The Correlation between Reduced Glass Transition Temperature and Glass Forming Ability of Undercooled Polymeric Glasses

Abstract

The thermodynamic behaviour of glass forming undercooled melt have been studied by analysing the temperature dependence of the Gibbs free energy difference (G) for six poly meric glass forming materials (O-terphenyl, Tri-α-naphthyl benzene, Glycerol, Ethanol, 2-methylpentane and Phenyl salicylate (salol)) between the undercooled melt and the corresponding equilibriu m solid phases. The expression obtained by expanding free energies of the undercooled liquid and solid phases of the materials in the form of Taylor's series expansion. The procedure for the estimat ion of the ideal glass transition temperature has been reviewed together its importance in the glass forming ability of materials. The glass forming ability of undercooled materials is also explained in terms of ratio o f reduced glass transition temperature and ideal glass transition temperature. It has also reported that Glycerol has the largest melt ing interval with the poorest glass forming ab ility among these six poly mers. It has also been found that the best polymeric glass forming materials are at near eutectic composition. There is a strong correlation between glass forming ability of these polymeric materials. The thermodynamic behaviour of glass forming poly meric melts has been studied employ ing the expressions based on Taylor's series expansion and it is found that the expression for G, obtained are capable to explain temperature dependence of the thermodynamic quantities (G, H and S ) o f g lass forming poly meric melts quite satisfactorily. It is quite interesting to see the response of expression obtained on the basis of Taylor's series expansion in exp laining the temperature dependence of the thermodynamic quantity G for glass forming organic liquids. The present study is for the Gibbs free energy difference (G) between liquid and solid phases for glass forming organic melts by calculating G for six d ifferent samp les of organic glasses; o-terphenyl (o-ter), tri--napthyle benzene (tri--NB), phenyl salicylate (salo l), glycero l, ethanol and 2-methylpentane (2-mp) in the temperature range Tm to Tg in the frame of expression based on Taylor's series expansion. The expression for the entropy difference  S based on Taylor's series expansion has been further emp loyed to find