Observation of the relaxation of composition fluctuations in a binary liquid mixture

• Published in: Physica A 1983-01, Vol.118 (1), p.268-281
• Main Authors: Easwar, N., Joshua, M., Maher, J.V., Goldburg, W.I.
• Format: Article
• Language: English
• ISSN: 0378-4371; 1873-2119
• DOI: 10.1016/0378-4371(83)90192-9

Light scattering was used to study the decay of concentration fluctuations in a critical mixture of isobutyric acid and water. The aim of the experiment was to study the dynamic interaction between composition and velocity in the mixture. At large wavenumber, the structure factor S( k, t) is observed to decay exponentially, with a relaxation rate somewhat smaller than the equilibrium value. At small k, however, there is a marked departure from the exponential relaxation one expects in the absence of coupling between composition and velocity. Also measured was the spinodal ring diameter, k m, as a function of the total scattered intensity, C tot ( t) = (2 π) −2 ∫ S( k, t) k 2 dk. A calculation of Ruiz, based on the above coupling effect, predicts a linear variation of In k m( t) with C tot( t) and such a linear variation is observed.