Degree Name

Master of Science (MS)

Semester of Degree Completion

2015

Thesis Director

Jonathan P. Blitz

Abstract

The goal of this research was to determine the effects of processing conditions on the morphology and surface chemistry of silica nanoparticle based cryogels. All processing conditions resulted in a change in morphology or surface chemistry compared to the starting material, CAB-O-SIL HS5 fumed silica. N2 adsorption isotherms were used to characterize surface area and pore size distributions of fumed silica and silica cryogels. TGA (thermogravimetric analysis) was performed on all samples in order to characterize the adsorbed water and hydroxyl group content of the silica surface. Solid state 29Si NMR was also used to evaluate surface chemistry of the cryogel samples. It was found that exposure of the silica surface to excess water during cryogel preparation results in a higher degree of hydroxylation than the bare, unprocessed silica. Freezing and freeze drying most prominently affect the morphological properties of the cryogel, such as bulk density and pore volume. Freeze drying can cause a high degree of variability in both bulk density and pore volume, which can override smaller effects on cryogel morphology caused by other processing parameters. The surface of silica heated to 650°C before cryogel processing was largely de-hydroxylated, and did not fully re-hydroxylate in the presence of water. When exposed to high pH (10) conditions, the surface area of a silica cryogel is reduced due to the increased solubility of silica in water at high pH. Overall, cryogel processing parameters result in significant changes from the starting material. Many processing parameters result in morphological changes, although surface chemistry has been shown to play an important role in determining the properties of all cryogel samples.

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