Scattering lights and inclination of filamentary particle in electrostatic sorting system

Abstract

We have investigated an electrostatic sorting system based on the mechanism of a cell sorter system. Particles dispersed in liquid are carried by the flow and ejected from a nozzle one by one, being kept inside the liquid column. A laser beam illuminates the liquid column just below the nozzle. When a particle is passing by there, the scattering light is produced and detected by two photomultipliers (PMTs). A computer analyzes the scattered light intensities and classifies the particle by size or its shape. The particle is flowing down to the breaking point of the liquid column, where an electrode is put close to the liquid column end. When the particle reaches this point, a pulsed voltage is applied to the electrode to make a charged droplet with the particle. This charged droplet with the particle is deflected in the uniform electric field and collected separately. As for the spherical particles it has been confirmed the particles of 5-33 /spl mu/m diameter can be sorted by size with up to 90% efficiency. For filamentary particles, it has been revealed experimentally that the scattered lights detected by two PMTs are not generated at the same time. It suggests that the time difference between two scattered light pulses is related to the particle length. In this report the particles inside the liquid column are observed by means of a video microscopic system and a single flash light, those results are combined with the scattered light patterns. The relation between the particle length and the the time difference of two scattered lights has been confirmed. The change of the inclination of a filamentary particle during flowing down the liquid column is also observed. The deformation of the liquid column due to the particle has been examined to improve the sorting efficiency.