ISSN:
0887-6266
Keywords:
carbon dioxide
;
spin relaxation
;
polyisobutylene
;
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Recently we presented the dynamics of 13CO2 molecules sorbed in silicone rubber (PDMS) ascertained from spin relaxation experiments. Results of a similar investigation for 13CO2 sorbed in polyisobutene (PIB) are presented in this report. The spin-lattice and spin-spin relaxation times as well as nuclear Overhauser enhancements (NOE) were determined as a function of temperature and Larmor frequency. The relaxation mechanisms found to be important for 13CO2/PIB system are intermolecular dipole-dipole relaxation and chemical shift anisotropy with a minor contribution from spin rotation relaxation. We have determined the parameters which characterize correlation times for 13CO2 collisional motion, rotational motion, and translational motions in the PIB. The self-diffusion coefficient of 5.15 × 10-8 cm2/s obtained from the nuclear magnetic resonance (NMR) data is close to the literature value of the mutual diffusion coefficient of CO2 in PIB at 300 K obtained from permeability measurements. In contrast to the case of CO2/PDMS in which a broad distribution (characterized by a fractional exponential correlation function of the Williams-Watts type with α = 0.58) is observed, a sharp distribution with a fractional exponent, α, of 0.99 is found for the CO2/PIB system. Instead of assuming an Arrhenius type temperature dependence, we used a Williams-Landel-Ferry type temperature dependence and found it to be better suited to describe the behavior of this system. PIB is a densely packed “strong” chain polymer which responds gradually to the temperature variation and gas sorption. In contrast PDMS is a relatively loosely packed “fragile” polymer with a propensity to exhibit rapid dynamic responses to the temperature change and gas sorption. © 1993 John Wiley & Sons, Inc.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/polb.1993.090310916
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