Patricia S. Sawyer

Surfactant-templated silica aerogels

By combining the molecular silica precursor tetramethoxysilane (TMOS) with an alkaline, micellar, water: methanol solution, we form surfactant-templated silica gel (STSG) monoliths. The wet monoliths can be exchanged with ethanol and then supercritically extracted with carbon dioxide to produce surfactant-templated silica aerogels (STSAs). STSAs represent a new class of aerogels that are composed of aggregated submicron porous particles that have tunable intraparticle nanoporosity. STSAs catalyzed with NH4OH experience no measurable shrinkage upon extraction and have bulk densities less than ~0.15 g/cc. The STSAs can then be calcined to remove the remainder of the surfactant. The calcination process leads to minimal shrinkage (<8%), high surface area (~700 m2/g), uncracked monoliths with hierarchical inter- and intraparticle porosities, and bulk densities less than 0.08 g/cc. We use XRD, SAXS, SEM. 29Si NMR. and N2 Sorption to characterize the structure and porosity of these novel aerogels.

High temperature polymer dielectrics from the ring opening metathesis polymerization (ROMP)

Recently much research has focused on the development of new polymer dielectric materials to fabricate capacitors for use in the inverters of next generation hybrid electric vehicles (HEV). The capacitors used in HEVs inverters will be required to operate at 150 °C, 600V, and have an energy density of 0.9 J/cm3. Polymer based thin film capacitors are ideal for this application due to their relatively high energy density, low cost, and high dielectric breakdown strength. We have polymerized several ring strained monomers using ring opening metathesis polymerization (ROMP) and have identified a promising polymer system based on N-Phenyl-7-oxanorbornene-5,6-dicarboximide (PhONDI). Several of its copolymers with norbornene have been evaluated for possible use as next generation high temperature polymer dielectrics in thin film capacitors. The copolymers were cast into thin films and Au electrodes were deposited on the polymer film. The electrical properties were evaluated as a function of temperature. The polymer system exhibited very good high temperature dielectric properties and is potentially useful as a high temperature capacitor dielectric.

Parylene C Aging Studies

Parylene C is used in a device because of its conformable deposition and other advantages. Techniques to study Parylene C aging were developed, and %22lessons learned%22 that could be utilized for future studies are the result of this initial study. Differential Scanning Calorimetry yielded temperature ranges for Parylene C aging as well as post-deposition treatment. Post-deposition techniques are suggested to improve Parylene C performance. Sample preparation was critical to aging regimen. Short-term (~40 days) aging experiments with free standing and ceramic-supported Parylene C films highlighted %22lessons learned%22 which stressed further investigations in order to refine sample preparation (film thickness, single sided uniform coating, machine versus laser cutting, annealing time, temperature) and testing issues (%22necking%22) for robust accelerated aging of Parylene C.

Control of Pore Size in Epoxy Systems

Both conventional and combinatorial approaches were used to study the pore formation process in epoxy based polymer systems. Sandia National Laboratories conducted the initial work and collaborated with North Dakota State University (NDSU) using a combinatorial research approach to produce a library of novel monomers and crosslinkers capable of forming porous polymers. The library was screened to determine the physical factors that control porosity, such as porogen loading, polymer-porogen interactions, and polymer crosslink density. We have identified the physical and chemical factors that control the average porosity, pore size, and pore size distribution within epoxy based systems.

Development of a Chemiresistor Sensor for Polypropylene Degradation Products

This paper presents the development of a sensor to detect the oxidative and radiation induced degradation of polypropylene. Recently we have examined the use of crosslinked assemblies of nanoparticles as a chemiresistor-type sensor for the degradation products. We have developed a simple method that uses a siloxane matrix to fabricate a chemiresistor-type sensor that minimizes the swelling transduction mechanism while optimizing the change in dielectric response. These sensors were exposed with the use of a gas chromatography system to three previously identified polypropylene degradation products including 4-methyl-2-pentanone, acetone, and 2-pentanone. The limits of detection 210 ppb for 4-methy-2-pentanone, 575 ppb for 2-pentanone, and the LoD was unable to be determined for acetone due to incomplete separation from the carbon disulfide carrier.