Dynamics and conformations of PEO chains chemically bonded on silica: comparison between 1H and 2H NMR.
1H NMR was used to study the motion of monomer units in a layer of poly(ethylene oxide) chains grafted on silica. First, the dependence of the relaxation times on the grafting ratios is discussed qualitatively from a phenomenological point of view. Next, the NMR line narrowing effect by high-speed rotation is observed in the same samples with different grafting ratios. The magic angle spinning technique permits determination of two correlation times for each grafting ratio: tau(c) characteristic of an environment with a fast motion and tau(l) characteristic of an environment with a slow motion. In addition, the dynamics of these grafted chains are investigated by deuterium NMR (2H NMR), which is sensitive to the anisotropy of molecular motion. The evolution has been studied for two extreme grafting ratios and each time as a function of temperature. The anisotropy is more marked at low temperatures and for a low grafting ratio. The results are consistent with the 1H NMR relaxation times measured as a function of temperature.
Tajouri
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Université de Tunis - IPEIT - UR 0113/04, 2, rue Jawhar Let Nahrou - Montfleury, 1008 Tunis, Tunisia. tahar.tajouri@ipeit.rnu.tn
Hommel
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