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.