Silica Particles: Size and Colloidal Stability by Using the Litesizer 500

Silica is a widely used material that is abundant in nature (mostly as quartz) as well as in living organisms. Its diverse applications include paints and coatings as a thixotropic or thickening agent, and as an anti-settling agent. It is used in the microelectronics industry in chemical mechanical polishing (CMP). It is also used to clarify beer. In each application, the size of the silica nanoparticles plays a critical role.

For instance, the silica particles used for CMP must be small enough to avoid scratching the delicate silicon wafer, but large enough to remove unwanted materials quickly and cost-effectively. For the production of ceramic products, particle size is the most important parameter, and must be optimized for each product to achieve the desired physical and mechanical properties. Most ceramic products are manufactured by slip casting in a mould. Dispersion stability is also important because particles need to stay in suspension for deposition to occur evenly on the mould walls. The stability of a suspension is measured in terms of zeta potential, which reflects the strength of the repulsive interaction between particles in suspension. A zeta potential near the isoelectric point would result in particle aggregation because there would be insufficient repulsive force between particles. Thus, there is a need to measure both the particle size and the zeta potential of silica suspensions in order to properly analyze silica quality. Furthermore, for many applications, polymer additives such as polyethylene glycol (PEG) are often used to stabilize the particles and thereby reduce aggregation. PEG is known to bind to silica nanoparticles and has also been used as a plasticizer.

In this study, we measure the particle size and zeta potential of silica in suspension by using dynamic light scattering (DLS) and electrophoretic light scattering (ELS) with the Litesizer™ 500. We also investigate how particle size and zeta potential are affected by pH, and by the addition of polyethylene glycol (PEG) to the silica suspension.

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