Orientational alignment in solids from bidimensional isotropic-anisotropic nuclear magnetic resonance spectroscopy: applications to the analysis of aramide fibers
✍ Scribed by Joseph R. Sachleben; Lucio Frydman
- Book ID
- 104357822
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 969 KB
- Volume
- 7
- Category
- Article
- ISSN
- 0926-2040
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✦ Synopsis
The use of two-dimensional isotropic-anisotropic correlation spectroscopy for the analysis of orientational alignment in solids is presented. The theoretical background and advantages of this natural-abundance "C NMR method of measurement are discussed, and demonstrated with a series of powder and single-crystal variable-angle correlation spectroscopy (VACSY) experiments on model systems. The technique is subsequently employed to analyze the orientational distributions of three polymer fibers: Kevlar @ 29 Kevlar@ 49 and Kevlar@ 149. Using complementary two-dimensional NMR data recorded on , synthetic samples of poly( p-phenyleneterephthalamide), the precursor of Kevlar @, it was found that these commercial fibers possess molecules distributed over a very narrow orientational range with respect to the macroscopic director. The widths measured for these director distribution arrangements were (12 + 1.5)" for Kevlar@ 29, (15 + 1.5)" for Kevlar @ 49, and (8 f 1.5)" for Kevlar@ 149. These figures compare well with previous results obtained for non-commercial fiber samples derived from the same polymer. 0 1997 Elsevier Science B.V.