EXPERIMENTAL-STUDY OF THE NATURE OF THE GLASS-TRANSITION PROCESS IN MONOHYDROXY ALCOHOLS

The nature of the glass transition process in six monohydroxy alcohols, viz., the isomers of butanol, 2-propanol, and 3-methyl-1-butanol had been studied in detail using dielectric spectroscopy (frequency range 10(+6)-10(-3) Hz) and differential scanning calorimetry (DSC). Measurements were made down to a temperature of 77 K in dielectric experiments and a temperature of 95 K in DSC. These results together with the published microwave data on these liquids reveal the existence of two glass transition processes-one due to the hydrogen bonded network which is very dominant and the other one due to the nonhydrogen bonded molecules, which is much weaker. Associated with the latter process, there is a secondary (or beta-) relaxation process whose activation energy varies from 4.8 to 6.7 kcal/mol which is dependent on the shape and size of the liquid molecules. In addition to the beta process, all the alcohols revealed yet another sub-T(g) (gamma) process whose activation energy varies from 2.1 to 2.6 kcal/mol and is found to be little dependent on the molecular shape. These results perhaps indicate that the beta process is somehow connected to the relaxation of the free monomeric molecule and the gamma process to that of hydroxyl group rotation, respectively.