Abstract
Nanometre scale chemical heterogeneity has been revealed in a phosphosilicate gel by 31P spin exchange. Monomeric phosphorus was found near to phosphorus singly cross-linked with phosphorus. Phosphorus doubly cross-linked with phosphorus was found to be remote from both other types of phosphorus species. Radiofrequency driven magnetisation exchange through 31P–31P dipolar coupling was rather ineffective, even with recoupling times of up to 30 ms, demonstrating the weak 31P–31P dipolar coupling and the effect of residual 1H–31P dipolar coupling. Effective 31P spin exchange was possible in the laboratory frame through the 1H spin interactions, when mixing times from 100 ms to 2 s were used.
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