Brownian motion overview

Total internal reflection microscopy (TIRM) was introduced in 1987 by Prieve et al. [343]. TIRM allows to probe the interaction of a single microsphere with a transparent flat plate. In a TIRM experiment, a microsphere is allowed to sediment toward the plate. The technique relies on repulsive forces between sphere and plate. This repulsion will typically result from electric double layer or steric forces. They keep the sphere from getting into contact with the plate. Thermal fluctuations will constantly change the precise distance. The distance between sphere and plate is monitored by the light intensity scattered from the particle when illuminated by an evanescent wave and can be determined with a resolution of w 1 nm. By recording the fluctuations in vertical position of the sphere due to Brownian motion, the potential energy of interaction and the diffusion coefficient of the sphere can be deduced. For overviews of the technique, see Refs [344, 345]. 

The purpose of this paper Is to present a brief overview and description of a modelling approach we are taking which Is aimed at developing a quantitative understanding of the mechanisms and separation capabilities of particle column chromatography. The main emphasis has been on the application of fundamental treatments of the convected motion and porous phase partitioning behavior of charged Brownian particles to the development of a mechanistic rate theory which can account for the unique size and electrochemical dependent separation behavior exhibited by such systems. 

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