Optimal formulation and processes can maximize filled silicone material performance.

Silicones can be developed into fluids, gels, adhesives, elastomers, and resins designed with unique properties that make them ideal for specific application uses in the defense and aerospace industries. Silicones are most widely known for their ability to maintain elastomeric properties in extreme conditions, but an additional benefit of these materials is the ability to incorporate large amounts of fillers that can impart properties such as electrical and thermal conductivity, and radar-absorbing characteristics. Silicone materials appear in a wide variety of material compositions, and this broad range of material compositions makes silicone a viable option to endless numbers of optic applications.

Many powder fillers are currently added to silicone systems to achieve different properties (see table). Some of the most significant properties that fillers can add include thermal and electrical conductivity, thermal stability, color, and strength to the elastomer system. The chemical and physical properties of siloxane polymers allows for the incorporation of various fillers. The bond angles of the silicon-oxygen bonds create large amounts of free volume in silicone elastomers. This free volume, associated with the high compressibility found in silicones, bodes well for dispersions of fillers in silicone.

Reinforcement fillers are the most common fillers added to silicone elastomer systems used to improve mechanical properties, as filler particles reinforce an elastomer by reducing the mobility of the siloxane chains. The uniform distribution and the particle surface area available to make contact with the siloxane chains have the most influence on a reinforced elastomer’s physical properties.

Functional fillers impart properties uncharacteristic of polysiloxane elastomers like color, thermal conductivity, or electrical conductivity. The table shows a brief list of both reinforcing and functional fillers.