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  • Author or Editor: J. Moura Ramos x
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Abstract  

The relaxation of electric field-induced polar orientation in a side-chain-bearing liquid-crystalline polysiloxane was measured by means of thermally stimulated depolarization currents. Different relaxation mechanisms were identified and characterized: the glass transition cooperative relaxation exhibits compensation behaviour. On the other hand, lowerT g and upperT g discharges were observed and their molecular nature is discussed.

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Abstract  

We investigated the features of the glass transition relaxation of two room temperature ionic liquids using DSC. An important observation was that the heat capacity jump, that is the signature of the glass transition relaxation, shows a particularly strong value in this type of new and promising materials, candidates for a range of applications. This suggests a high degree of molecular mobility in the supercooled liquid state. The study of the influence of the heating rate on the temperature location of the glass transition signal, allowed the determination of the activation energy at the glass transition temperature, and the calculation of the fragility index of these two ionic glass-formers. It was concluded that this kind of materials belong to the class of relatively strong glass-forming systems.

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Abstract  

The thermal behaviour of 2- and 4-biphenylmethanol were studied by differential scanning calorimetry (DSC). It was found that the 2-isomer shows a relatively strong resistance to crystallisation, and that it easily vitrifies on cooling. Oppositely, 4-biphenylmethanol readily crystallizes on cooling. The slow molecular mobility of 2-biphenylmethanol in the amorphous solid state was studied by DSC and by thermally stimulated depolarisation currents (TSDC). Both techniques indicate that 2-biphenylmethanol is a relatively strong glass-former, with a fragility index of ~50 in the Angell's scale.

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