Synthesis of lightweight polymer-reinforced silica aerogels with improved mechanical and thermal insulation properties for space applications

Cross-linking of silica aerogels with organic polymers is an effective way to overcome their fragility and poor mechanical properties. It has also been shown that adjusting the nanoskeleton of silica aerogels using different silica precursors can lead to improved mechanical properties, mesoporosity and thermal conductivity. In this paper, the effect of the incorporation of 1,6-bis(trimethoxysilyl)hexane (BTMSH) and 1,4-bis(triethoxysilyl)-benzene (BTESB) into the underlying silica structure of tri-methacrylate crosslinked silica aerogels is examined. In order to attain a simple, cost and time effective procedure, the sol-gel process and addition of organic monomers are performed in one single step. The effect of the amount of silicon derived from alkyl-linked and aryl-linked bis-silane precursors as well as the effect of the cross-linker concentration on the mechanical strength, thermal conductivity, porosity and other properties of the synthesized aerogels are studied. Different reinforced silica aerogels with density range from 0.13 to 0.39 g cm(-3), compression strength from 11 to 400 kPa and thermal conductivity of 0.039-0.093 W m(-1) K-1 were obtained. The cross-linked aerogels made by replacing 5-10 mol% of total silicon by BTESB showed a drastic improvement in their surface area and thermal insulation properties along with an increase in the mechanical strength. The surface area and thermal insulation improvements obtained for aryl-bridged polysiloxanes were attributed to the aryl spacer within the aerogels body, which leads to aerogel with high extent of porosity or pore volume when compared to the alkyl-bridged polysiloxanes. Therefore, for the first time we were able to show the dependency of thermal conductivity values on the silica structure by proper designing the mesoporosity of the resulting aerogels. (C) 2014 Elsevier Inc. All rights reserved.