Publications

Abstract Debundling and dispersing single-walled carbon nanotubes (SWNTs) is essential for applications, but the process is not well understood. In this work, aqueous SWNT dispersions were produced by sonicating pristine SWNT powder in the presence of an amphiphilic triblock copolymer (Pluronic F127) as dispersant. Upon centrifugation, one obtains a supernatant with suspended individual tubes and thin bundles and a precipitate with large bundles (and impurities). In the supernatant, that constitutes the final dispersion, we determined the dispersed SWNT concentration by thermogravi-metric analysis (TGA) and UV-vis spectroscopy, and the dispersant concentration by NMR The fraction of dispersant adsorbed at the SWNT surface was obtained by H-1 diffusion NMR Sigmoidal dispersion curves recording the concentration of dispersed SWNTs as a function of supernatant dispersant concentration were obtained at different SWNT loadings and sonication times. As SWNT bundles are debundled into smaller and smaller ones, the essential role of the dispersant is to sufficiently quickly cover the freshly exposed surfaces created by shear forces induced during sonication. Primarily kinetic reasons are behind the need for dispersant concentrations required to reach a substantial SWNT concentration. Centrifugation sets the size threshold below which SWNT particles are retained in the dispersion and consequently determines the SWNT concentration as a function of sonication time.

Abstract The standard (p(o) = 0.1 MPa) molar enthalpy of formation of crystalline uridine, (C9H12N2O6), was determined from its specific energy of combustion, measured by static bomb combustion calorimetry, in oxygen, at T = 298.15 K, as - (1159.8 +/- 1.8) kJ mol(-1). Gas-phase standard molar enthalpy of formation of uridine was determined as - (992.8 +/- 3.2) kJ mol(-1) from quantum-chemical calculations using the G3(MP2) method. The enthalpy of sublimation of uridine at T = 298.15 K, determined as the difference between standard molar enthalpies of formation of uridine in crystalline and gaseous states, was found to be (167.0 +/- 3.7) kJ mol(-1). (C) 2018 Elsevier Ltd.

Abstract When using amphiphilic polymers to exfoliate and disperse carbon nanotubes in water, the balance between the hydrophobic and hydrophilic moieties is critical and nontrivial. Here, we investigate the mode of surface attachment of a triblock copolymer, Pluronics F127, composed of a central hydrophobic polypropylene oxide block flanked by hydrophilic polyethylene oxide blocks, onto single-walled carbon nanotubes (SWNTs). Crucially, we analyze the composition in dispersant of both the as-obtained dispersion (the supernatant) and the precipitate-containing undispersed materials. For this, we combine the carefully obtained data from H-1 NMR peak intensities and self-diffusion and thermogravimetric analysis. The molecular motions behind the observed NMR features are clarified. We find that the hydrophobic blocks attach to the dispersed SWNT surface and remain significantly immobilized leading to H-1 NMR signal loss. On the other hand, the hydrophilic blocks remain highly mobile and thus readily detectable by NMR. The dispersant is shown to possess significant block polydispersity that has a large effect on dispersibility. Polymers with large hydrophobic blocks adsorb on the surface of the carbonaceous particles that precipitate, indicating that although a larger hydrophobic block is good for enhancing adsorption, it may be less effective in dispersing the tubes. A model is also proposed that consistently explains our observations in SWNT dispersions and some contradicting findings obtained previously in carbon nanohorn dispersions. Overall, our findings help elucidating the molecular picture of the dispersion process for SWNTs and are of interest when looking for more effective (i.e., well-balanced) polymeric dispersants.

Abstract Approximately half the students enrolled in the many arts and design undergraduate programmes offered by Portuguese public higher education institutions will learn or have an opportunity to learn about computer programming while taking their degree. A preliminary study to assess those students' attitudes and opinions towards the subject of programming was conducted using an online survey based on Unified Theory of Acceptance and Use of Technology (UTAUT). An opportunity sample of 187 students participated, and 41.2% reported proficiency in some form of computer programming, 35.8% reported to be currently learning, and only 23% reported no knowledge of the subject. Expectations of utility, effortlessness and peer approval were found to positively correlate with students' intention to program or, in the case of students without such knowledge, an intention to learn computer programming. Students currently learning to code reported greater anxiety about the subject overall, and those reporting greater anxiety had the least intention to program in the future. Female students were also more likely to ascribe greater anxiety to the perspective of programming computers, as did younger students in general. Mitigating anxiety thus presents a challenge to educators engaged with computer programming, alongside adapting syllabi and pedagogies as to reduce the gender imbalance in programming acceptance and use.

Abstract A review of arts and design undergraduate programmes offered by Portuguese public higher education institutions found out that 50 out of the 105 programmes include at least one unit concerning computer programming in their curricula. A preliminary study partially based on the Unified Theory of Acceptance and Use of Technology (UTAUT), conducted through an online survey, sought to find out how lecturers in those programmes regard the subject of computer programming. A sample of 68 educators participated, split between 43 that reported no knowledge of computer programming and 25 that reported programming proficiency, 14 of which were engaged teaching the subject. A noticeable gender discrepancy was found concerning proficiency, raising the question of whether there's a relation to the anxieties of female students regarding programming found in a related study. Commenting on the relevance of the subject, some educators stressed that coding is both a fundamental problem-solving tool and a means to teach logical thinking, while others highlighted the creative potential of programming. Given the push to demystify computer programming, institutions can be encouraged to reduce the gender imbalance in the programming competency of educators. More research concerning educators' attitudes towards programming is welcome, both through practice characterization case-studies and through a deeper understanding of technology acceptance models applied in higher arts and design education.

