Influence of the cross-link density and the filler content on segment dynamics in dry and swollen natural rubber studied by the NMR dipolar-correlation effect
| Autor: | Farida Grinberg, Winfried Kuhn, Maciej Garbarczyk |
|---|---|
| Rok vydání: | 1999 |
| Předmět: |
Chemistry
Attenuation Physics::Medical Physics General Physics and Astronomy Pulse sequence Molecular physics Dipole Nuclear magnetic resonance Amplitude Natural rubber visual_art visual_art.visual_art_medium Physical and Theoretical Chemistry skin and connective tissue diseases Quotient Magnetic dipole–dipole interaction Spin-½ |
| Zdroj: | The Journal of Chemical Physics. 111:11222-11231 |
| ISSN: | 1089-7690 0021-9606 |
| DOI: | 10.1063/1.480478 |
| Popis: | Chain dynamics in a series of natural rubbers with different cross-link densities was studied using the dipolar correlation effect (DCE) on the stimulated echo. In dry samples, amplitudes of the stimulated echo were shown to be affected by attenuation mechanisms due to the DCE and spin exchange which occurs between the protons of CH and CH3 (and/or CH2) groups of polyisoprene chains. The estimated spin exchange time was 0.04 s. The DCE free of undulations due to spin exchange was examined using a special modification of the radio frequency pulse sequence with additional π-pulses inserted in the free-evolution intervals. Modulations of stimulated echo amplitudes could completely be suppressed. A strong dependence of the DCE on the cross-link density was observed. Attenuation curves of the dipolar-correlation quotient, that is, the quotient of the stimulated and the primary echo amplitudes, were fitted using analytical expressions. The mean-squared fluctuation of the dipolar coupling constant, 〈δΩd2〉, and c... |
| Databáze: | OpenAIRE |
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