SILICA AEROGEL-POLYMER NANOCOMPOSITES AND NEW NANOPARTICLE SYNTHESES

Abstract

Aerogels are extremely high surface area, low density materials with applications including thermal and acoustic insulators, radiation detectors and cometary dust particle traps. However, their low density and aggregate structure makes them extremely fragile and practically impossible to machine or handle without breaking. This has led to the development of aerogel composites with enhanced mechanical properties through the addition of polymers or surface modifiers. To date, attempts to strengthen aerogels have come with significant increases in density and processing time. Here I will describe our search for a solution to these problems with our invention using methyl cyanoacrylate chemical vapor deposition (CVD) to strengthen silica, aminated silica and bridged polysilsesquioxane aerogels. This approach led to a strength improvement of the composites within hours and the strongest composite prepared had a 100x strength improvement over the precursor aerogel. We also developed the first approach to control the molecular weight of the polymers that reinforce silica aerogels using surface-initiated atom transfer radical polymerization (SI-ATRP). Although PMMA reinforcement of silica aerogels improved the mechanical properties, further strength improvements were achieved by cross-linking the grafted PMMA. Additionally, we developed the first silica aerogels reinforced with polyaniline nanofibers that were strong and electrically conductive. Reinforcing silica aerogels with polyaniline allowed them to be used as a sensor for the detection of protonating and deprotonating gaseous species. Finally we developed a new approach for the synthesis of silica and bridged polysilsesquioxane spheres using a surfactant free synthesis. This approach allowed for the first in-situ incorporation of base sensitive functionalities during the sol-gel polymerization.