ABSTRACT
Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551
Normal FFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551
Steric FFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553
Experimental Details . . . . . . . . . . . . . . . . . . . . . . . . 553
Sedimentation FFF . . . . . . . . . . . . . . . . . . . . . . . . 553
Flow FFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
Thermal FFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
Standards and Samples . . . . . . . . . . . . . . . . . . . . 554
Scanning Electron Microscopy . . . . . . . . . . . . . . 555
Transmission Electron Microscopy . . . . . . . . . . . 556
Data Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 556
Results and Discussion . . . . . . . . . . . . . . . . . . . . . . 556
Ludox Colloidal Silica . . . . . . . . . . . . . . . . . . . . . 556
Monospher Colloidal Silica . . . . . . . . . . . . . . . . . 558
Nyacol Colloidal Silica . . . . . . . . . . . . . . . . . . . . 558
Cab-O-Sil Fumed Silica . . . . . . . . . . . . . . . . . . . 560
Chromatographic Silica . . . . . . . . . . . . . . . . . . . . 561
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . 563
List of Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
Particle-size and mass distribution curves, along with information on particle porosity, density, shape, and
aggregation, can be obtained for submicrometer-and supramicrometer-size silica materials suspended
in either aqueous or nonaqueous media by field-flow fractionation (FFF). Narrow fractions can readily
be collected for confirmation or further characterization by microscopy and other means. Among the
silicas examined were different types of colloidal microspheres, fumed silica, and various chromatographic
supports. Size distribution curves for aqueous silica suspensions were obtained by both sedimentation FFF
and flow FFF and for nonaqueous suspensions by thermal FFF. Populations of aggregates and oversized
particles were isolated and identified in some samples. The capability of FFF to achieve the high-resolution
fractionation of silica is confirmed by the collection of fractions and their examination by electron
microscopy.