Dielectric loss spectra are reported for $\alpha$-tocopherol acetate (an isomer of vitamin E) in the supercooled and glassy states. The $\alpha$-relaxation times, ${\tau }_{\alpha }$, measured over a 190° range of temperatures, $T$, at pressures, $P$, up to $400\mathrm{MPa}$ can be expressed as a single function of $T{V}^{3.9}$ ($V$ is specific volume, measured herein as a function of $T$ and $P$). At ambient pressure, there is no dynamic crossover over eight decades of measured ${\tau }_{\alpha }$. The relaxation spectra above the glass transition temperature $T_g$ show ionic conductivity and an excess wing on the high-frequency flank of the $\alpha$-relaxation loss peak. Temperature-pressure superpositioning is valid for the $\alpha$ process; moreover, the peak shape is constant (stretch exponent equal to 0.65). However, application of pressure changes the shape of the dielectric spectrum at higher frequencies due to the shift of the excess wing to form a resolved peak. Additionally, another relaxation process, absent at atmospheric pressure, emerges on the high-frequency side of the $\alpha$-process. We propose that this new peak reflects a more compact conformation of the $\alpha$-tocopherol acetate molecule. Drawing on the coupling model, the experimentally determined relaxation times, activation energy, and activation volume for the Johari-Goldstein process are compared to values calculated from the properties of the $\alpha$ relaxation. The agreement is generally satisfactory, at least for $T<T_g$.

• Received 26 July 2006

DOI:https://doi.org/10.1103/PhysRevE.75.011903