Bhajendra N. Barman

CONTINUOUS FRACTIONATION OF GLASS MICROSPHERES BY GRAVITATIONAL SEDIMENTATION IN SPLIT-FLOW THIN (SPLITT) CELLS

ABSTRACT Split-flow thin (SPLITT) separation cells, consisting of submillimeter thick rectangular channels having now splitters at both inlet and outlet ends, were operated continuously using the earths gravitational field as a driving force to prepare narrow fractions from polydisperse micron-size glass bead populations. Equations arc shown that make it possible to achieve a binary fractionation around a specified cutoff particle diameter by the control of inlet and outlet flowrates. Using a single separation cell, each narrow fraction was obtained by a two step fractionation. one dividing the panicle population around the upper desired limit and the other around the lower desired limit of particle diameters. The clean fractionation by SPLITT cell operation was verified by scanning electron microscopy, which also provided the mean particle diameter and the coefficient of variation for each fraction. The consistency of size distribution results was also examined by steric field-flow fractionation.

Resolution of colloidal latex aggregates by sedimentation field-flow fractionation

Abstract The observation of a repetitive series of peaks while analyzing two different samples of poly(methyl methacrylate) colloidal latex spheres by sedimentation field-flow fractionation strongly suggests that part of the latex population has aggregated into doublets, triplets, and higher-order particle clusters. The aggregation hypothesis is confirmed for the two samples both by retention calculations and by electron microscopy. It is shown that the resolution of the latex clusters is influenced by flow velocity in a manner predicted by theory but that such resolution is limited by the polydispersities of the two latex samples. Polydispersity values are obtained using plate height versus flow velocity measurements and are shown to be consistent with the different resolution levels observed for the two colloids. A detailed analysis of the results shown that steric effects play an increasing role as cluster size increases. The steric role in this study is examined at some length.

Colloid characterization by sedimentation field-flow fractionation: VII. Colloidal aggregates

Abstract This study addresses the scope and limitations of sedimentation field-flow fractionation applied to the resolution and characterization of aggregates of colloidal particles. It is shown that a model colloidal system composed of aggregates having different numbers of “monodisperse” polymethylmethacrylate latex microspheres can be resolved into component clusters containing up to eight microspheres. The mechanism of peak broadening for the peaks corresponding to different-sized clusters is investigated in order to obtain cluster polydispersity and the resulting resolution between adjacent cluster peaks. The theoretical approach is based on the assumptions that the individual aggregates are formed randomly from the microsphere population and that the major peak broadening arises from cluster polydispersity. Equations for the polydispersity of the multiplets and for the resolution between adjacent peaks are derived. Experimental data on the peak resolution and plate height measurements are found to correlate well with theoretical predictions based on sample polydispersity.