Viscosity Measurement and Relaxation Mechanism of Glasses Far Below the Glass Transition Temperature.

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It is generally believed that viscous flow never occurs in a glass below glass transition temperature because of rigid state in which atomic or molecular motions are frozen. However, volume shrinkage or crystallization have been observed even below the glass transition temperature.In the present study, we proposed the new method of viscosity measurement far below the transition temperature in the range of 10^<14>-10^<18> Pa・s. The glass fiber of 0.1 mm diameter was wound and kept at temperatures far below the transition range. By measuring the remained curvature radius after the heat treatment as a function of the heat treatment time, the viscosity was determined. The viscosity thus determined is not an intrinsic value since the glass is thermodynamically non-equilibrium state and the properties depend on thermal history. In addition a glass should be treated as a viscoelastic substance.The glass fiber was heated with various temperatures and times before viscosity measurement, and the relaxtion process at low temperature was analyzed based on the non-lonear relaxation function from the viscosity change with heat-treatment. It was found that the apparent viscosity and relaxation time as well as the activation energy for relaxation increase remarkably with heat-treatment. The relaxation spectrum becomes narrow and sharp. In addition, it was tried to separate the contributions of delayd elasticity and viscous flow.