College of Liberal Arts & Social Sciences Theses and Dissertations

Graduation Date

8-2010

Document Type

Thesis

College/Department Conferring Degree

Physics

Keywords

diffusion, brownian motion, colloidal suspensions, viscous drag, stokes law

Abstract

The theories of Brownian motion and diffusion are often treated as separate idea, though Brownian motion is believed to cause diffusion. Both theories were initially studied separately in this project via two experiments; the theories were then studied in conjunction. The Brownian motion experiment examined milk fat globules and Cabosil particles in colloidal suspensions under a microscope, following their trajectory for 10 seconds. A flow model was developed to determine the diffusion coefficients. Drag coefficients revealed the geometry is correlated with the diffusion coefficients. The Diffusion experiment used a custom-made, thermally isolated chamber to study diffusion in the horizontal and vertical planes. Diffusion in the vertical direction took approximately 100 times longer than the horizontal. the two theories were then linked by using the diffusion data to determine the microscopic water molecule radius. The horizontal data agreed within uncertainty of the accepted value for the water molecule radius, while the vertical direction data did not. Gravity, particle geometry, and edge effects are suspected of affecting the rate of diffusion as suggested by its demonstrated influence on the Brownian motion of colloidal particles.

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