Critical temperature shift in pure fluid SF6 caused by an electric field

A systematic study of the effect of an electric field on the critical temperature of a pure fluid is made for the first time to our knowledge. An ac electric field is applied to a spherical capacitor filled with SF6 at its critical density, while the temperature is slowly ramped down through its critical temperature T(c). By continuously observing the light transmission through the fluid during the temperature ramp, a shift in T(c), DeltaT(c), is found at various electric fields. By shining the light vertically through the fluid, we utilize the density gradient induced by the fluid's weight to compensate for the effects of density changes from electrostriction. This technique effectively keeps the system at constant critical density with respect to the observation of T(c). We observe an increase in T(c) as expected from thermodynamic stability and renormalization group theory, but quantitatively larger by an order of magnitude.