Colloidal silicas are typically aqueous suspensions in the range of 30 – 500 nm in diameter. They are usually stabilized electrostatically and have densities in the range of 2.1 to 2.3 g/cm3. Applications for colloidal silicas include fillers, binders, abrasives, catalysts, and absorbants.
Most size measurements of colloidal silica are performed using dynamic light scattering (DLS) instruments such as the SZ-100 Nanoparticle Analyzer. The LA-960 Laser Diffraction Analyzer can uniquely measure down to the 30 nm size range, so this laser diffraction instrument is also an option for such tests.
TEM image of colloidal silica
Colloidal silica can also be used as a reference material for both particle size and zeta potential. Ludox TM silica is a well known and characterized colloidal material that has been studied using various particle size analysis techniques including acoustic spectroscopy, laser diffraction and dynamic light scattering. The results from these studies indicate that Ludox TM silica is an appropriate sample to use as a reference material for size and/or zeta potential.
In the EU the Institute for Reference Materials and Measurements (IRMM) has released two colloidal silica reference materials; ERM-FD100 and ERM-FD304. These samples have nominal particle sizes of 20 and 40 nm and include a reference zeta potential value as additional material information.
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