Molecular dynamics of poly(propylene) glycol in nanometer confinements

Dielectric spectroscopy and temperature modulated DSC are employed to study the molecular dynamics (dynamic glass transition) of oligomeric poly(propy lene) glycol (PPG) melts (M-W = 1000, 2000, 3000 and 5000) confined to nano porous glasses (pore sizes 2.5, 5.0, 7.5 and 20 nm). For large pore sizes a speeding up of the molecular dynamic compared to the bulk state is observe d which is already known for low molecular glass forming liquids. For small er pore sizes the molecular dynamics is slower than in the bulk. The observ ed behavior is nearly independent of the molar mass and of the treatment of internal glass surfaces. The experimental results are discussed in the fra me of an interplay of confinement and packing effects. Moreover a length sc ale of 1.5 nm is estimated as lower bound for the glass transition.