Phoretic and Radiometric Phenomena

摘要: There are a number of forces associated with microparticles that either not encountered or negligible in macroscopic systems, and some these can be much larger than the gravitational force. For example, if you sit darkened room beam light slanting down through an opening curtain window shade, might notice one interesting forces. Small dust particles often seen to move up toward source. Although convection air well cause such motion, phenomenon observed still air. Ehrenhaft (1909, 1910, 1917, 1918) recognized small particle suspended gas source direction propagation beam. He attributed firstorder electromagnetic effect, but this photophoretic force, as called it, is now understood caused by radiometric Absorption energy produce anisotropic internal heating, molecular collisions surface result net momentum transfer causes force on particle. If illuminated from back heated, thereby producing towards source, process negative photophoresis. When away it positive