Polyimide aerogels made using anhydride-capped oligomers from 4,4'-oxydianiline (ODA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) cross-linked with 1,3,5-tri(aminophenoxy)benzene (TAB) have been reported with very good mechanical properties but poor resistance to moisture. Replacing 50 mol % of the ODA with poly(propylene glycol)bis(2-aminopropyl ether) (PPG) with an average molecular weight of 230 g/mol in the oligomer backbone gives aerogels with water contact angles of 80°. The aerogels also absorb very little moisture on soaking in water. The aerogels also shrink less with increasing PPG concentration and therefore have significantly lower density and higher porosity than those made without PPG. Mechanical properties of the aerogels increased with increasing density, regardless of the polymer backbone. Brunauer-Emmett-Teller (BET) surface area of the aerogels studied ranged from 300 to 400 m/g, depending mainly on PPG concentration. The high moisture resistance makes them promising materials for substrates for lightweight antennas as well as insulation for a variety of applications.

Typical microcombustion-based power devices entail the use of catalyst to sustain combustion in less than millimeter scale channels. This work explores the use of several other candidate fuels for ~8 nm diameter Pt particle catalyzed combustion within 800 μm channel width cordierite substrates. The results demonstrate while commercial hydrocarbon fuels such as methane, propane, butane, and ethanol can be used to sustain catalytic combustion, room temperature ignition was only observed using methanol-air mixtures. Fuels, other than methanol, required preheating at temperatures >200°C, yet repeated catalytic cycling similar to methanol-air mixtures was demonstrated. Subsequently, a new reactor design was investigated to couple with thermoelectric generators. The modified reactor design enabled ignition of methanol-air mixtures at room temperature with the ability to achieve repeat catalytic cycles. Preliminary performance studies achieved a maximum temperature differenceΔTof 55°C with a flow rate of 800 mL/min. While the temperature difference indicates a respectable potential for power generation, reduced exhaust temperature and improved thermal management could significantly enhance the eventual device performance.