AbstractsEngineering

Two novel techniques for spectroscopically studying materials under static and shock compression are described. The first known spectra of self-assembled organic monolayers under static pressure up to 10 GPa were obtained by the novel combination of surface-enhanced Raman scattering spectroscopy with diamond anvil cell technology. The samples used were benzenethiol (BT) and benzene methane thiol (BMT) adsorbed onto photonic substrates composed of silver films over polystyrene nanospheres. Results indicated that the thiols were mobile, not fixed, on the silver surface. Also reported is an application of this technique in which the high pressure vibrational response of an energetic material simulant is characterized. Second, a technique to simultaneously monitor the global and local responses of shocked materials with mesoscale inhomogeneities is discussed, using a dye (rhodamine 640) embedded in a polymer matrix (poly(methyl-methacrylate)) shocked to 15 GPa as a model system. The dye/polymer thin film was shocked using simplified laser-driven flyer plates, also described here. The local dynamics were probed using fluorescence emission of the dye, and the global dynamics were probed with a photon Doppler velocimeter. The results indicated that within the 8-15 ns duration of the imparted shock, the polymer was not able to fully compress and reach its highest density, which is implied by the leveling off of the dye fluorescence redshift with applied pressure over 7 GPa. ???