Spin diffusion in block copolymers as studied by pulsed NMR

Correlation between 1H FID and T1rho components in heterogeneous polymer systems: an application to SBS

Wideline 1H FID and relaxation measurements of a relatively simple motionally heterogeneous system, the triblock copolymer styrene-butadiene-styrene, have been performed in a temperature range between the polystyrene and polybutadiene glass transition temperatures. The two FID and the two spin lattice relaxation time in the rotating frame (T1rho) components found at each temperature have been correlated by means of a two-dimensional approach. It is shown that this approach allows dynamic information, not accessible simply by interpreting proton T1 and T1rho data, to be revealed. In the case examined, the correlation found could be confirmed by high-resolution 1H T1rho-selective 13C Cross Polarization experiments.

Effect of solvent exchange on the solid structure and dissolution behavior of cellulose

Effects of solvent exchange and milling on the solid structure of cellulose were investigated, using small- and wide-angle X-ray scattering and solid-state NMR. The solvent exchange facilitated the dissolution of cellulose in LiCl/DMAc with no change of the crystalline structure of cellulose. In contrast, the milling never facilitated the dissolution of cellulose, though the crystalline structure was almost destroyed. These facts show that the crystalline structure of cellulose hardly affects the dissolution in LiCl/DMAc. The fractal dimensions determined by the small-angle X-ray scattering measurements were increased by the solvent exchange, suggesting that the aggregation state of the cellulose microfibril is affected. It was also suggested by the NMR (1)H spin relaxation time measurements that the solvent exchange enhances the molecular mobility of cellulose and shortens the characteristic length along the microfibril, which allows easier access of the solvent molecule to cellulose.

Proton spin diffusion for spatial heterogeneity and morphology investigations of polymers

The diffusion of Zeeman spin order in the laboratory frame for a system with microscopic spatial heterogeneity, due to either molecular mobility or chemical heterogeneity, has been analysed by solving the diffusion equation in the limit of two different models. By simulation of proton spin diffusion nuclear magnetic resonance (NMR) spectral areas for poly(ethylene oxide) we have demonstrated, for both models, the sensitivity of these observables to phase domain size and to the dimensionality of the diffusion process. The possibility to obtain information about the morphology is analysed. Results from calculations based on the two models are compared with experimental spin diffusion results from 1H NMR spectra of poly(ethylene oxide). Two methods for filtering the z-magnetization from the different phase domains in a solid are discussed. The efficiency of a magnetization dipolar filter based on magic and polarization echoes is presented.

Solid-state NMR studies of 1H spin diffusion in adsorbed organic molecules

1H spin diffusion times of toluene (MB) and tetrahydrofuran (THF) adsorbed on a series of porous solids (charcoal, SiO2 and Al2O3) were measured by a selective inversion technique. The experimental results show that they cover a wide range (from less than one millisecond to several hundreds of milliseconds). For all samples, a tri-exponential behavior was observed in the magnetization recovery processes of the negative peaks. This is attributed to the existence of the two different kinds of spin diffusion processes in addition to the T1 relaxation. One is assigned to the intermolecular spin diffusion between the surface acidic protons of the adsorbent and the organic molecules adsorbed on the solid surface, the other to the intramolecular spin diffusion of adsorbed molecules. Due to hydrogen bonding between the surface hydroxyl groups and the adsorbate, the intermolecular spin diffusion of THF adsorbed on various solids is more effective compared to that of adsorbed MB. In addition, the intermolecular 1H spin diffusion between charcoal and adsorbed THF molecules was confirmed by indirect measurement suggested by Tekely et al.

Local monitoring of proton spin diffusion in static and rotating samples via spy detection

A method is described for investigating local proton "spin diffusion" by means of a 13C spin probe. The procedure does not require spectral resolution of proton resonance lines and can be applied in the laboratory frame of reference as well as in the rotating frame. Experimental results are presented for a static single crystal of ferrocene and for a powder sample under magic-angle spinning. The spin-diffusion rate constant is found to be proportional to the spinning speed in the range from 1 to 8 kHz.