1H NMR Imaging of Residual Dipolar Couplings in Cross-Linked Elastomers: Dipolar-Encoded Longitudinal Magnetization, Double-Quantum, and Triple-Quantum Filters

Double-Quantum-Filtered NMR Signals in Inhomogeneous Magnetic Fields

“…This shows that the approximation involved in deriving Eq. [6] is valid. Finally, the normalized DQ-filtered signal is given by [7] i.e., the signal represents a DQ decay curve starting from an initial time τ = 0, after DQ coherence pumping for a duration τ .…”

“…The method of the DQ decay curves can be also applied in the case of experiments done in homogeneous magnetic fields or under magic-angle sample spinning for measuring chemically site selective dynamic order parameters (3). Moreover, this procedure can be used for 1 H NMR contrast filters to record parameter images of residual dipolar couplings in elastomers having better spatial resolution compared with that based on DQ buildup coherences (5,6).…”

“…It was shown that these couplings can be correlated with the cross-link density (3,4) and the space distribution of strain (5). Parameter images can be recorded employing 1 H DQ and TQ coherence filters in heterogeneous elastomers (5,6). Moreover, 2 H DQ-filtered NMR signals of deuterated poly(butadiene) oligomers incorporated into elastic rubber bands were used to generate contrast in 2 H NMR images of local strain in stretched elastomers (7,8).…”

“…Therefore, a detailed analysis of the spin system response to various pulse sequences is necessary in order to assess the measured NMR parameters (12). Furthermore, the possibility of recording 1 H MQ-filtered NMR signals in these inhomogeneous fields has to be investigated in connection with the successful application of this method to elastomers (3)(4)(5)(6) and biological tissues (9,10).…”

Sideband Patterns from Rotor-Encoded Longitudinal Magnetization in MAS Recoupling Experiments

“…The phase cycles of double-quantum experiments were always designed to cancel out contributions from longitudinal magnetization during t 1 . Recently, a multiple-quantum-like pulse sequence was used to monitor the decrease in the amount of longitudinal magnetization as a function of the duration of the multiple-quantum excitation and reconversion periods (18). However, this filter experiment was carried out under static conditions to measure residual couplings in elastomers and, by definition, does not involve rotor encoding.…”