Anomalous electrical conductivity behavior at elevated pressure in the protic ionic liquid procainamide hydrochloride.

Using broadband dielectric spectroscopy, we investigated the effect of hydrostatic pressure on the conductivity relaxation time of the supercooled protic ionic liquid, procainamide hydrochloride, a common pharmaceutical. The pressure dependence of exhibited anomalous behavior in the vicinity of the glass transition Tg, manifested by abrupt changes in activation volume. This peculiar behavior, paralleling the change in temperature dependence of near Tg, is a manifestation of the decoupling between electrical conductivity and structural relaxation. Although the latter effectively ceases in the glassy state, free ions retain their mobility but with a reduced sensitivity to thermodynamic changes. This is the first observation of decoupling of ion migration from structural relaxation in a glassy conductor by isothermal densification.