ISSN:
0098-1273
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Broad-line NMR measurements were made on water in cellulosic samples. The spectra for oriented rayon at 65% relative humidity and room temperature consisted of a visually apparent doublet (SD) and a narrow singlet (SN) which was shifted upfield about 7 ppm from the center of the doublet. The doublet separation varied as A(3 cos2θ - 1), where θ is the angle between the fiber axis and the magnetic field; the maximum doublet separation was 350 mG at both 15.1 and 56.4 MHz, indicating the doublet is dipolar in origin. The peak-to-peak linewidth of the narrow singlet was orientation and field dependent. The upfield shift of the narrow singlet from the doublet center was field dependent. Spectra for vacuum-treated rayon consisted of only the narrow singlet, which was orientation dependent. The doublet separation decreases with increasing moisture content and is essentially zero for oriented rayon samples at 100% relative humidity; the resulting spectra due to the collapsed doublet and SN singlet was an asymmetric line. Temperature-dependent measurements were made on oriented rayon at 65% relative humidity with the fiber axis parallel to the magnetic field; when the temperature was increased from about 0° the peak-to-peak linewidth of the doublet halves and the doublet separation decreased. As the temperature was increased from about 30 to about 65°C, a previously unobserved singlet (SE) became visible. The relative amplitudes of the three lines varied with temperature as follows: The SE singlet increased, the SD doublet decreased, and the amplitude of the SN singlet remained constant. Measurements using oriented cotton samples and randomly packed rayon samples indicated that the NMR line shape of the water spectra depends upon the physical properties of the macromolecular substrate. The doublet component of the spectra is attributed to a water species (SD) which is highly bonded to the macromolecular substrate. The SE singlet is attributed to an energetic water species (SE) which is rapidly tumbling in the macromolecular environment. The SN singlet is not due to free water.
Additional Material:
10 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1979.180170202
Permalink