,42 .…”

The Role of Drug–Drug Interactions in Hydrogel Delivery Systems: Experimental and Model Study

“…SF self-diffusion coefficients were measured in water andi ng el by means of pulsed magnetic field gradients spin-echo (PGSE) nuclear magnetic resonance (NMR) spectroscopyu sing the high-resolution magic angle spinning (HR-MAS) technique. [28][29][30] Then, to understand the differences in terms of drug transport through water solutiona nd hydrogel environment, we propose am athematical model based on adsorptionm echanismsf irstly applied by Carta and Schirmer on polysaccharide-based hydrogels for chromatography [31] and then optimized by our research group for hydrogel-based drug-delivery systems. [32] In addition, we considered the aggregation contribution, which takes place in ad ifferent manner between the two environments and is common in several commonly-used drugs.…”

A Direct Methanol Alkaline Fuel Cell Based on Poly(phenylene) Anion Exchange Membranes

“…The synthesis of TMAC6PPC6 has been described elsewhere. 30 It is designed to be chemically compatible with TMAC6PP while allowing for greater transport of water and methanol within the electrodes. Because it is designed to transport methanol easily, TMAC6PPC6 is obviously not used as a membrane to avoid problems with methanol crossover.…”