Successful Use of Fumed Silica in Liquid Systems

Successful Use of Fumed Silica in Liquid Systems

Fumed silica, both hydrophilic and hydrophobic, plays an essential role in various liquid systems by contributing to viscosity control, anti-sag, anti-settling effects, and enhancing the overall rheological properties. For optimal results across all fumed silica grades, certain key conditions must be followed.

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• Determine the optimal addition level
• Utilize the appropriate dispersion methods:
  • Equipment and design features
  • Considerations of tip speed
  • Shearing time requirements
  • Managing temperature build-up
  • Sequence of component addition
  • Comparing masterbatch versus direct addition
  • Grind values against dispersion efficiency
  • Averting under or over shearing
• Finalizing the formulation

Determining the Optimization Level

In liquid formulations ranging from non-polar to semi-polar contexts, hydrophilic AEROSIL brands such as 130, 200, 300, and 380 serve as reliable agents for rheological advancements. In semi-polar to polar systems, hydrophobic grades such as AEROSIL R972, R974, R812, R812S, R202, and R805 provide similar benefits, albeit with slightly reduced efficiency compared to hydrophilic options. Their additional properties, including water resistance, improved leveling, and suspension of pigment manage viscosity without significant increase while enhancing corrosion resistance.

Typically, the load levels in coatings and ink formulations are kept low, generally under 1.0% by weight of the overall system, as a starting measure. For properties relating to anti-settling, levels may be as high as 1.5% if accompanied by considerable quantities of additional pigments and fillers. Adhesive and sealant applications typically warrant higher proportions, around 4-8%, due to their thicker viscosity demands. Ultimately, the precise percentage is contingent upon several factors, such as initial viscosity, desired conditions, storage stability, and formulation polarity, determined through systematic trials.

Employing Effective Dispersion Techniques

Achieving optimal efficiency from fumed silica necessitates the use of adequate dispersion techniques. Standard low shear mixing methods involving propellers or stirring blades often fall short for all AEROSIL grades, leading to inconsistency in thickening performance across batches. When employing low shear techniques, inadequate energy is expended, resulting in a need for higher silica quantities, poor grind behavior, and reduced stability.

Conversely, high shear dispersion (HSD) with aggressive saw-tooth blades is essential, particularly for AEROSIL grades with surface areas between 90-200. For high surface area silica grades, more energy-intensive equipment may be necessary to achieve desirable dispersion levels, and optimal tip speeds should exceed 30 ft/sec for industrial applications.

The ratio of the blade to the vessel is also crucial; maintaining a 1:2-1:3 ratio helps produce a robust vortex for efficient mixing—whereas a 1:4 ratio results in materials clinging to the tank’s walls, hindering optimal wetting and mixing efficiency. Regular maintenance of blades alongside monitoring equipment RPM and torque ensures consistent processing and efficiency.

For the highest thickening efficiency and clarity, high-intensity mills and sand mills are recommended for high surface area AEROSIL. Additionally, minimizing dispersion length helps avoid excessive temperatures that could lead to over-dispersion and reduced thixotropic properties. Once wetting occurs, ensure the subsequent mixing speeds increase to promote optimal dispersion.

Lastly, the sequence of fumed silica addition is vital. Testing indicates that fumed silica should follow the introduction of the resin to promote effective wetting and dispersion. In particular, systems requiring hydrophobic grades should ensure that fumed silica is introduced into the vehicle without water to prevent complications during dispersion.

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