Electrical Field Effect on the Critical Opalescence

The free energy involved in the concentration fluctuations of a liquid mixture is changed by an electric field. The effect becomes observable near the critical point. It increases with decreasing distance from the critical temperature and it is proportional to the square of the field intensity and to the second derivative of the dielectric constant with respect to the concentration. Temperature as well as field strength dependence are in agreement with a theory built along classical lines. The effect can be interpreted as a shift of the critical temperature and the sign of this shift is also predicted correctly. Experiments performed with a field intensity of 45 000 V/cm on the system nitrobenzene-2,2,4-trimethylpentane give a value of 0.015° for this shift (which is a depression), while the theory predicts the same.