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Broadband boundary effects on Brownian motion
Jianyong Mo1, Akarsh Simha1, Mark G Raizen1
1Center for Nonlinear Dynamics and Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA.
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|January 15, 2016
Summary
Boundary effects on Brownian motion were measured for silica spheres in water. Confinement impacts both short and long timescales, altering particle dynamics and thermal forces, enabling new microscopy techniques.
Area of Science:
- Physics
- Physical Chemistry
- Soft Matter Physics
Background:
- Brownian motion is crucial for fluid dynamics and applications.
- Boundary effects on particle motion in confined fluids are not fully understood across all timescales.
Purpose of the Study:
- To comprehensively measure and understand the effects of a nearby wall on Brownian motion.
- To investigate how surface confinement influences particle dynamics at both short and long timescales.
Main Methods:
- Utilizing high-bandwidth measurements of an optically trapped micrometer-sized silica sphere.
- Analyzing Brownian motion in water near an approximately flat wall.
Main Results:
- Observed anisotropic Brownian motion at short distances from the wall.
- Found surface confinement affects both diffusive and ballistic regimes.
- Demonstrated faster decay of the velocity autocorrelation function compared to bulk fluid.
- Identified that thermal force loses its 'color' at low frequencies due to no-slip boundary conditions.
Conclusions:
- Surface confinement significantly alters Brownian motion dynamics across various timescales.
- The observed phenomena provide insights into particle-fluid interactions near boundaries.
- This understanding can facilitate the development of novel 3D microscopy techniques using particles as sensors.
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