Static Light Scattering Experiments with a Critical Isobutyric Acid (COOD)/Deuterium Oxide Mixture Above its Critical Solution Temperature

Static light scattering experiments are carried out with an almost critical mixture of isobutyric acid (COOD) and D 2 O (mole fraction of isobutyric acid (COOD) x DA = 0.11; temperature of phase separation T P = 45.9°C) to determine the critical amplitude of local concentration fluctuation. The following results are obtained: critical amplitude of local concentration fluctuations ξ 0 = (3.1 ± 0.2) · 10 −8 cm; critical exponent of correlation length of local concentration fluctuations: ν = 0.63 ± 0.01; critical exponent of susceptibility: γ = 1.26 ± 0.01. The values of the critical exponents v and γ are in good agreement with theoretical values predicted for binary liquid mixtures. The system‐specific parameter (0 of the system isobutyric acid (COOD)/D 2 O is slightly smaller (about 10%) than the corresponding value of the system isobutyric acid (COOH)/H 2 O ( x cHA = 0.11; T c = 26.1°C) reflecting differences between the intermolecular forces in the two systems.