Oscillatory Measurements at Temperatures Above 600°C: A Case Study on the Visco-Elasticity of Reference Glass DGG 1
Oscillatory rheometry provides a robust measure of liquid-solid transitions by the comparison of viscous and elastic moduli both with constant and changing temperatures. In addition to trace e.g. crystallization processes and crosslinking reactions, the method is particularly suited to characterize glass transitions. Here, oscillatory rheometry outperforms both differential scanning calorimetry and rotational rheometry. In the former case, measurements often need to be performed at unrealistically high cooling rates; and in the latter case, glass transition temperature (Tg) is arbitrarily defined as a viscosity value of 10¹² Pa∙s, which is intended to represent a relaxation time of ~100 s.
In contrast, high temperature oscillatory rheometry provides a strong definition of the glass transition and allows the determination of Tg with variable cooling rates (including isothermal measurements) and with applied mechanical deformation (representing processing conditions).
Oscillatory rheometry is a well-established technique used to quantify visco-elastic behavior of various materials ranging from ideally viscous liquids, like water, over viscoelastic materials like polymers, paints, coatings and food, to ideally elastic solids, like steel. In addition, the method is capable of measuring the temperature-dependent visco-elasticity, thereby revealing phase transitions like crystallization, melting or glass transition. In contrast to rotational viscometry which provides one value (viscosity), oscillatory rheometry provides additional insight into the character of the phase transition by two values (viscous modulus G″ and elastic modulus G′) to describe the materials’ response to oscillating shear deformation.
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