Breakdown in the efficiency factor of the mixed Magic Sandwich Echo: A novel NMR probe for slow motions

A novel NMR approach to obtain insights on slow dynamics in glasses is described. The suggested approach is based on the efficiency in refocusing the proton dipolar FID by using Magic Sandwich Echo sequence, which appears strongly influenced by the orientational time autocorrelation function of the internuclear vector. The analysis of the phenomenon is performed with the aid of computer simulations and phenomenological models. The technique is applied to the alpha-relaxation process in a co-polymeric rubber and it is argued to be useful in a variety of NMR studies in glasses, polymers and possibly solids. (C) 2011 Elsevier B.V. All rights reserved.