General optical properties

AEROSIL^® offers far more than an attractive appearance:

• Transparency
• Smooth, glossy surfaces
• Matting of surfaces

RTV one-component silicone sealants are reinforced with AEROSIL^® fumed silica; they are usually pigmented but may also be highly transparent, glossy or matt

Special effects: matting of silicone surfaces

Matting of silicone sealants is of interest in certain application areas for safety reasons (to provide an anti-glare effect) as well as for esthetic purposes. In electronic LED displays, for example, matting suppresses disturbing reflectance of light. Conventional matting agents cannot be used in silicone sealants because their water content is too high. Moreover, the large quantities of these substances necessary to achieve a matting effect would adversely affect the mechanical properties. Evonik’s VP AEROPERL^® R 806/30 is a novel synthetic silica,developed specifically for RTV one-component silicone sealants, achieving significant matting even when used in small quantities.

Matting effect of surfaces

(A) Conventional sealant with AEROSIL^® products (glossy surface)
(B) Sealant with AEROSIL^® fumed silica and VP AEROPERL^® R 806/30 (matt surface)

AEROSIL® lets you keep things in view

Thanks to AEROSIL^® fumed silica, silicone rubber is colorless and highly transparent. This has resulted in the material being used in a wide range of applications on purely esthetic grounds. Silicone rubber can be pigmented to almost any color, but highly transparent formulations are also commercially available. These are used for medical applications, such as tubes and catheters, but are also preferred in products for daily use such as nipples for baby bottles and diving goggles because they allow visual checking.

The transparency of such formulations is controlled essentially by two factors: the particle size of the silica and the refractive index of the polymer or filler. AEROSIL^® grades such as AEROSIL^® 300 SP having a relatively high active surface area are especially suitable for highly transparent silicone systems. By modifying the fumed silica surface with silanes or silicones, the refractive index can be adjusted so that it is similar to that of silicone rubber, improving the transparency of the silicone system.

AEROSIL^® R 106 and AEROSIL^® R 812 S are examples of extremely hydrophobic materials that allow high-transparency products.