Sub-Tg relaxations of dipolar solutes in glass forming solvents

Johari-Goldstein(or JG) relaxation of rigid molecular solute acetone in various glass forming solvents was studied, and compared with the relaxation of acetone molecules occurring in the cages of acetone clathrate hydrate. The activation energy (ΔEβ) of the JG-process for the solute increases with a decrease in the size of the cage of the host (solvent) matrix, and increase in interaction of the solute molecules with the solvent. We have also studied the sub-Tg relaxation(s) due to some flexible molecular solutes, viz. some esters of phthalic acid. These solutes in isopropylbenzene matrix exhibit only one sub-Tg relaxation, whereas in o-terphenyl matrix exhibit an additional sub-Tg process which may be identified with JG type of relaxation. This observation lead us to the conclusion that the β-process observed in the glassy states of these pure solutes is predominantly intramolecular in nature.