Electronic and Structural Consequences of n-Doping: Bithiazole Oligomers and Partially Reduced Bithiazolium Cations

N-methylated-poly(diakyl-bithiazoles), NPABTs, can be reduced to give reasonably stable n-doped polymers. In order to understand the changes in the electronic structure and polymer conformations upon reductive doping of NPABTs, a series of oligomers of increasing length was studied by self-consistent field (AM1) and configuration interaction (ZINDO/S) calculations. Large red shifts in the optical transitions are predicted upon n-doping, along with significant planarization of chain segments. Full planarization was not realized for n-doped materials, however, as a variety of localized units were observed

Method for Thermal Management Through Use of Ammonium Carbamate

Ammonium carbamate-based methods and systems for management of thermal loads, particularly low-quality, high-flux thermal loads. The increase in temperature in heat sensitive devices is mitigated by the endothermic decomposition of ammonium carbamate into carbon dioxide and ammonia gases. This process has an energy density an order of magnitude greater than conventional thermal management materials and is particularly useful for temperatures between 20° C. and 100° C. Systems incorporating ammonium carbamate may be controlled by regulating the fluid flow, overhead pressure, temperature, or combinations thereof

The Use of Ammonium Carbamate as a High Energy Density Thermal Energy Storage Material

Phase change materials (PCMs) often have higher specific energy storage capacities at elevated temperatures. Thermal management (TM) systems capable of handling high heat fluxes in the temperature range from 20–100°C are necessary but lacking. State of the art PCMs in this temperature range are usually paraffin waxes with energy densities on the order of a few hundred kJ/kg or ice slurries with energy densities of the same magnitude. However, for applications where system weight and size are limited, it is necessary to improve this energy density by at least an order of magnitude. The compound ammonium carbamate, [NH4][H2NCOO], is a solid formed from the reaction of ammonia and carbon dioxide which endothermically decomposes back to CO2 and NH3 in the temperature range 20-100°C with an enthalpy of decomposition of ∼2,000 kJ/kg. Various methods to use this material for TM of low-grade, high-flux heat have been evaluated including: bare powder, thermally conductive carbon foams, thermally conductive metal foams, hydrocarbon based slurries, and a slurry in ethylene glycol or propylene glycol. A slurry in glycol is a promising system medium for enhancing heat and mass transfer for TM. Progress on material and system characterization is reported

CIS-DEFECTS IN TRANS-POLYENES

Author Institution: Air Force Research LaboratoryAll trans-polyenes have received tremendous experimental and theoretical attention because of their importance to vision and photosynthesis as well as conductive and semiconductive electronic applications. Numerous examples exist of cis-linkages contained in an otherwise all trans-polyene unit, such as the cis-trans isomerization associated with the vision process or the cis-polyacetylene formed initially in the Shirakawa synthesis of trans-polyacetylene. Though such cis-structures can have significant impact on optical, electronic, and nonlinear optical properties, such defects have received only scant attention. In this work, we report the results of ab initio calculations on the structure and properties of cis-defects embedded within all-trans-polyene units

STABILITY OF NANOPOLYACETYLENE AT LASER EXCITATION OF RESONANT AND NON-RESONANT RAMAN SCATTERING

Author Institution: Air Force Research Laboratory, Materials and Manufacturing DirectorateWe present resonant and non-resonant Raman scattering experiments for free-standing nanopolyacetylene (NPA) films in which long-duration irradiation by high intensity laser beams does not lead to film destruction. NPA films with thickness from 0,005 to 1 mm consist of 0.5-2 percents polyacetylene nanoparticles by weight having diameter from 15 to 30 nm dispersed in a matrix of poly (vinyl butyral). The calculated energy absorbed from the laser irradiation exceeds that required for thermal destruction of NPA films by a factor of 10-1000. These results allow one to suppose that laser irradiation leads to excitation of coherent vibrations in trans-NPA. Coherent vibrations are characterized by non-Boltzmann energy distributions, and increased absorption of the laser energy from Raman scattering of trans-NPA leads to an increase in the amplitudes, but not frequencies, of the coherent vibrations. Thus NPA can absorb much more coherent light than noncoherent light. Growth of coherent light absorption is accompanied by only very weak heating of NPA films. Questions remain regarding the energy balance for the irradiation experiments, but one possibility is that NPA films undergo an energy exchange between nanoparticles, which are irradiated with those that are not irradiated