Sedimentation Field-Flow Fractionation of Nonspherical Particles

Sedimentation field-flow fractionation (SdFFF) has proved to be a very powerful technique for the particle size analysis of submicrometer hydrosols. Recently reports have been published on the analysis of coagulated latex samples via SdFFF. In these investigations the coagulated particles do not behave as predicted by SdFFF theory but elute from the SdFFF channel more rapidly than expected. This behavior has been ascribed to the effect of particle shape on retention. In this investigation samples of monodisperse polystyrene latices were coagulated under shear to yield particles which were all alike in shape (rod-like). Analyzing these samples via SdFFF indicated that retention is determined by the maximum dimension of the particle rather than by any average size. For highly retained particles there was an additional effect acting to shorten the expected retention time due to the tumbling motion of the rod-like particles in the shear flow through the SdFFF channel.