Publications

Abstract Aqueous micellar two-phase systems (AMTPS) hold a large potential for cloud point extraction of biomolecules but are yet poorly studied and characterized, with few phase diagrams reported for these systems, hence limiting their use in extraction processes. This work reports a systematic investigation of the effect of different surface-active ionic liquids (SAILs) covering a wide range of molecular properties upon the clouding behavior of three nonionic Tergitol surfactants. Two different effects of the SAILs on the cloud points and mixed micelle size have been observed: ILs with a more hydrophilic character and lower critical packing parameter (CPP < 1/2) lead to the formation of smaller micelles and concomitantly increase the cloud points; in contrast, ILs with a more hydrophobic character and higher CPP (CPP >= 1) induce significant micellar growth and a decrease in the cloud points. The latter effect is particularly interesting and unusual for it was accepted that cloud point reduction is only induced by inorganic salts. The effects of nonionic surfactant concentration, SAIL concentration, pH, and micelle zeta potential are also studied and rationalized.

Abstract Numerous reports have shown that the self assembling properties of 12-s-12 bis(quaternary ammonium) gemini surfactants in aqueous solution are significantly influenced by s, the number of methylene groups in the covalent spacer. However, the role played by s on the phase behavior of the single compounds has not been investigated in a similarly systematic way. Here, we report on the thermotropic phase behavior of the anhydrous compounds with s = 2-6, 8, 10, and 12, resorting to differential scanning calorimetry (DSC), polarized light microscopy (PLM), and Xray diffraction (XRD). All of the compounds show a stepwise melting behavior, decomposing at 200 degrees C. As the spacer length increases, nonmonotonic trends are observed for the thermodynamic parameters of the thermotropic phase transitions, mesophase formation, and solid-state door spacings. In particular, the number and type of mesophases (ordered smectic phases and/or fluid smectic liquid crystals) depend critically on s. Further, upon heating molecules with s < 8 decompose before the liquid phase, while those with long spacers, s = 8-12, reach the isotropization (clearing) temperature, hence forming both ionic liquid crystals and ionic liquid phases. We demonstrate that the melting behavior and type of ionic mesophases formed by gemini molecules can be usefully manipulated by a simple structural parameter like the length of the covalent linker.

Abstract New polymer electrolytes (PEs), potentially interesting for solid-state electrochemical devices applications, were synthesized by a solvent casting method using pectin and ionic liquid (IL) N,N,N-trimethyl-N-(2-hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide ([N-1 1 1 2(OH)] [NTf2]. The resulting electrolytes besides being moderately homogenous and thermally stable below 155 degrees C, they also exhibited good mechanical properties. The SPE membranes were analyzed by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and complex impedance spectroscopy.

Abstract This work presents a comprehensive experimental and computational study of the thermodynamic properties of fluorene-2-carboxaldehyde. The crystal vapour pressures of this compound were measured between (335.16 and 355.09) K, using the Knudsen mass-loss effusion method. From these results the standard molar enthalpies, entropies and Gibbs energies of sublimation were derived. The standard molar enthalpy of formation in the crystalline phase at the temperature 298.15 K was derived from the standard molar energy of combustion, determined from combustion calorimetry measurements. This result was combined with the enthalpy of sublimation yielding the standard molar enthalpy of formation in the gaseous phase at T = 298.15 K, that was also derived from a computational study at the G3 and G4 levels. Theoretical calculations were also used to calculate heat capacity and entropy results in the gaseous phase. The enthalpy and temperature of fusion were determined from DSC experiments. From the thermodynamic properties of fusion and sublimation, those of vaporization were derived. The thermodynamic stability of fluorene-2-carboxaldehyde in the crystalline and gaseous phases was evaluated determining the standard Gibbs energies of formation, at the temperature 298.15 K, and compared with the ones reported in the literature for fluorene. (C) 2017 Elsevier Ltd.

Abstract In this work, several simple new equations for predicting important environmental mobility properties, at T = 298.15 K, were derived for halogenated benzenes: standard Gibbs energy of hydration, aqueous solubility, octanol-water partition coefficients, and Henry's law constants. A discussion on our previous estimates of other related properties (standard Gibbs energy and vapor pressure of sublimation and of vaporization) and their relation with entropy of fusion is also presented. As we aimed to estimate these properties for any of the ca. 1500 halogenated benzenes that may exist theoretically, an equation for estimating the temperature of fusion was also derived, since some of the proposed predictive equations (solubility of solids and Gibbs energy of sublimation) require its knowledge. For the other estimated properties just the number of each halogen that replaces hydrogen atoms in the halogenated benzene is needed. It was found that the coefficients that multiply the number of halogen atoms in the predictive equations vary linearly with the volume of the halogen atom.

