ORIENTATIONAL ALIGNMENT IN SOLIDS FROM BIDIMENSIONAL ISOTROPIC-ANISOTROPIC NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY - APPLICATIONS TO THE ANALYSIS OF ARAMIDE FIBERS
Jr. Sachleben et L. Frydman, ORIENTATIONAL ALIGNMENT IN SOLIDS FROM BIDIMENSIONAL ISOTROPIC-ANISOTROPIC NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY - APPLICATIONS TO THE ANALYSIS OF ARAMIDE FIBERS, Solid state nuclear magnetic resonance, 7(4), 1997, pp. 301-311
The use of two-dimensional isotropic-anisotropic correlation spectrosc
opy for the analysis of orientational alignment in solids is presented
. The theoretical background and advantages of this natural-abundance
C-13 NMR method of measurement are discussed, and demonstrated with a
series of powder and single-crystal variable-angle correlation spectro
scopy (VACSY) experiments on model systems. The technique is subsequen
tly employed to analyze the orientational distributions of three polym
er fibers: Kevlar(R) 29, Kevlar(R) 49 and Kevlar(R) 149. Using complem
entary two-dimensional NMR data recorded on synthetic samples of poly(
p-phenyleneterephthalamide), the precursor of Kevlar(R), it was found
that these commercial fibers possess molecules distributed over a ver
y narrow orientational range with respect to the macroscopic director.
The widths measured for these director distribution arrangements were
(12+/-1.5)degrees for Kevlar(R) 29, (15+/-1.5)degrees for Kevlar(R) 4
9, and (8+/-1.5)degrees for Kevlar(R) 149. These figures compare well
with previous results obtained for non-commercial fiber samples derive
d from the same polymer. (C) 1997 Elsevier Science B.V.