Static and dynamic light scattering experiments with an iso-butoxyethanol/water mixture of critical composition

✍ Scribed by S. Limberg; L. Belkoura; D. Woermann

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 928 KB
• Volume: 73-74
• Category: Article
• ISSN: 0167-7322
• DOI: 10.1016/s0167-7322(97)00069-x

✦ Synopsis

Results of static and dynamic light scattering as well as of viscosity measurements are reported. They are carried out with an i-C,E,/water mixture of critical composition in the vicinity of its lower critical point (y, = 0.3 180, mass fraction of i-C,E,; T, = 26.450 "C). This point is approached from temperatures T < T,. The value of the critical amplitude 5, of the correlation length of local concentration fluctuations obtained from static light scattering experiments is combined with the known values of the critical amplitude ou of the liquid/liquid interfacial tension and the critical amplitude A,,, the heat capacity at constant pressure per unit volume cp to calculate the values of the universal amplitude ratios R(o,<) and R(c,,,<). The critical amplitudes are material-dependent quantities. The calculated values of R(o,<) and R(c&) are consistent with their theoretical predictions. The "hydrodynamic" correlation length <,,,, of concentration fluctuations is obtained by combining experimental viscosity and mutual diffusion coefficient data. The tLd values are in agreement with the corresponding values of E, obtained from static light scattering experiments. The calculation of <,,d is based on an equation analogous to the Stokes-Einstein relation. The data of the diffusion coefficient are obtained from dynamic light scattering experiments. The material dependent critical amplitude Q, of the viscosity is found to have a value typical of simple binary mixtures of low molar mass components. It is concluded that formation of aggregates of i-C,E,molecules

and/or i-C,E, and water molecules in an i-C,E,/water mixture of critical composition does not influence the critical properties of this system. The properties are in agreement with that predicted by the universality concept of critical phenomena.