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Diffusion

Perhaps the simplest quantity to measure with blinking optical tweezers is a Brownian sphere's self-diffusion coefficient [25]. The sphere's d-dimensional trajectories tex2html_wrap_inline732 during free intervals labeled by i can be used to estimate its self-diffusion coefficient D, for example using the Einstein-Smoluchowsky equation,

  equation34

Carefully controlled single-particle diffusion measurements serve as baselines for more complex measurements. Despite their simplicity, they also promise new insights into fundamental colloidal processes in the near future. For example, the theory of charged particles' diffusion in the presence of dissolved simple ions is well developed [28] but has been tested primarily through measurements on bulk suspensions.



David G. Grier
Mon Feb 17 21:35:47 CST 1997