Dielectric studies of glass transition in confined oligomers of propylene glycol

We report the results of the detailed studies of confinement on the glass transition of propylene glycol (PG) and its oligomers (PPGs). The molecular weight (MW) of the oligomers was 400, 1200 and 2000. Vycor glass (VG), characterized by a narrow distribution of pore diameters around 4.0 nm, was used for confinement. Both native and chemically treated glasses to render the inner pore surfaces hydrophobic were used. The techniques employed include thermally stimulated depolarization currents (TSDC) and broadband dielectric relaxation spectroscopy (DRS). Compared to bulk liquids, confinement was found to cause a shift of the α relaxation, associated with the glass transition, to higher frequencies/lower temperatures and a broadening of the response. Cooperativity effects are thought to be responsible for these changes