Seyyie-i tesamüh

Nabizade Nazım'ın Servet-i Fünun'da tefrika edilen Seyyie-i Tesamüh adlı roman

NMR investigations of polymer dynamics in a partially filled porous matrix

The interior surface of well-defined porous alumina membranes (Anopore) of 20nm and 200nm pore diameter, respectively, was coated with polymer layers generated from solution by the solvent evaporation method. Deposits of poly(dimethyl siloxane) (PDMS) with nominal thicknesses ranging from 0.15 to 4.5nm --corresponding to submonolayer to multilayer films-- were investigated, and were compared to poly(butadiene) (PB) as an example for non-wetting polymers. Molecular weights below and above the critical value were studied since the bulk dynamics of such polymers are known to be qualitatively different. First results of NMR relaxation dispersion experiments on these systems are presented, supplemented by transverse relaxation times and double-quantum measurements obtained from high-field NMR. A systematic decrease of relaxation times at low fields with decreasing polymer amount is found for PDMS, but molecules retain a high degree of mobility irrespective of molecular weight. The relaxation dispersion results are supported by T2 data and 1H residual dipolar coupling (RDC) constants, and are discussed in terms of molecular order and reorientational dynamics

NMR investigations of acid doped polybenzimidazole, an electrolyte membrane for fuel cells

Fuel cells (FCs) are devices that convert the chemical energy of their reagents into electrical energy without resorting to a thermal Carnot cycle. Polymer electrolyte membrane FCs (PEMFCs) have raised considerable interest for their high energy conversion efficiency, high power density, ease of assembly, silent operation, and good environmental compatibility. Fuel cells consist mainly of an anode, a cathode and a membrane acting as electrolyte and which allows charges to selectively move between anode and cathode. Acid doped polybenzimidazole (PBI) polymers have become a very promising system for use as membranes in high temperature PEMFCs. The conductivity in FCs is well known to be directly related to the mobility of the ions through the membrane, which might involve a multi-step proton hopping process (Grotthuss mechanism) or the bulk mobility of a proton carrier. We report investigations of poly(2,5-benzimidazole) (AB-PBI) doped with phosphoric acid (PA) with different methods of NMR [1]. We have characterized the molecular interactions between the polymer matrix and the acid dopant. Heteronuclear correlation experiments were used to study hydrogen bonding characteristics. We have further studied the dynamics and order in the system at different doping levels and temperatures using 2H-NMR and 1H-Double-quantum spectroscopy. This information is of fundamental importance in order to elucidate the role of phosphoric acid in the conductivity mechanism of polybenzimidazole [2, 3]. [1] F. Conti, S. Willbold, C. Korte, W. Lehnert, D. Stolten, S. Mammi, Chem. Commun. 2012, submitted. [2] C. E. Hughes, S. Haufe, B. Angerstein, R. Kalim, U. M\ue4hr, A. Reiche, M. Baldus, J. Phys. Chem. B., 2004, 108, 13626-13631. [3] S. Suarez, S. Greenbaum, The Chemical Record, 2010, 10, 377-393