Carlos F. R. A. C. Lima

Abstract This work reports a comprehensive experimental evaluation of the solid-liquid-gas phase equilibria for five representative phenylene-thiophene co-oligomers (3-ring aromatic compounds having both phenyl and thienyl units). The melting temperatures and corresponding standard molar enthalpies and entropies of fusion were measured by differential scanning calorimetry. The equilibrium vapor pressures of the crystalline solids as a function of temperature were measured by a combined Knudsen/quartz-crystal effusion method, with the consequent derivation of the standard molar enthalpies, entropies, and Gibbs energies of sublimation. The thermodynamic properties of vaporization were estimated from the fusion and sublimation data. The results were analyzed together with the literature data for the corresponding phenylene and thiophene homo-oligomers. The thermodynamic properties of fusion and sublimation exhibited a dependence on ring identity and position that cannot be adequately described by a simple group additivity reasoning. The plot of the Gibbs energy of sublimation as a function of the number of thienyl rings in the co-oligomer showed the existence of two series. Terminal 3-thienyl rings and a linear molecular shape were found to be consistent factors contributing to the stabilization of the crystal phase. The higher melting temperatures and lower volatilities of crystalline 3-thienyl compounds were tentatively explained by the ability of these rings to maximize intermolecular C-H & BULL;& BULL;& BULL;pi interactions independently of the sulfur position. The optical energy gaps, as measured by UV-vis in solution, were found to lie within the values for typical organic semiconductors (< 4 eV) and to decrease for co-oligomers containing more 2-thienyl units, following the increased ring-ring planarity of the molecules. The surface morphology of vapor-deposited thin films suggests a stronger tendency of the co-oligomers, if compared to their corresponding homo-oligomers p-terphenyl and terthiophene, to form less amorphous films.

Abstract We report a study on the energetics and structural properties of gallic (1) and ellagic (2) acids. The experimental values of standard enthalpy of formation in solid state at 298.15 K, Delta H-f(m)0 (cd) of 1 as (-985.0 +/- 2.9 kJ.mol(-1)) and 2 as (-1377.9 +/- 4.7 kJ.mol(-1)) have been determined. The vapour pressure of 1 have been measure by Knudsen effusion methodology and the derived enthalpy of sublimation, Delta H-g(cd)m(0). was combined with the Delta H-f(m)0 (cd) in order to derive its gas-phase enthalpy of formation, Delta(f) H-m(0)(1,g) = -835.7 +/- 4.0 kJ.mol(-1). Quantum chemical calculations, at DFT (M05-2X) and composite ab initio Gn (n = 3, 4) levels of theory, provided the consistency of the experimental results and a plausible estimation of Delta H-f(m)0 (g) of 2 as (-1128.6 +/- 6.4 kJ.mol(-1)), which was deduced from the isodesmic-reactions methodology. (C) 2018 Published by Elsevier Ltd.

Abstract This work aims to provide reliable heat capacities for ethylene glycol and selected oligo(ethylene glycol)s (diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, and hexaethylene glycol), which are industrially important chemicals produced on a large scale. Besides, new data extend the database needed for a better understanding of complex behavior of compounds capable of forming hydrogen bonds. Isobaric heat capacities of ethylene glycols were measured with a Tian-Calvet-type calorimeter in the temperature range of 260 to 358 K. The phase behavior was investigated with a heat-flux differential scanning calorimeter. A simple additive estimation method for liquid heat capacity of oligo(ethylene glycol)s was developed and tested through comparison with newly measured liquid heat capacities of polyethylene glycols 400 and 600.

Abstract This paper reports thermodynamic properties of phase transitions of 2,4,6-trichloro and 2,4,6-tribromo anisoles and of 2,4,6-tribromophenol. The vapor pressures of both crystalline and liquid phases (including supercooled liquid) of the three compounds were measured, respectively, in the temperature ranges T = (297.1 to 368.3) K, T = (330.7 to 391.7) K, and T = (336.5 to 401.7) K, using a static method based on capacitance diaphragm manometers. Moreover, the sublimation vapor pressures of 2,4,6-tribromophenol were also measured in the temperature interval (307.2 to 329.2) K, using a Knudsen mass-loss effusion technique. The standard molar enthalpies, entropies, and Gibbs energies of sublimation and of vaporization, at reference temperatures, were derived from the experimental results as well as the (p,T) values of the triple point of each compound. The temperatures and molar enthalpies of fusion of the three benzene derivatives were determined using differential scanning calorimetry and were compared with the values derived indirectly from the vapor pressure measurements. The thermodynamic results were discussed together with the available literature data for 2,4,6-trichlorophenol. To help rationalize the phase behavior of these substances, the crystallographic structure of 2,4,6-tribromophenol was determined by single crystal X-ray diffraction.

Abstract Oxidative treatment of Multi-Walled Carbon Nanotubes (MWCNT's) was done by chemical functionalization by using the mixture acid, which is a mixture of sulfuric acid (H2SO4) and nitric acid (HNO3). Functionalization was governed by four parameters namely mixture acid concentration, temperature(T), time of heating(t) and the amount of MWCNTs used. After functionalization, functionalized MWCNT's were then diluted in dimethylformamide (DMF) to analyse the percentage of soluble MWCNT's. Also, by increasing the time of functionalization, it was observed that overall yield decreases but the percentage of functionalized product inside the yield quantity remains the same. Material characterization was also carried out at several steps to validate this theory. Chemical functionalization of MWCNT's is generally significant for the manufacturing of polymerbased nanocomposites. Oxidative treatment enhances the dispersion and interfacial bonding within the epoxy matrix. In this research work, a bio-based epoxy resin was selected for the manufacturing of nanocomposite samples with various concentrations of pristine and functionalized MWCNTs. Mechanical and electrical characterization was finally carried out to increase the knowledge on the interaction of MWCNT's with the selected green epoxy matrix system and their influence on the original properties of the resin. (C) 2019 The Authors. Published by Elsevier B.V.