روزنامه با شماره پیاپی سال 2003

7

205

211

The diblock copolymer containing 43.5 wt.% of polystyrene (PS) (Mw=15 000) and polyoxyethylene (POE) (Mw=19 500) was investigated by integral and by partial thermally stimulated depolarization current (TSDC) measurements in the temperature range of 173–293 K. The first peak P1, widely distributed from 183 to 213 K, was a dipolar peak attributed to the initial stage of glass transition in POE. The second peak P2, with a maximum at 273 K, was due to glass transition. The third peak P3, with a maximum at about 263 K, was caused by the space charge relaxation localized at the interfaces between the ordered and nonordered phases in POE, Maxwell–Wagner relaxation, representing a precursor in melting of POE crystals. The results were supported by determination of activation energy Ea of the partial peaks, which covered the whole range of investigation, and by differential scanning calorimetry (DSC) measurements. The Ea(T) distribution showed a maximum in entropy change at 219±4 K. Some runs with samples containing different amounts of the PS component were considered. All the relaxations were coming from the POE block. The current due to PS slightly overlapped the total spectra without interaction. The influence of the repeated runs was observed and discussed.

Food Microbiology

2003

Food Microbiology