Studies Of Spin Diffusion By Using Dipolar Filter

In this dissertation, the methods of dipolar filter were employed to study the spin diffusion of polymers in the solid-state high-resolution NMR spectroscopy. Not only the multiphase polymers but also homogeneous amorphous polymers were our research objects. In our research, we also used some basic methods, such as: cross-polarization (CP) and magic angle spinning (MAS) techniques.Starting from the phenomenological Bloembergen-Purcell-Pound equation a relation between magic-angle spinning (MAS) rate and spin diffusion is derived. The resulting model equation was fitted to observed spin diffusion versus MAS rate data obtained at 298 K on an high-density polyethylene sample, revealing a reduction in the effective spin diffusivity by (65 + 5)% when increasing the MAS rate from 2 to 12 kHz. The same model equation enabled the rigid-lattice diffusivity to be estimated and was found to be only slightly higher by approximately 10%, compared to the spin diffusivity observed at the lowest MAS rate applied (2 kHz) .Moreover, the model equation predicts a reduction in the effective spin diffusivity by more than 90% when increasing the MAS rate to more than 30 kHz.We also observed the phenomenon of dynamical heterogeneities in PVAc in the NMR experiments with using dipolar filter. Through simulating the spectra of spin diffusion, the line shape was composed of three different components (temporarily existing adscription problem). In the plot of these three components percentage V.S. spin diffusion time, an interesting inflexion appears when spin diffusion time is about 500us.