Multiexponential decay autocorrelation function in dynamic light scattering in near-critical ternary liquid mixture

Area of Science:

• Thermodynamics
• Fluid Dynamics
• Materials Science

Background:

• Ternary liquid mixtures exhibit complex transport properties, especially near critical solution points.
• Understanding these properties is crucial for various chemical and physical processes.

Purpose of the Study:

• To develop a theoretical model for calculating the dynamic structure factor of ternary liquid mixtures.
• To evaluate and classify transport properties near a critical solution point.
• To associate experimentally observed hydrodynamic relaxation modes with specific diffusion processes.

Main Methods:

• Utilized the theory of thermodynamic fluctuations and linearized hydrodynamic equations.
• Employed dynamic light scattering experiments to measure autocorrelation functions.
• Determined two effective diffusivities, D(1) and D(2), from experimental data.

Main Results:

• The theoretical model successfully predicts two hydrodynamic relaxation modes near the critical solution point.
• Experimentally, two effective diffusivities, D(1) and D(2), were identified.
• One mode corresponds to thermal diffusion and the other to mass diffusion.

Conclusions:

• The developed model provides a framework for understanding diffusion in ternary mixtures.
• The study distinguishes between thermal and mass diffusion contributions to transport properties.
• In the incompressible limit, these diffusivities decouple into the thermodiffusion coefficient D(T) and mutual mass diffusion coefficient D(ij).