Lin, Guangxin

The Application of Multiple-Quantum MAS NMR to Materials

Abstract

The thesis describes the investigation of high-resolution MQ MAS NMR in rigid spin-1/2 systems. Formerly, MQC techniques were mainly applied to systems of small molecules, the newly developed MQC technique in this thesis, the 1H-MQC-filtered-MAS-NMR method, can be well applied to study the heterogeneity of inorganic and organic materials, such as silica gel, homopolymers, copolymers and their blends. In this thesis two multiple-pulse sequences were adopted: the three-pulse and the time-reversible eight-pulse sequence. The former has the advantage that the cycle time, i.e. the excitation time can be adjusted to arbitrary values, therefore it can be used to generate 1H MQC in coupled spin-1/2 systems for a wide range of dipolar interactions, especially to pump 1H MQC from a rigid system, such as the crystalline phase of polymers. But it has disadvantages: it is sensitive to chemical shifts and resonance offsets, and has low efficiency in exciting higher order coherences. The latter has higher efficiency in exciting higher order coherences and is not sensitive to chemical shifts and resonance offsets, but it has a long cycle time, so it is only effective when the dipolar interactions are not strong such as in the amorphous phase of polymers