Measurement of the Translational Diffusion Constant of Nano-sized Polystyrene Spheres with Dynamic Light Scattering Techniques

Josh Hansen and Ann Jennings

University of Minnesota

Methods of Experimental Physics Spring 2012

Abstract

This experiment examined the use of dynamic light scattering using nano-sized polystyrene spheres undergoing Brownian motion. The goal was to determine the translation diffusion constant and compare it to the theoretical Stokes-Einstein relationship. By analyzing the power spectrum, the half width half max was given as G, which is proportional to the diffusion constant, D. When the data was plotted as G versus diameter, the experimental results showed a -1.61s difference from theory. G is proportional to the inverse of the diameter of the spheres. The theoretical Gd=(2.77±0.063)x105nm/s. The experimental Gd=(2.63±0.059)x105nm/s.