AI Article Synopsis
- The study analyzed fast dynamics in polymers at microwave frequencies (0.5 to 18 GHz) across a temperature range of 20 to 190 degrees C using high frequency dielectric spectroscopy.
- Isochronal dielectric loss data were collected to simplify the complex temperature-dependent background loss, focusing on polymers like PCL, PEO, and PLA-b-PEO-b-PLA, which have low glass transition temperatures.
- The findings showed a single broad relaxation process in certain polymers, with the behavior resembling Johari-Goldstein beta relaxation, and suggested that this relaxation is linked to local motions rather than the end groups of the polymers.
Article Abstract
Fast dynamics within the microwave frequency range (approximately gigahertz) in polymer systems as a function of temperature (in the range from 20 to 190 degrees C) were studied using high frequency dielectric spectroscopy. The frequency of radiation was varied from 0.5 to 18 GHz. The isochronal dielectric loss data were taken to eliminate the complexity arising from the frequency-independent, temperature-dependent background loss in the condensed phase. These studies were conducted for poly(caprolactone) (PCL), poly(ethylene oxide) (PEO), poly(ethylene oxide) with methoxy end group (PEO-CH3), PLA-b-PEO-b-PLA triblock copolymers, and several polymers with high glass transition temperatures. These polymers possess glass temperatures ranging from -62 degrees C (PCL) to 110 degrees C (PMMA). One broad relaxation process was found only for polymers (PCL, PEO, and PLA-b-PEO-b-PLA) with low glass transition temperatures. The effect due to end groups was investigated by comparing the results of PEO with hydroxy versus methoxy end groups. The measured relaxation process was determined not to be associated with end groups. The results from temperature-dependent dielectric spectroscopy indicate that the relaxation process follows an Arrhenius T dependence suggesting that it is due to local motions. The activation energy of the relaxation process was measured and investigated based on the coupling model. The results suggest that the observed relaxation process behaves as a Johari-Goldstein beta relaxation.
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| http://dx.doi.org/10.1063/1.2756036 | DOI Listing |
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