Abstract An energetic study of 5-fluoro-2-methylbenzoxazole (FMBO) and of 5-fluoro-2-methylbenzothiazole (FMBT), in condensed and gaseous states, has been performed using calorimetric techniques and computational calculations. The standard (p degrees = 0.1 MPa) molar enthalpies of formation of FMBO and FMBT, in the liquid phase, at T = 298.15 K, were derived from the corresponding standard molar energies of combustion, measured by rotating-bomb combustion calorimetry. At T = 298.15 K, the standard (p degrees = 0.1 MPa) molar enthalpy of vaporization, for each compound, was determined, by a direct method, using the vacuum drop microcalorimetric technique. For each compound, from this last value and from the enthalpy of formation of the liquid compounds, the corresponding standard (p degrees = 0.1 MPa) enthalpy of formation in the gaseous phase has been calculated. Additionally, the gas-phase standard molar enthalpies of formation of these two compounds were estimated computationally at the G3(MP2)//B3LYP level of theory, as well as their gas-phase basicities and proton affinities. (C) 2018 Elsevier Ltd.

Abstract The energetic study of 2-methylnaphtho[1,2-d] oxazole (MN12O), 2-methylnaphtho-[2,3-d] oxazole (MN23O) and 2-methylnaphtho[1,2-d] thiazole (MN12T) has been performed experimental and computationally. The enthalpies of combustion and sublimation/vaporization of these compounds were determined, respectively, from static or rotating bomb combustion calorimetry and high temperature Calvet microcalorimetry and/or the Knudsen-effusion studies. These experimental data allow derivation of the corresponding gas-phase standard molar enthalpies of formation of the three compounds. Additionally, we have obtained the gas-phase standard molar enthalpies of formation of these three compounds, as well of the 2-methylnaphtho[2,3-d] thiazole (MN23T), through high level ab initio calculations, at the G3(MP2)//B3LYP and DLPNO-CCSD(T)/cc-pVTZ levels of theory. The computational study of the molecular structures of the compounds has been carried out. Furthermore, a relationship between the energetic and structural characteristics of these molecules was also evaluated. (C) 2018 Elsevier Ltd.

Abstract Steady-state and time-resolved fluorescence techniques as well as quantum-mechanical calculations were used to study the photophysics and photochemistry of a newly synthesized photoacid. the phenol cyanine picolinium salt. We found that the nonradiative rate constant k(nr) of the excited protonated form of the photoacid is larger than that of the excited-state proton transfer (ESPT) to the solvent, k(ESPT). We estimate that the quantum efficiency of the ESPT process is about 0.16. The nonradiative process is explained by a partial trans-cis isomerization reaction, which leads to the formation of a "dark" excited state that can cross to the ground state by nonadiabatic coupling. Moreover, the ESPT process is coupled to the photo-isomerization reaction, as this latter reaction enhances the photoacidity of the studied compound, as a result of photoinduced charge transfer. To prevent trans-cis isomerization of the cyanine bridge, we conducted experiments of PCyP adsorbed on cellulose in the presence of water. We found that the steadystate fluorescence intensity increased by about a factor of 50 and the lifetime of the ROH band increased by the same factor. The fluorescence intensity of the RO(-)band with respect to that of the ROH band was the same as in aqueous solution. This explains why inhibiting the photo-isomerization reaction by adsorbing the PCyP on cellulose does not lead to a higher ESPT rate.

Abstract The present work addresses computational research focused on the energetic and structural properties of four isomers monohydroxyxanthone, using the G3(MP2)//B3LYP method, in order to evaluate the influence of the hydroxyl (-OH moiety) functional group on the xanthone molecule. The combination of these computational results with previous experimental data of these compounds enabled the determination of their enthalpies, entropies and Gibbs energies of formation, in the gaseous phase, and consequently to infer about the relative thermodynamic stability of the four isomers. Other issues were also addressed for the hydroxyxanthone isomers, namely the conformational and the tautomeric equilibrium analysis of the optimized molecular structures, the frontier orbitals, and the electrostatic potential energy maps. Complementarily, an energetic study of the intramolecular OH center dot center dot center dot O hydrogen bond for 1-hydroxanthone was also performed.

Abstract This work describes the synthesis, structural and optical properties of Tm3+/Yb-3 doped and Ca2+ co-doped YF3 upconversion phosphor material. The effect of Ca2+ ions co-dopant concentration is varied at 0, 10, 20 and 30 mol% to observe it's effect on YF3:Tm3+/Yb3+ through different characterizations like XRD, XPS, FE-SEM, FTIR, UV-vis and upconversion measurements. Dominant upconversion emission bands are found at 450, 476, 645 and 696 nm emission wavelengths corresponding to the D-1(2)-> F-3(4), (1)G(4)-> H-3(6) (1)G(4)-> F-3(4) and F-3(3)-> H-3(6) transitions within Tm3+ activator center on 976nm excitation. Finally, prepared samples are utilized in temperature sensing application demonstrations with Ca2+ ions co-dopants concentration variations.