Stephane F. Rouanet

Use of surface treated aerogels derived from various silica precursors in translucent insulation panels

Many translucent industrial insulation applications require optimization of both the thermal and optical properties. Currently, the thermal performance witnessed in todays products often limits the amount of available area which can be designated for translucent panels. For example, translucent wall panels for passive lighting systems must provide both adequate light transmission as well as sufficient thermal insulation. In granular fill systems, these demands can sometimes work against each other since thermal performance will improve as the panel thickness is increased but light transmission will decrease accordingly. In contrast, the optical properties can be significantly enhanced by careful control of the particle size and size distribution. This in turn impacts the thermal resistance since spaces between the particles act as large pores that dominate the heat transfer. We have investigated aerogel materials derived from commercially viable silica sources. Results indicate that depending on the silica precursor, particle size distribution, and control over other processing conditions, the optical transparency can be varied from 25% to 80% in a 20 mm layer. Within these same constraints, we have found the thermal conductivity can be varied from 0.0140 to 0.0210 W/m K. This ability to tailor the optical and thermal characteristics, coupled with superior thermal properties of aerogel, may enable more widespread acceptance.

The use of vinyl functional aerogels for reinforcement of silicone rubbers

Silane-treated silicate-based aerogels are excellent reinforcing fillers for silicone rubbers. The physical properties of the aerogel filler can be readily altered by controlling the properties of the hydrogel, and the vinyl functionality of the aerogel surface can be easily and precisely controlled in the silylation step of the aerogel manufacturing process. By changing the vinyl content on the surface of the aerogel, the physical properties of the rubber can be markedly changed without the use of any in situ treating agents during compounding or alteration in the formulation. The silicone rubber hardness and modulus of elasticity exhibit a sensitive response to the vinyl content, while the plasticity of the uncured base shows no effect of vinyl loading. In contrast, the viscosity (plasticity) of the uncured rubber is a strong function of the aerogel surface area, whereas the rubber modulus and strength are only slightly affected by particle properties such as surface area. In addition, the high porosity of aerogels allows for good fracture characteristics and dispersion of the filler during compounding, while the large pore size provides good accessibility to and utilization of the vinyl sites within the porous structure. The ability to easily control the aerogel structure, to completely hydrophobize the silica surface, and to precisely control the vinyl loading make aerogels a potentially useful new particle for rubber reinforcement. A brief summary of the treatment chemistry and the vinyl surface chemistry is also presented in the paper.