Mayumi Shimomura

Broadband dielectric study of α–β separation for supercooled glycerol–water mixtures

Broadband dielectric measurements for 60, 65, 70, 80, and 100 wt% glycerol–water mixtures were performed in the frequency range of 10 μHz–30 GHz and in the temperature range of 148–298 K. In the lower temperature range, the separation of the β- and α-processes occurred for all the mixtures. The relaxation strength of the α-process below the separation temperature exhibits a maximum at a mole fraction of water, xw≅0.55, and the relaxation strength of the β-process increases with increasing xw. In our previous study, the concentration dependence of the dielectric behavior of the alcohol–water mixtures at 25 °C was interpreted using a cooperative domain (CD), in which the reorientation of molecules occurred cooperatively. The concentration dependence of the dielectric behavior for the glycerol–water mixtures is interpreted using a CD model.

Dielectric study of the α and β processes in supercooled ethylene glycol oligomer–water mixtures

Broadband dielectric measurements for 65 wt % ethylene glycol oligomer (EGO)–water mixtures with one to six repeat units of EGO molecules were performed in the frequency range of 10 μHz–10 GHz and the temperature range of 128–298 K. In the case of the water-EGO mixtures with one and two repeat units of the EGO molecule (small EGO), the shape of the dielectric loss peak of the primary process is asymmetrical about the logarithm of the frequency of maximum loss above the crossover temperature, TC. The asymmetric process continues to the α process at a low frequency, and an additional β process appears in the frequency range higher than that of the α process below TC. In contrast, the water-EGO mixtures with three or more repeat units of the EGO molecule (large EGO) show a broad and symmetrical loss peak of the primary process above TC. The symmetric process continues to the β process, and an additional α process appears in the frequency range lower than that of the β process below TC. These different scenar...

Dielectric study on α- and β-processes in supercooled diethyleneglycol– and pentaethyleneglycol–water mixtures

Abstract Broadband dielectric measurements on 65 wt% diethyleneglycol– and pentaethyleneglycol–water mixtures were performed in the frequency range of 10 μHz–10 GHz and in the temperature range of 128–273 K. The α- and β-relaxation processes observed in the lower temperature range merged in the higher temperature range. The relaxation curve for the diethyleneglycol–water mixture was asymmetric above the separation temperature, and continued to the lower frequency process below the separation temperature, and an additional relaxation process appeared at the higher frequency below the separation temperature. In contrast, the relaxation curve for the pentaethyleneglycol–water mixture is symmetric above the separation temperature. The relaxation process continued to a higher frequency process below the separation temperature, and another lower frequency relaxation process appeared. These results reflect the cooperative motion of water and solute molecules with different sizes for each mixture.

Broadband dielectric study of the glass transition in poly(ethyleneglycol)-water mixture

We performed broadband dielectric measurements of a polyethyleneglycol-water mixture in the frequency range between 10 GHz and 1 microHz and the temperature range between 300 and 133 K. One relaxation process is observed throughout the whole temperature range. The temperature dependence of the relaxation time clearly obeys the Vogel-Fulcher law above 183 K, and the Arrhenius law below 183 K. This observed relaxation process is the secondary process, and the primary process related to the glass transition is masked by the low-frequency ionic contribution below 183 K. The glass transition concerned with the masked primary process leads to the Vogel-Fulcher to Arrhenius transition of the secondary process.

Dynamics of polymer and glass transition in partially crystallized polymer solution studied by dielectric spectroscopy.

The local chain motion of poly(vinyl acetate) (PVAc) in 20 wt% PVAc benzene solution was observed by broadband dielectric spectroscopy in the frequency range of 10 μHz–10 GHz at various temperatures between −20 and +40°C from the partially crystallized state, which is composed of a crystallized benzene phase and non-crystallized PVAc/benzene solution phase, below the melting temperature, T m, of benzene to the liquid state above T m. The relaxation time of the local chain motion of PVAc shows extremely strong temperature dependence below T m. This chain motion of PVAc is the origin of the glass transition observed by differential scanning calorimetry for the partially crystallized state of the PVAc/benzene mixture below T m.

Broadband Dielectric Study on Alpha‐ and Beta‐Process for Poly(Ethylene Glycol)‐Water Mixtures

Broadband dielectric measurements of poly(ethylene glycol)(PEG)‐water mixtures with various molecular weights of PEG were carried out in the frequency range of 1μHz to 30GHz and in the temperature range of 130K to 298K. The shape of the loss peak in the liquid state at high temperature is strongly related to the types of the separation of the α and β processes in low temperature. The characteristic length of the molecular motion concerned with the relaxation processes were estimated by the PEG molecular size dependence of the relaxation time.

Concentration Dependence of the α‐ and β‐Processes for Alcohol‐Water Mixtures

We performed broadband dielectric measurements for triethylenelgycol‐water mixtures with various water contents in the frequency range between 1 μHz and 30 GHz in the temperature range between 130 K and 300 K. For the lower temperature range, the α‐ and β‐processes were observed for each mixture. The β‐process depends on the water content. The β‐process for lower water content relates to the local motion of solute molecules and for higher water content mixtures relates to the motion of the water molecules.