field-flow fractionation techniques a colloidal material is Sedimentation field-flow fractionation (SdFFF) has proved to placed into a thin, rectangular slit. A force, which will act be a very powerful technique for the particle size analysis of submion the colloidal material, is imposed perpendicular to the crometer hydrosols. Recently reports have been published on the thin dimension of the slit, causing the colloidal material to analysis of coagulated latex samples via SdFFF. In these investigamigrate to one of the walls (henceforth called the accumulations the coagulated particles do not behave as predicted by SdFFF tion wall) of the slit. This causes a concentration gradient theory but elute from the SdFFF channel more rapidly than exacross the thin dimension of the slit resulting in back diffupected. This behavior has been ascribed to the effect of particle sion of the colloidal material. An equilibrium distribution of shape on retention. In this investigation samples of monodisperse the colloidal material is achieved when the back-diffusion polystyrene latices were coagulated under shear to yield particles which were all alike in shape (rod-like). Analyzing these samples flux is exactly equal to the flux caused by the force field. via SdFFF indicated that retention is determined by the maximum The fluid within the slit then is put into motion with a laminar dimension of the particle rather than by any average size. For flow field established parallel to the narrow dimension. Thus, highly retained particles there was an additional effect acting to particles whose equilibrium distribution from the accumulashorten the expected retention time due to the tumbling motion tion wall places them, on average, further from the wall will of the rod-like particles in the shear flow through the SdFFF tend to move through the slit at a higher average velocity channel.