Glass formation in organic binary liquids studied using differential scanning calorimetry

Abstract

Differential scanning calorimetric (DSC) studies have been performed on binary mixtures of organic liquids at temperatures down to 100 K over the entire concentration range. The liquids investigated are simple liquids such as chlorobenzene and bromobenzene in cis-decalin and o-terphenyl. All the binary liquids exhibited a simple eutectic phase diagram. Glass formation was studied in detail by varying the cooling rate, degree of crystallinity and concentration. In liquids where the components are bad glass-formers on their own, the glasses formed are mixed glasses and the probability of glass formation is maximum for intermediate concentrations.Over a wide range of concentration, the liquid mixtures freeze into a glassy state around the same temperature. The dominant freezing in the liquid mixtures occurs at the eutectic concentration. This is supported by studying the freezing and associated enthalpy for the eutectic mixture. For faster cooling rates almost all the binary liquids exhibit two or more glass-transition processes, and these are discussed on the basis of the phase diagram. The nature of glass formation in binary liquids whose components are good glass formers is also discussed.