Text

theses

Sol-gel processing is an integral tool in developing inorganic-organic nanocomposite materials from wet chemistry techniques. By controlling the hydrolysis and condensation of various alkoxysilane precursors, tunable hybrid structures and properties can be achieved. A special class of sol-gel nanocomposites are so called “melting gels”, which thermally cure like an epoxy, but produce organically functionalized silicates. These melting gels are noted for their adhesion, hermeticity, chemical stability, and thermal stability.

This thesis focuses on the synthesis and characterization of new wax-melting gel composites. Both paraffin and microcrystalline waxes were successfully dispersed as microparticles in a melting gel matrix through in-situ emulsification with a silicone-based surfactant. “Par-gels” and “Micro-gels” were synthesized with between 5.2 and 17.6 vol% wax. The samples were characterized using profilometry, optical microscopy, and SEM analysis. Additionally, the dielectric behavior of these wax-gels was evaluated in the RF spectral range (~1-1000 kHz) and measured as a function of cumulative thermal history.

It was found that the emulsion stability of Par-gels is greater than that of Micro-gels. Specifically, Micro-gels contained internal pools of wax and surface segregated wax islands, while Par-gels showed more uniform mixing. Using image analysis with SEM and optical microscopy to resolve particle sizes, the distributions were best fitted with a Gamma distribution for particle sizes between ~0.1-300 microns. Micro-gels exhibited larger median particle sizes than Par-gels, but both showed that the majority of their wax content was microparticles between ~5-50 microns. Additionally, it was found that the dielectric properties were insensitive to wax content from 0-17.6 vol%. In addition, one week of sustained thermal treatments at ~175°C caused the dielectric behavior of all samples to converge into a narrow range. These thermal aging effects suggest that melting gels continue to undergo structural changes beyond the recommended consolidation conditions.

ETD_10675

doi:10.7282/t3-vkw4-jp55

M.S.

Includes bibliographical references

ETD graduate

The author owns the copyright to this work.