Spatially Resolved Crystalline and Amorphous Components of Polymeric Materials by Carbon-13 Chemical Shift Imaging Performed with Radio-Frequency Field Gradients

Abstract

It is shown that chemical shift imaging can be easily adapted to high-resolution solid-state experiments by means of radio-frequency field gradient technology. (The gradient is delivered by a two-turn flat coil, the axis of which coinciding with the rotor axis.) The resulting two-dimensional diagram involves chemical shift information in one dimension and spatial information (along the rotation axis) in the other dimension. Different procedures (physical filters) have been considered in order to enhance specific properties of the crystalline and amorphous components in high-density polyethylene (hdpe). Two of them rely on differences in cross-polarization or in cross-polarization inversion processes, while a third one is based on carbon-13 longitudinal relaxation times. The latter is shown to be especially efficient for effectively obtaining separate images of the amorphous and crystalline components and ultimately unraveling their distribution within the sample. In particular, it is demonstrated that two structurally distinct amorphous phases are spatially separated in the sample under investigation.