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A common question from formulators is:
“Why is this fumed silica so difficult to disperse?”
It is tempting to assume that poor dispersion automatically means the silica quality is poor.
But dispersion is influenced by several factors, including the silica itself, the formulation and the mixing process.
Before changing the material, it is useful to check the complete system.
Fumed silica consists of very fine particles that form aggregates and larger agglomerated structures.
Because of its high specific surface area and particle interactions, it does not behave like a conventional coarse mineral filler.
This is one reason why fumed silica requires appropriate incorporation and dispersion conditions.
How silica is introduced into the formulation can affect processing.
Adding a large amount too quickly may make wetting and incorporation more difficult.
Depending on the formulation and equipment, controlled addition may help the silica become incorporated more consistently.
The appropriate sequence should be determined according to the actual process.
Mixing equipment matters.
Different production systems can provide very different levels of shear and circulation.
Useful information includes:
If a laboratory test and production batch use very different equipment, their dispersion results may also differ.
The viscosity and chemistry of the base polymer or resin influence how easily the silica can be incorporated.
A silica grade that disperses well in one system may behave differently in another.
This is why a supplier should know whether the customer is working with:
Increasing silica dosage can significantly change viscosity during mixing.
At higher loading, the existing equipment or mixing procedure may no longer provide the same incorporation behavior.
Therefore, when a dispersion problem appears after changing dosage, both the material and the processing conditions should be reviewed.
Yes.
Hydrophilic and hydrophobic fumed silica have different surface characteristics, which can influence their interaction with the formulation.
For example, IOTA HL7200 is a hydrophilic fumed silica used in silicone materials, coatings, adhesives and sealants.
IOTA HL7200 Hydrophilic Fumed Silica
IOTA also provides hydrophobic fumed silica grades for applications where surface-treated silica is more appropriate.
A change from one surface type to another should therefore be evaluated in the actual formulation rather than treated as a simple specification replacement.
Not necessarily. Silica characteristics, formulation viscosity, addition sequence and mixing conditions can all influence dispersion.
The appropriate addition method depends on the formulation and equipment. Controlled incorporation may be useful in some systems.
Not automatically. Equipment, formulation, temperature, mixing time and silica characteristics should be considered together.
Yes. Their different surface characteristics can affect interaction with the formulation.
Provide the formulation type, current silica grade and dosage, mixer type, mixing sequence, mixing conditions and the specific dispersion problem observed.
When fumed silica is difficult to disperse, evaluate the material, formulation and process together before assuming that changing the silica grade alone will solve the problem.
