Measuring Absolute Velocities from Nonequilibrium Oscillations via Single-Detector 3D Dynamic Light Scattering

Area of Science:

• Soft Matter Physics
• Colloidal Science
• Fluid Dynamics

Background:

• Out-of-equilibrium colloidal systems exhibit complex dynamics.
• Understanding particle drift velocity is crucial for various applications.
• Thermally induced convection significantly impacts particle motion.

Purpose of the Study:

• To investigate particle dynamics in colloidal suspensions under thermal convection.
• To establish single-detector 3D dynamic light scattering (3D DLS) as a reliable technique for measuring drift velocity.
• To provide a comprehensive explanation for observed oscillations in light scattering data.

Main Methods:

• Utilized single-detector 3D dynamic light scattering (3D DLS).
• Experimental investigation of colloidal particles in a convecting fluid.
• Corroboration with theoretical modeling.
• Validation through fluid dynamics and Brownian dynamics simulations.

Main Results:

• Observed well-defined frequency oscillations in the autocorrelation function of scattered intensity.
• Attributed oscillations to directed particle motion caused by fluid convection.
• Experimental results showed excellent agreement with theoretical and simulation data.

Conclusions:

• Single-detector 3D DLS is a robust method for determining drift velocity in nonequilibrium systems.
• The study provides a solid explanation for convection-induced particle dynamics.
• Findings are applicable to various nonequilibrium scenarios beyond diffusion-convection, including external fields.