The spin-system response to a dipolar spin coupling modulation. Theoretical description of NMR spectrum narrowing effects observed on polymer-solvent systems. Experimental illustration from polydimethylsiloxane chains

Abstract

The response of a spin system to a dipolar spin coupling modulation is quantitatively described to the second order in the spin interaction. The dependence of side band amplitudes upon the spinning frequency is given. Sample spinning effects are considered in different general cases where internal motion of nuclei, or exchange narrowing, are involved in the mechanism governing the loss of spin quantum coherence. Illustrations of some properties characterizing sample spinning effects are presented from entangled polydimethylsiloxane chains in solution and from a partly swollen polydimethylsiloxane network structure.