Heating liquid dielectrics by time dependent fields |
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Authors: | A Khalife U Pathak R Richert |
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Institution: | 1.Department of Chemistry and Biochemistry,Arizona State University,Tempe,USA |
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Abstract: | Steady state and time-resolved dielectric relaxation experiments are performed at high
fields on viscous glycerol and the effects of energy absorption from the electric field
are studied. Time resolution is obtained by a sinusoidal field whose amplitude is switched
from a low to a high level and by recording voltage and current traces with an
oscilloscope during this transition. Based on their distinct time and frequency
dependences, three sources of modifying the dynamics and dielectric loss via an increase
in the effective temperature can be distinguished: electrode temperature, real sample
temperature, and configurational temperatures of the modes that absorbed the energy.
Isothermal conditions that are desired for focusing on the configurational temperature
changes (as in dielectric hole burning and related techniques) are maintained only for
very thin samples and for moderate power levels. For high frequencies, say
ν > 1 MHz, changes of the real temperature will
exceed the effects of configurational temperatures in the case of macroscopic samples.
Regarding microwave chemistry, heating via cell phone use, and related situations in which
materials are subject to fields involving frequencies beyond the MHz regime, we conclude
that changes in the configurational (or fictive) temperatures remain negligible compared
with the increase of the real temperature. This simplifies the assessment of how time
dependent electric fields modify the properties of materials. |
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