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Velocity Fluctuations in Sedimenting Brownian Particles
Johannes Möller1, Theyencheri Narayanan1
1ESRF-The European Synchrotron, 38043 Grenoble, France.
Physical Review Letters
|May 27, 2017
Summary
Dynamics in sedimenting colloidal suspensions transition from advective to diffusive motion before a macroscopic front emerges. This study reveals insights into transient velocity fluctuations using multispeckle ultrasmall-angle x-ray photon correlation spectroscopy (USA-XPCS).
Area of Science:
- Soft Matter Physics
- Colloid Science
- Fluid Dynamics
Background:
- Sedimentation of colloidal particles is a fundamental process in fluid dynamics.
- Understanding the transition dynamics before macroscopic front formation is crucial.
- Charge-stabilized Brownian particles exhibit complex behaviors during sedimentation.
Purpose of the Study:
- To investigate the gradual transition of dynamics in sedimenting colloidal suspensions.
- To elucidate the mechanisms behind transient velocity fluctuations.
- To demonstrate the capabilities of multispeckle ultrasmall-angle x-ray photon correlation spectroscopy (USA-XPCS) in probing these dynamics.
Main Methods:
- Utilizing multispeckle ultrasmall-angle x-ray photon correlation spectroscopy (USA-XPCS).
- Analyzing the dynamics of charge-stabilized Brownian particles in sedimenting suspensions.
- Probing temporal development of fluctuations at low Peclet numbers (<1).
Main Results:
- Advective motions were observed to dominate early-stage colloid dynamics.
- A gradual decay of advective currents and a rise in diffusive motions were detected over time.
- The study captured the transition from advective to diffusive dynamics before macroscopic sedimentation front formation.
Conclusions:
- The dynamics in sedimenting suspensions undergo a gradual transition from advective to diffusive regimes.
- Multispeckle USA-XPCS provides novel insights into the transient nature of velocity fluctuations in sedimentation.
- This technique enhances experimental capabilities for studying complex fluid dynamics at the colloidal scale.
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