Compounding Fumed Silicas into Polydimethylsiloxane: Bound Rubber and Final Aggregate Size

Area of Science:

• Materials Science
• Polymer Science
• Colloid Science

Background:

• Fumed silicas are widely used as reinforcing fillers in polymers.
• Understanding filler-polymer interactions is crucial for optimizing material properties.
• Polydimethylsiloxane (PDMS) is a versatile silicone polymer with diverse applications.

Purpose of the Study:

• To investigate the adsorption of PDMS onto fumed silicas during mechanical mixing.
• To examine the impact of mechanical mixing on silica aggregate size and PDMS molecular weight distribution.
• To correlate silica surface chemistry and polymer molecular weight with suspension properties.

Main Methods:

• Mechanical mixing of bulk PDMS with fumed silicas (untreated and chemically modified).
• Determination of bound rubber content using weight difference and carbon analysis.
• Analysis of silica aggregate size and PDMS molecular weight distribution post-mixing.

Main Results:

• Silica-PDMS suspensions exhibited varying degrees of dispersion or swelling based on filler concentration, silica surface chemistry, and PDMS molecular weight.
• Bound rubber content was quantified and compared to existing literature values.
• Final silica aggregate size remained consistent across different silica types after prolonged mechanical mixing.

Conclusions:

• Mechanical mixing significantly influences the dispersion and interaction of fumed silicas in PDMS.
• Silica surface chemistry and PDMS molecular weight are key factors governing adsorption and suspension behavior.
• The mechanical mixing process leads to a consistent final aggregate size, suggesting a saturation or equilibrium state is reached.