Dynamic light scattering studies of concentration fluctuations in aqueous t-butyl alcohol solutions

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Abstract
Dynamic light-scattering measurements using photon correlation spectroscopy have been performed on four different concentrations of t-butyl alcohol in water; 7.25, 13.2, 20.1, and 26.0 mol %. Temperatures ranged from as low as −16 °C in the supercooled regime to as high as 72 °C. Mutual diffusion constants of the concentration fluctuations were extracted from the light-scattering data. Viscosity measurements were also performed on these solutions over these temperature ranges. The correlation length of the concentration fluctuations determined from these measurements increased with increasing temperature, leveled off near room temperature and then showed another increase at lower, especially supercooled temperatures. These behaviors suggested critical demixing or consolute points should exist at both temperatures above the equilibrium boiling and below the freezing points of the mixture. The high temperature critical point is probably due to t-butyl alcohol and water association, whereas the low temperature critical point is most likely due to water–water self-associating. The results are discussed in terms of the unusual critical-phenomena-like properties of supercooled pure water and the possibility that these unusual properties are due to water–water association in the form of clathrate-type structure.