RESUMEN
In this study, in situ infrared spectroscopy techniques and thermogravimetric analysis coupled with mass spectrometry (TGA-MS) are employed to characterize the reactivity of the ionic liquid, 1-butyl-3-methylimidazolium dicyanoborohydride (BMIM+DCBH-), in comparison to the well-characterized 1-butyl-3-methylimidazolium dicyanamide (BMIM+DCA-) ionic liquid. TGA measurements determined the enthalpy of vaporization (ΔHvap) to be 112.7 ± 12.3 kJ/mol at 298 K. A rapid scan Fourier transform infrared spectrometer was used to obtain vibrational information useful in tracking the appearance and disappearance of species in the hypergolic reactions of BMIM+DCBH- and BMIM+DCA- with white fuming nitric acid (WFNA) and in the thermal decomposition of these energetic ionic liquids. Attenuated total reflectance measurements recorded the infrared spectra of the reactant sample (BMIM+DCBH-) and the liquid reaction products after reacting with WFNA. Computational chemistry efforts, aided by the experimental results, were used to propose key reaction pathways leading to the hypergolic ignition of BMIM+DCBH- + WFNA. Experimental results indicate that the hypergolic reaction of BMIM+DCBH- with WFNA generates both common and unique intermediates as compared to previous BMIM+DCA- + WFNA investigations: nitrous oxide was generated during both hypergolic reactions indicating that it may play a crucial role in the hypergolic ignition process, NO2 was generated in significantly higher concentrations for BMIM+DCBH- than for BMIM+DCA-, CO2 was only generated for BMIM+DCA-, and HCN was only generated during thermal decomposition and hypergolic ignition of BMIM+DCBH-.
RESUMEN
Hydrogen-bonding-induced ordered assembly of poly(3-alkylthiophene)s derivatives bearing carboxylic acid groups has been investigated from diluted and concentrated solutions to solid films using ultraviolet-visible absorption spectroscopy, polarized optical microscopy, and four-point probe conductivity measurements. In dilute solutions, the polymer undergoes a spontaneous structural transition from disordered coil-like to ordered rodlike conformations, which is evidenced by time-dependent chromism. Many factors such as alkyl-chain length, types of solvents, and temperature are studied to understand the assembly behavior. Transition kinetics of the assembly process reveals a universal second-order rate law, indicating an intermolecular origin due to hydrogen bonding. When more concentrated, hydrogen bonding drives nematic liquid-crystalline gelation above a critical concentration and the gels are thermally reversible. Under an appropriate balance of mechanical and thermal stresses, uniform liquid-crystalline monodomains are obtained through the application of a mechanical shear force. The dried films made from the sheared solutions display both optical and electrical anisotropies, with a more than 200% increase in charge transport parallel to the direction of shear as opposed to that in the perpendicular one.