A new dielectric measurement approach utilizing a differential interdigitated electrode (IDE) cell and dual-channel impedance scheme has been implemented. To show the practicability of this new approach, we performed measurements on a 600 nm film of a supercooled indomethacin (IMC). In dielectric relaxation, an oscillating electric field is applied across a sample. The current required to maintain the field at different frequencies is measured and allows the calculation of the in-phase and out-of-phase dielectric response. The latter shows a peak at the frequency where molecular reorientation occurs.
Dielectric measurements were carried out to during the isothermal annealing of vapor-deposited stable glasses of IMC. The annealing temperature was slightly above the glass transition temperature Tg = 315 K.
During isothermal annealing, the liquid volume fraction derived from the relaxation amplitude, Δε, increases linearly with time, consistent with previous measurements based on other experimental techniques. This happens because the stable glass transforms into the supercooled liquid via a propagating front that moves at a constant velocity from the free surface towards the substrate.
These new capabilities will also allow the investigation of secondary relaxation processes in stable glasses.