Comparative Consideration on Glass Transition Characteristics of Organic and Inorganic Glasses

Abstract

Glass transition is observed on almost all materials in glassy state. Some properties change abruptly at glass transition temperature, Tg, which itself changes with experimental conditions, and in glass transition region properties or structure of glasses change with time to approach to their own equilibrium states respectively. It has been an unsolved problem whether glass transition is a thermodynamical one such as second order transition or is originated from relaxation phenomenon in freezing-in of glass structure.Results of many investigators on glass transition characteristics of various kinds of glasses (organic high polymer, chalcogenide or inorganic oxide glasses) are examined and compared. Similarities are found in the following situations, namely; 1. Glass transition is related to several mechanisms with different relaxation times and activation energies, 2. Tg changes with experimental condition in a similar fashion, 3. Many thermodynamical functions show similar behaviors in transition region and 4. “Cooperativeness” is recognized in a resembled form. On the other hand, there are some differences, namely; 1. Change of Tg with experimental condition is far more distinct in inorganic glasses, 2. Change of viscosity or relaxation time with temperature is more striking in organic glasses, 3. Cooperativeness is better distinguished in organic glasses and 4. Linear relations between temperature and log viscosity or equilibrium specific volume are realized in larger temperature range by inorganic glasses.As a result, glass transition characteristics of organic glasses are resembled to those of thermodynamical transition, and in inorganic oxide glasses transition seems to be a mere consequence of relaxation phenomenon.Following the author's opinion, these differences are originated from 1. Difference of flow-units which take part in transition, 2, Distinction in bonding forces and interference between flow-units and 3. Different degree in tendency of glass structure to freeze-in at relatively low temperatures.