Radiofrequency Induced Temperature Increase as a Function of Cross Polarization Contact Time in 8CB

A.K. CHATTAH; F.M. CUCCHIETTI; M. HOLOGNE; J. RAYA; P.R. LEVSTEIN

MAGNETIC RESONANCE IN CHEMISTRY

Wiley InterScience

Año: 2002 vol. 40 p. 772 - 772

0749-1581

font face="Palatino-Bold" size="3"> In this work we analyse the non-negligible heating effect that can be produced by the radiofrequency during the contact time in Hartmann-Hahn cross polarisation experiments in liquid crystals. We perform the analysis in the nematic phase of 4-n-octyl-4´-cyanobiphenyl (8CB). The heating effect is quantified through the chemical shifts of the carbon resonances which move towards their respective positions in the isotropic phase when increasing the contact time. The calibration procedure involves an independent measurement of chemical shift dependence on externally controlled bath temperature. This variation was performed in the range between 300 and 313 K covering the smectic A and nematic mesophases. An overall heating rate of 0.16 K/ms is observed during the contact time in a cross polarisation experiment performed at radio frequency of w1/2Pi aprox 80 kHz. This rate goes to appro