Brownian Dynamics of a Sphere Between Parallel Walls

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Original Entry by Tom Dimiduk, AP225 Fall 2010

Brownian Dynamics of a Sphere Between Parallel Walls E. R. Dufresne, D. Altman and D. G. Grier

Soft matter Keywords

Brownian Motion, Surface


Video microscope setup used to make these measurements. B) shows that their sample was a 2cm x 1 cm cover slip on a glass slide. It was anchored with an 8 micron gap above the slide using norland optical adhesive. Glass capillaries at either end allow flow through the cell. A) Shows the slide as imaged in an inverted microscope.

To the right is a diagram showing my best interpretation of the apparatus the authors used to make high resolution measurements of the brownian motion of a sphere confined along one dimension by two glass planes 8 microns apart. They positioned a 1 micron sphere in a precise position using an optical trap, then released it to study motion. They imaged with a video microscope at 60 Hz and used particle centroiding to obtain a resolution of 20 nm in x and y. They obtained z information by repeating the experiment releasing the particle from the same location with the microscope focused at differing heights. They measure distance from the wall by running a steady poiseuille flow and observing its effect on the particle velocity.

z), fit to eq. (1) for D_i(h)."