A spinning thermometer to monitor microwave heating and glass transitions in dynamic nuclear polarization

作者：Mieville Pascal^*; Vitzthum Veronika; Caporini Marc A; Jannin Sami; Gerber Lemaire Sandrine; Bodenhausen Geoffrey

来源：Magnetic Resonance in Chemistry, 2011, 49(11): 689-692.

DOI：10.1002/mrc.2811

• dynamic nuclear polarization
• magic angle spinning (MAS)
• MAS thermometry
• potassium bromide (KBr)
• glass transition

As previously demonstrated by Thurber and Tycko, the peak position of (79)Br in potassium bromide (KBr) allows one to determine the temperature of a spinning sample. We propose to adapt the original design by using a compact KBr tablet placed at the bottom of the magic angle spinning rotor, separated from the sample under investigation by a thin disk made of polytetrafluoroethylene (or 'Teflon'(R)). This design allows spinning the sample up to at least 16 kHz. The KBr tablet can remain in the rotor when changing the sample under investigation. Calibration in the range of 98 < T < 320 K has been carried out in a static rotor by inserting a platinum thermometer. The accuracy is better than +/- 0.9 K, even in the presence of microwave irradiation. Irradiation with 5W microwaves at 263 GHz leads to a small temperature increase of 3.6 +/- 1.4 K in either static or spinning samples. The dynamic nuclear polarization enhancement decreases with increasing temperature, in particular when a frozen glassy sample undergoes a glass transition.

• 出版日期2011-11