Critical opalescence of liquid mixtures

Abstract

A critical review of the theory of secondary scattering proposed by Rousset in order to explain the finite value of the depolarisation of the opalescence of liquid mixtures is given. Further consequences of the theory of secondary scattering have been worked out and it is found that the experimental results obtained are not in accordance with the conclusions of the theory. From the results obtained it has been concluded that in the neighbourhood of the critical solution temperature of liquid mixtures the molecules have got a tendency to group themselves together in the form of clusters and that the finite value of the depolarisation of the opalescent light arises due to this fact. In the neighbourhood of Tc the secondary scattering has little or no effect on the depolarisation factor, although it may have an appreciable effect for ΔT<0.1° C. where ΔT=T-T_c. The measurements of the depolarisation factors ρ _u ,ρ _v and ρ _h for three binary mixtures and one ternary mixture have been made over a range of temperature of 30° above T_c. The results obtained fully confirm the author's earlier report regarding the existence of clusters in liquid mixtures not only at the critical solution temperature but also at temperatures considerably removed from it. The theory proposed by Gans has been discussed in relation to the experimental results obtained by the author and the limitations of the theory have also been pointed out. The bearing of the results on the anomalies of viscosity, electric birefringence, etc., noticed by the earlier investigators in the vicinity of the critical solution temperature has been discussed in detail.