Glass viscosity and structural relaxation by parallel plate rheometry using a thermo-mechanical analyser

Glass viscosity from 10(5) poises and up to an extended 10(11) poises has been successfully measured by parallel plate rheometry using a commercial thermo-mechanical analyser (TMA), Perkin-Elmer TMA-7. The viscosity data measured on a standard reference soda-lime silicate glass, NIST 710a, are in excellent agreement with the standard viscosity data of the glass supplied by the National Institute of Standards and Technology (NIST). The technique is also found very effective in monitoring the structural relaxation process in glasses. Subsequently, the relationship between glass structure and its relaxation mechanism is studied. It is found that the relaxation mechanism in the glass can be adequately represented by a double exponential function with a rapid and a slow component. The rapid and slow relaxation components are attributed to the relaxations originating from the modifier-rich and glass-former-rich regions in the glass respectively, following the modified-random-network (MRN) model of glass structure.