Radial migration (particle motion transverse to streamlines) in a system which combines frequent entry, straight pore, and exit regions were investigated experimentally for small particle and pore sizes. Pore diameters were less than 30 μm and typical particle to pore diameter ratios were about 0.25. Our new modification of the resistive pulse technique based on pressure reversal, extends this experimental technique to also include single-particle flow dynamics. By pressure drive, a particle in an electrolyte enters a current-carrying pore and an increase in resistance proportional to the particle volume is detected. When the particle exits the pore, the pressure can be reversed such that the particle re-enters the pore. Detailed studies of particle flow properties in a size range relevant to flow in porous media is now possible. The emphasis in this investigation is on radial migration. The effect of particle sedimentation has been negligible, while particle diffusion becomes significant for submicron particles. The measured evolution of the transit time as the particle migrates compares well with an empirical relationship for the migration velocity first proposed by Segré & Silberberg (1962 a, b) and later verified by Ishii & Hasimoto (1980). Entrance and exit effects do not seem to be important for long pores, the results scale very nicely when the pore length is changed.
Pores with Undulating Diameter for Multipronged Characterization of Single Particles and Cells in Resistive-Pulse Technique