Abstract This paper reports experimental vapour pressures at different temperatures of four substituted acetophenones. Using the diaphragm manometer static method, the vapour pressures of both (crystalline and liquid) condensed phases of ortho and para acetoxyacetophenones and also of para-methoxyacetophenone were measured in the following temperatures ranges T = (313.0-398.0) K, (315.0-378.3) K and (296.2355.7) K, respectively. This experimental technique was also used to measure the vapour pressnres of the liquid phase of meta-acetoxyacetophenone through the temperature interval T= (305.1-368.5) K. The vapour pressures of the crystalline phase of meta-acetoxyacetophenone were measured using the Knudsen effusion technique over the temperature ranges, T= (297.7-307.3) K. This technique was also used for complementing the range of the vapour pressure measurements of the ortho and para acetoxyacetophenone isomers between T= (298.0-321.3) K and (298.1-309.3) K, respectively. The standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporization, at references temperatures, were derived from the experimental results. Differential scanning calorimetry was used to determine the temperatures and molar enthalpies of fusion and of the observed crystalline transitions. The contribiltions of the acetoxy and acetyl groups to the sublimation properties of the compounds studied were calculated. (c) 2016 Elsevier Ltd.

Abstract This paper proposes an ecological framework "Activities with Parents on the Computer" (APC) to bridge home and school contexts by involving parents and students in digital media based assignments. An exploratory case-study was conducted based on ten parent-child dyads that engaged in an APC at home. Attitudes were assessed through a self-evaluation questionnaire. Four parent-child dyads, that showed different patterns of attitudes, were studied in depth through semi-structured interviews. The findings revealed that parents and children have mixed attitudes towards APC. The performance in the activity varied according to the kind of parental involvement in homework and individuals' relationship with digital media. Relevant insights helped to reframe the model in order to evaluate the relations with other living elements (e.g., friends) brought by technology into the ecological microsystems (e.g., home, school). Future research should focus on the development of more accurate instruments of evaluation, the role of teachers and other community members.

Abstract This work reports experimental sublimation and vaporization vapor pressures at different temperatures of the three isomers of hydroxybenzaldehyde. A static method based on capacitance diaphragm manometers was used to measure the vapor pressures of both (crystalline and liquid) condensed phases of ortho, meta, and para hydroxybenzaldehydes, through the temperature ranges T = (264.6 to 341.7) K, T = (324.9 to 419.4) K, and T = (334.9 to 429.4) K, respectively. The Knudsen mass loss effusion technique was also used to determine the vapor pressures of crystalline meta and para isomers in the temperature intervals T = (309.1 to 331.2) K and T = (319.1 to 341.2) K, respectively. The obtained results enabled the determination of the standard molar enthalpies and entropies of sublimation and of vaporization, at chosen reference temperatures, as well as the (p,T) values of the triple point of the compounds studied. The temperatures and enthalpies of fusion were determined from differential scanning calorimetry. The contributions of the formyl group to the sublimation properties of benzaldehydes were determined, and the standard Gibbs energies of formation in condensed and gaseous phases were calculated.

Abstract In the present work, a combined experimental and computational thermochemical study of nitroimidazole isomers was carried out. The standard (p = 0.1 MPa) molar enthalpy of combustion, in the crystalline phase, for 4-nitroimidazole was determined, at the temperature of 298.15 K, using a static bomb combustion calorimeter. Calvet microcalorimetry experiments were performed to measure its standard molar enthalpy of sublimation. The standard molar enthalpy of formation of 4-nitroimidazole, in the gaseous phase, at T = 298.15 K, (116.9 +/- 2.9) kJ.mol(-1), has been derived from the corresponding standard molar enthalpy of formation in the crystalline phase and the standard molar enthalpy of sublimation. Computational studies for 4-nitroimidazole were performed to complement the experimental work. These were also extended to the 2- and 5-nitroimidazole isomers. The gas-phase enthalpies of formation were estimated from high level ab initio molecular orbital calculations, at the G3 level. Also investigated were the tautomeric equilibrium of 4(5)-nitroimidazole in the gaseous phase and it was concluded that the two tautomers are equally stable. (C) 2016 Elsevier Ltd.

Abstract Thermodynamic properties of 9,9-dimethylxanthene and 2,7-di-tert-butyl-9,9-dimethylxanthene for the condensed and gas states were derived from experimental and computational studies. Static-bomb combustion calorimetry, vacuum drop microcalorimetry and the Knudsen effusion techniques were used. Computational calculations of the enthalpies of hypothetical reactions in the gaseous phase, using the G3(MP2)//B3LYP composite method, were performed for the two xanthene derivatives. Natural bond orbital (NBO) calculations were also performed to ascertain the structure and reactivity of these compounds. The energetic effects caused by replacing hydrogen atoms in the xanthene moiety by methyl and tertbutyl groups yielding 9,9-dimethylxanthene and 2,7-di-tert-butyl-9,9-dimethylxanthene species were determined from direct comparison of their standard (p degrees = 0.1 MPa) molar enthalpies of formation in the gaseous phase, at T=298.15 K. (C) 2016 Elsevier Ltd.