Dielectric properties of vapor-deposited propylbenzenes

Abstract

Dielectric susceptibility data of vapor-deposited films of iso-propylbenzene (IPB) and npropylbenzene (NPB) have been recorded across a wide range of deposition temperatures, Tdep, mostly below the glass transition temperature, Tg. The results for the real and imaginary components of dielectric susceptibility are compared with recently published results for 2-methyltetrahydrofuran (MTHF). Common to all three systems are: (i) increased kinetic stability seen as higher onset temperature for the transformation to the liquid state for Tdep  0.85Tg, (ii) the reduction of the dielectric loss ('') for as-deposited glasses, a signature of increased packing density that is maximal for Tdep  0.85Tg, and (iii) a reduced level of the storage component (') for as-deposited glasses, an effect that is almost deposition temperature invariant for Tdep < Tg. Material specific behavior is observed when heating the as-deposited films to 1.2Tg: IPB and NPB transform directly into the ordinary liquid state if judged on the basis of dielectric susceptibility, whereas MTHF has been reported to enter an unusual liquid state prior to a liquid-liquid transition at higher temperatures. These results are discussed in the context of the curious scattering results reported by Ishii et al. for some benzene derivatives, which hint at a liquid-liquid transformation.

Vapor-Deposited Thin Films: Studying Crystallization and α-relaxation Dynamics of the Molecular Drug Celecoxib

“…As concluded from that study, when heated above T g , vapor-deposited MTHF does not transform into the same supercooled liquid state as that reached by cooling the ordinary melt. Therefore, it has been speculated that vapor deposition might promote polyamorphism and result in seeing distinct long-lived metastable states with different dynamics. , CXB also possesses hydrogen bonding possibilities (two oxygen atoms of the sulfonamide group, fluorine atoms of the CF3 group, and two nitrogen atoms in the heterocyclic ring). Variable hydrogen-bond formation leads to an intermolecular association within CXB molecules which includes five-membered structures.…”