th - 1988 - 51st ENC Conference
th - 1988 - 51st ENC Conference
th - 1988 - 51st ENC Conference
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
144 I<br />
I IH AND 13C REFOCUSED GRADIENT IMAGING OF SOLIDS<br />
J. B. Miller* and A. N. Garroway<br />
Naval Research Laboratory, Code 6120<br />
Washington, DC 20375-5000<br />
We have previously demonstrated a technique for removing<br />
distortions from NMR images due to chemical shift and susceptibility<br />
effects which we call refocused gradient imaging (RGI). The technique<br />
relies on <strong>th</strong>e Carr-Purcell pulse sequence to refocus <strong>th</strong>e chemical-<br />
shift-like evolution of <strong>th</strong>e spins. The sign of <strong>th</strong>e gradient is<br />
switched synchronously wi<strong>th</strong> <strong>th</strong>e rf pulses so <strong>th</strong>at gradient evolution<br />
is not refocused.<br />
Here we extend refocused gradient imaging to <strong>th</strong>e observation of<br />
solids. For high natural abundance spins where <strong>th</strong>e homonuclear<br />
dipole-dipole interaction dominates, <strong>th</strong>e Carr-Purcell sequence is<br />
replaced by a pulse sequence which simultaneously refocuses <strong>th</strong>e<br />
dipolar and chemical-shift-like interactions. For low natural<br />
abundance spins <strong>th</strong>e Carr-Purcell sequence is used. Where necessary,<br />
high power decoupling of heteronuclei may be added.<br />
We describe <strong>th</strong>e pulse sequences used for RGI of solids and show<br />
examples of bo<strong>th</strong> IH and 13C images. The relative merits of IH and<br />
13C RGI are discussed. We find <strong>th</strong>at because of differences in<br />
experimental parameters and more efficient line-narrowing for 13C RGI,<br />
<strong>th</strong>e low natural abundance of 13C is not a severe limitation for carbon<br />
imaging of solids.<br />
145 I<br />
DERIVATION OF POLYMER RI~IEOLOGICAL CONSTANTS<br />
FROM THE VISCOSITY AND TEMPERATURE DEPEND<strong>ENC</strong>E OF xsC NMP.<br />
RELAXATION PARAMETERS: Anita J. Brandolini, Mobil Chemical<br />
Company, Edison Laboratory, P.O. Box 240, Edison, New<br />
Jersey 08818<br />
NMR relaxation parameters characterize polymer chain<br />
motions on a local scale; <strong>th</strong>eological constants describe<br />
<strong>th</strong>e viscoelastic properties of a bulk material.<br />
CorrelatinE bulk property measurements wi<strong>th</strong> spectroscopic<br />
data enables one to determine <strong>th</strong>e contribution of local<br />
seEmental reorientations to overall chain motions. The<br />
IsC NMR llnewid<strong>th</strong>s of low molecular-weight<br />
polyisobutylenes exhibit power-law dependences on sample<br />
viscosity. The exponent, which is different for each<br />
carbon type (quaternary, me<strong>th</strong>ylene, and me<strong>th</strong>yl), specifies<br />
<strong>th</strong>e fractional contribution of each carbon type to <strong>th</strong>e<br />
polymer's free volume and monomeric friction coefficient.<br />
Fur<strong>th</strong>ermore, <strong>th</strong>e IsC NMR linewid<strong>th</strong>s have a<br />
Williams-Landel-Ferry (WLF) dependence on temperature,<br />
which is <strong>th</strong>e same form observed for <strong>th</strong>e temperature<br />
variation of many bulk viscoelastic properties. The<br />
derived values for free volume and <strong>th</strong>ermal expansion<br />
coefficient aEree wi<strong>th</strong> published rheological parameters to<br />
wi<strong>th</strong>in ±10%.<br />
171
Change language