Change in molecular dynamics with structures of the trialkyl phosphates and in mixtures with ortho-terphenyl

Abstract The dielectric study of tri-alkyl phosphates had elucidated that the dynamics of relaxations depends on the strength of intermolecular interaction/coupling, which in turn depends on the chemical structure of phosphates. In the same spirit, we examine these phosphates of about 10 mol% in mixtures with the o-terphenyl host. The spectra coming exclusively from the rotational dynamics of phosphates revealed two secondary processes in addition to the primary relaxation. The slower β-relaxation is new in the mixtures, and is identified as the intermolecular Johari-Goldstein-Extended (JGX) β-relaxation with relaxation time τβ(Tg) having strong connection to τα(T) of the α-relaxation. The ratio τα(Tg)/τβ(Tg) decreases monotonically with increasing length of the alkyl chains in higher members. The results of the mixtures reaffirm the small intermolecular coupling in the pure phosphates. The deduction is attempted to explain the success of ultrastable glass formation in TMP and failure in TEP and TBP.